ObjectiveTo review the history of chondrocyte transplantation, new approaches to treatment of human chondral and osteochondral defects, animal experiments, the choice of chondrocytes for transplantation, immunological features of human and animal chondrocytes and factors which could influence results of chondrocyte transplantation.DesignAs the material for review served numerous papers collected during our many years' chondrocyte studies supplemented by PubMed search.ResultsAutologous chondrocytes, expanded in culture, were successfully used to repair damaged human articular cartilage. Numerous modifications of the original procedure benefited from a better understanding of factors influencing chondrocyte differentiation. Immunological studies suggested that survival of allogeneic transplants of bioengineered human neocartilage may depend on both passive and active mechanisms of immune evasion. Human chondrocytes with deleted expression of MHC class I molecules produced cartilage which, after transplantation into monkey articular cartilage was attacked by NK cells.ConclusionsImmune response against human chondrocytes requires further investigation. It is already established that allogeneic chondrocytes are safe for treating chondral defects but not for healing osteochondral defects. Full reconstruction of cartilage defects by restoring anatomically identical hyaline cartilage seems not feasible.

BACKGROUND:Bone morphogenetic proteins (BMPs) are used in clinical practice for the stimulation of bone formation, but can often lead to serious complications. Recent studies have demonstrated that BMPs involved in the early stages of bone formation are species-specific. In cattle the most common forms encountered are BMP7, growth differentiation factor 5 (GDF5), and NEL-like protein 1 (NELL1), while in rats the most common are BMP2, BMP5 and BMP6. The aim of this study was to compare the action of species-specific BMPs on osteoprogenitor cells. Thus, rat osteoprogenitor cells were exposed to one BMP in a high dose, and three of them at one third of the high dose. MATERIALS AND METHODS:Isolated rat osteoprogenitor cells were treated in culture with different concentrations of BMP2, BMP5 and BMP6 or with lower concentrations of combinations of these cytokines. The activity of alkaline phosphatase, calcium deposition and mRNA level for transcription factor SP7 (osterix) and tissue non-specific alkaline phosphatase (TNAP) served as indicators of BMPs effect. RESULTS:BMPs stimulated all studied parameters compared to control cultures, but no statistically significant differences were observed between the action of a large dose of one cytokine and a combination of cytokines given at lower concentrations. CONCLUSIONS:Three BMPs used in a low dose exert a similar effect to one used in a high dose. Since the BMPs stimulate different receptors, and activate different signalling pathways, using a mixture of properly chosen BMPs at a low concentration may give better results than a single one at a high concentration, and may avoid untoward effects.

Endometriosis is a common chronic gynaecological disorder related to the presence of ectopic foci of endometrial-like tissue, mostly in the pelvic cavity. Pathogenesis of this disease may be associated with epithelial-to-mesenchymal transition (EMT), a phenomenon defined by morphological and functional changes from epithelial to mesenchymal cell phenotype. The role of EMT in the development of endometriotic lesions remains poorly understood. There is also little known about the role of EMT in the eutopic endometrium in course of the menstrual cycle. Therefore, the present study was aimed at investigating the expression of major EMT-related genes of TGF-β, ZEB, SNAIL, CDH, and miR200 families in eutopic endometrium of women with and without endometriosis in the proliferative and secretory phase of the menstrual cycle. The study included 46 women with endometriosis and 30 control women without symptoms of the disease. Eutopic endometrial tissue samples were collected during the mid-proliferative and mid-secretory phases. Tissue localization of the tested factors was detected by immunohistochemical staining. Expression of specific RNAs was evaluated by quantitative RT-PCR. Differences between groups were determined using the Student’s t-test, Wilcoxon matched-pairs signed rank test or Mann–Whitney U-test. All investigated factors were expressed in the eutopic endometrium, both at the protein and mRNA levels. Comparison of mRNA expression during different cycle phases has revealed a significant upregulation of SNAI2 mRNA in the secretory phase in both the endometriosis and control groups. The secretory phase was also associated with a decreased expression of CDH2 mRNA in the control group. However, a similar difference was not revealed in the endometriosis patients. There were no differences in mRNA levels of the other tested EMT-related factors between the endometriosis and control groups, regardless of the cycle phase. The present study shows that SNAI2 expression is upregulated during the secretory phase of the menstrual cycle, thus suggesting its role in the physiology of the cyclic endometrial changes. However, our data argue for a limited role of EMT in eutopic endometrium in the pathogenesis of endometriosis. These findings put new light on the physiology of the endometrium and the role of EMT in the pathogenesis of endometriosis.

Ceramic materials produced by various methods from calcium phosphates have long been used in orthopaedic and dental surgery. Until recently, it was generally believed that at least some of them faithfully reproduce bone minerals. Newer studies, however, have shown that hydroxyapatite in bone is closely associated with citrate molecules. This raises the yet unanswered question whether the materials used in clinical practice are optimal in relation to the tasks which they are supposed to fulfil. The description of the function of citrate in bone mineralization requires appropriate background information, which is presented in this review.

Biomimetic production of coatings on various types of scaffolds is based mainly on simulated body fluid pre-cipitation (SBF) of apatites, or, if the HCO3  is present, carbonated apatites. Recently, we proposed formation of calcium phosphates (CaP) precipitates by alkaline phosphatase (ALP) hydrolysing glycerophosphate in presence of calcium ions as an alternative to SBF. Since apatites synthesized in bone by the ALP activity contain carbonate anions, it was tempting to investigate whether the phosphatase method could be advanced into osteomimetic one. Therefore, taking example from the SBF studies, phosphatase incubation medium was enriched with car-bonate ions at 4.2 and 27 mM concentration. X-ray diffraction of the precipitates disclosed peaks typical for hydroxyapatite (HAP). FTIR analysis showed that at both concentration of carbonate ions, apatites underwent both B and A substitution, more extensive at higher concentration. Thus, osteomimetic approach produced carbonated hydroxyapatites of the type encountered in bone tissue even at HCO3  concentration as low as 4.2 mM. Composite plates made of poly(& epsilon;-caprolactone) and mixture of & beta;-tricalcium phosphate and hydroxyapatite at mass ratio of 1:0.5:0.5, respectively, were covered by CaP coatings, i.e., CaP-0, CaP-4.2, CaP-27, by incubation in phosphatase medium containing 0, 4.2 or 27 mM of NaHCO3, respectively. Pristine or coated PCL50 plates were used to study release of calcium and adsorption/desorption of proteins, or seeded with human bone marrow mesenchymal stem cells (hMSC) for study of cell adhesion, spreading and osteogenic differentiation. Introduction of carbonate into the CaP coatings significantly increased release of Ca2+ in a carbonate concentration-dependent manner; the release was up to 4 times higher, when compared to CaP-0 coating, and reached 0.41 & PLUSMN; 0.01 mM for CaP-27 after first 24 h. Coating CaP-4.2 yielded significantly higher adsorption of bovine serum albumin and cytochrome C than CaP-0. All of the CaP coatings improved significantly hMSC adhesion, however, only CaP-4.2 provided 2 times higher cell number than PCL50 after 2 weeks of culture. Interestingly, ALP activity calculated per cell number was the highest on pristine plates, presumably because hMSC differentiate preferentially into osteoblasts at lower seeding densities. It appears, therefore, that the osteomimetic approach may be useful for production of carbonated hydroxyapatite coatings, but requires further studies and replacing intestinal phos-phatase used in this work with one originating from bone.

The discovery of bone morphogenetic proteins (BMPs) inspired hope for the successful treatment of bone disorders, but side effects worsening the clinical effects were eventually observed. BMPs exert a synergistic effect, stimulating osteogenesis; however, predicting the best composition of growth factors for use in humans is difficult. Chondrocytes present within the growth plate produce growth factors stored in calcified cartilage adhering to metaphysis. These factors stimulate initial bone formation in metaphysis. We have previously determined the growth factors present in bovine calcified cartilage and produced by rat epiphyseal chondrocytes. The results suggest that growth factors stimulating physiological ossification are species dependent. The collection of human calcified cartilage for growth factors determination does not appear feasible, but chondrocytes for mRNA determination could be obtained. Their collection from young recipients, in view of the Academy of Medical Royal Colleges Recommendation, would be ethical. The authors of this review do not have facilities to conduct such a study and can only appeal to competent institutions to undertake the task. The results could help to formulate a better recipe for the stimulation of bone formation and improve clinical results.

Endometriosis is a common gynecological disorder defined as the presence of endometrial-like tissue (glands and stroma) outside the uterus. The etiopathogenesis of endometriosis is still poorly recognized. It is speculated that stage-specific embryonic antigen 1 (SSEA-1)-positive stem-like glandular epithelial cells may contribute to the development of the disease. The synthesis of SSEA-1 is mediated by fucosyltransferase 4 encoded by the FUT4 gene. Therefore, this study aimed to evaluate the specific expression of FUT4 mRNA in biopsies of the endometrium from women with and without endometriosis. FUT4 mRNA levels were examined in 49 women with laparoscopically confirmed endometriosis and 28 controls by means of quantitative reverse-transcription polymerase chain reaction (qRT-PCR). The expression of FUT4 mRNA was significantly increased in the endometrium of patients with endometriosis when compared to the controls (p < 0.0001). Expression of FUT4 mRNA in the endometrium was correlated with the severity of endometriosis (rs = 0.5579, p < 0.0001); however, there were no differences in endometrial FUT4 mRNA expression when comparing endometriotic lesions from various locations. The discriminatory ability of FUT4 mRNA expression was evaluated by receiver-operating characteristics (ROC), which showed high statistical significance (AUC = 0.90, p < 0.0001), thus indicating that an increased level of endometrial FUT4 mRNA may serve as a specific marker for endometriosis.

To the Editor: We read with interest the review published in the Journal of Bone Mineral Research (JBMR) titled: “The Diverse Origin of Bone-Forming Osteoblasts” by Mizoguchi and Ono.(1) The authors describe findings indicating that osteoblasts involved in bone formation under various physiological, pathological, and therapeutic conditions can be obtained from numerous sources. Further, the authors write: “However, whether osteoblasts derived from different cellular sources have distinct functions remains to be investigated.” As a matter of fact, such studies have already been done—more than 30 years ago. Osteoblasts, preosteoblasts, and other osteoprogenitor cells were isolated with collagenase from calvariae of fetal rats and used to study bone morphogenesis in syngeneic and allogeneic intramuscular transplants. Transplanted cells formed islands of woven bone, which increased in size and fused. At the surface of the woven bone lamellar bone developed. Osteoclasts were scarce and the woven bone remained unresorbed. Bone marrow was absent. Bone formed in an allogeneic system was surrounded by infiltrations and rejected.(2) Another, earlier study demonstrated that transplanted chondrocytes isolated from endochondral cartilage produce structure resembling epiphyseal growth plate which serves as the base for endochondral bone formation.(3) In situ structural differences between calvarial and endochondral bones are well known; it seemed, however, interesting to see to what extent they are preserved in transplants. It has been found that the area of bone marrow cavities, in relation to the bone tissue, was about 20-fold larger in endochondral bone than in the bone formed by transplanted calvarial cells. The area occupied by bone marrow in intact parietal bones was only twofold greater than in bone formed in transplants. Thus, structural differences between calvarial and endochondral bones observed in vivo were also present in transplants.(4) In further studies, calvarial and scapular osteoblasts were isolated from young rats. In intact scapulas of 28-day-old rats the percentage area occupied by bone tissue in relation to bone marrow was six times larger than in parietal bones of comparable age. Isolated scapular osteoblasts usually produced an ossicle with similar general structure and ratio of bone tissue/bone marrow area as in intact scapulas. In transplants of calvarial osteoblasts numerous islands of bone tissue with the small amount of bone marrow appeared. These results suggested that osteoblasts from endochondral scapular bone may have different properties than those from intramembranous calvarial bones.(5) It is, however, necessary to stress that besides osteoblasts our transplants presumably contained also less differentiated osteoprogenitor cells and thus different outcomes could be influenced by the relative composition of the transplanted populations. To compare the properties of osteoblasts from endochondral bones, rat scapulas and vertebral, isolated osteoblasts were transplanted intramuscularly in “sandwiches” made of devitalized calvarial vaults. The structure of transplants produced by both types of bone cells appeared similar. Woven bone predominated in 4-week-old transplants. The area occupied on the cross-sections of transplants by bone tissue was considerably larger than that of the bone marrow cavities. Transplants of 8-week duration contained mainly cancellous bone and the area taken by medullary space was larger than that of bone tissue. This findings suggested that osteoblasts from various endochondral bones have similar properties.(6) Thus, our studies demonstrated that intramuscularly transplanted isolated osteoblasts or preosteoblasts produce bone along the same lines as in normal development. Woven bone is formed first, lamellar bone appears at the later stage, independently, whether osteoblasts were isolated from woven or lamellar bone surface. Cells isolated from calvarial bones produce bone with small medullary spaces, whereas cells from endochondral bone (in practice from the surface of trabeculae of spongy bone) produce bone with large medullary spaces. Therefore, both of these cell types do not appear suitable as the source of osteoblasts for reconstruction of bone with good mechanical properties. The idea that mesenchymal stem cells originating from bone marrow are good candidates for osteoblasts in reconstructive bone surgery requires verification. Will they form bone with good mechanical properties after transplantation? It would be prudent to settle the point by transplanting them into athymic animals. The best source of cells for formation of cancellous bone typical for long bones would probably be periosteal stem cells,(7) unfortunately they were not recognized at the time when we actively worked in the field. The authors state that they do not have any conflicts of interests. Stanisław Moskalewski: Conceptualization; investigation; writing – original draft. Jacek Malejczyk: Investigation; writing – original draft. Anna Osiecka-Iwan: Data curation; investigation; writing – review and editing. Anna Hyc: Data curation; investigation; writing – review and editing.

INTRODUCTION:In endochondral ossification septoclasts and osteoclasts (also called chondroclasts) release growth factors deposited in non-calcified and calcified zones of the growth plate. They stimulate, within the metaphysis, initial stages of the bone formation. We have recently reported quantitation of several growth factors in calcified cartilage from calf costochondral junction. Data from the analogous human cartilage could possibly help to choose efficient combinations of growth factors for clinical applications, but the amount of the calcified cartilage needed for analysis of numerous growth factors would be difficult to collect. The estimation of growth factors expression in endochondral chondrocytes may, indirectly, indicate which of them play a leading role in the stimulation of osteoprogenitor cells in metaphysis. To test this hypothesis, we used rat chondrocytes to evaluate mRNA levels of several growth factors.MATERIALS AND METHODS:Chondrocytes were isolated from proliferative and hypertrophic zones of the epiphyseal cartilage forming costochondral junctions of inbred Lewis rats. The total RNA was isolated from chondrocytes and the level of mRNA for bone morphogenetic proteins 1-7 (BMP-1-7), vascular endothelial growth factor A (VEGF-A), basic fibroblast growth factor (bFGF), growth/differentiation factor 5 (GDF-5), NEL-like protein 1 (NELL-1), transforming growth factor beta 1 (TGF-b1), mesencephalic astrocyte-derived neurotrophic factor (MANF), connective tissue growth factor (CTGF), osteoclast-stimulating factor 1 (OSTF-1) and insulin-like growth factor 1 (IGF-1) was evaluated using real-time PCR method.RESULTS:All studied factors were expressed. The highest level of mRNA was detected for CTGF, MANF, VEGF-A and TGF-b1. Expression was also quite high for BMP-1, BMP-2, BMP-5, BMP-6, BMP-7, IGF-1, GDF-5 and OSTF-1. Very low level of mRNA was detected for BMP-3, BMP-4 and NELL-1.CONCLUSIONS:Chondrocytes from the proliferative and hypertrophic zones of the growth plate produce factors involved in the cartilage metabolism and bone formation. The determination of these growth factors in humans could help to choose their optimal composition necessary for stimulation of bone formation in clinical practice. In rat the best stimulation of bone formation would presumably be achieved with a mixture of BMP-2, BMP-5, BMP-6 and BMP-7.

Objective Initial stages of cartilage matrix calcification depend on the activity of matrix vesicles. The purpose of the study was to describe how calcified matrix vesicles join into larger structures, to present their up-to-date undescribed 3-dimensional image, and to observe how calcified matrix relates to chondrocyte lacunae. Design Calcified cartilage was obtained from the zone of provisional calcification of calf costochondral junctions, then enzymatically isolated and studied by microtomography, scanning electron microscopy, atomic force microscopy and X-ray diffraction, and Fourier transform infrared spectroscopy. Results Hyaluronidase digestion released packets of granules surrounded by the cartilage matrix. Further digestion, with collagenase and trypsin, removed matrix and exposed granules with dimensions within 50 to 150 nm range, which we consider as equivalent of calcified matrix vesicles. Granules joined into larger groups with dimensions of 0.5 to 2 μm, which we call globular units. Certain matrix vesicles appeared well connected but contained globular units that had spaces filled with electron lucent material, presumably matrix or chondrocyte remnants. Globular units were organized into massive structures taking the shape of oval plates. Comparison of these plates with lacunae containing isogenous groups of chondrocytes from proliferative zone of costochondral junction suggests that the cells from a single lacuna were responsible for the formation of one plate. The plates were connected with each other and extended over provisional calcification zone. Conclusions The outcome showed how particular calcified matrix vesicles associate into globular units, which organize into massive structures assuming the shape of oval plates and eventually cover large areas of cartilage matrix.

Endochondral bone formation is orchestrated by growth factors produced by chondrocytes and deposited in the cartilage matrix. Whilst some of these factors have been identified, the complete list and their relationship remains unknown. In the present study, the growth factors were isolated from non-calcified and calcified cartilage of costochondral junctions. Cartilage dissected from the ribs of 6-20-week-old calves was purchased from a local butcher within 24 h of the death of the animal. The isolation involved hyaluronidase digestion, guanidinium hydrochloride (GuHCl) extraction, HCl decalcification and GuHCl extraction of the decalcified matrix. Growth factors were purified by heparin chromatography and their quantities were estimated using ELISA. Decalcified cartilage was also used for protein sequence analysis (data are available via ProteomeXchange; ID, PXD021781). Bone morphogenetic protein-7 (BMP-7), growth/differentiation factor-5 (GDF-5) and NEL-like protein-1 (NELL-1), all known growth factors that stimulate bone formation, quantitatively accounted for the majority of the material obtained in all steps of isolation. Thus, cartilage serves as a store for growth factors. During initial bone formation septoclasts release osteoclastogenesis-stimulating factors deposited in non-calcified cartilage. Osteoclasts dissolve calcified cartilage and transport the released factors required for the stimulation of osteoprogenitor cells to deposit osteoid. High concentrations of BMP-7, GDF-5 and NELL-1 at the site of initial bone formation may suggest that their synergistic action favours osteogenesis.

Curcumin (diferuloylmethane) derived from the rhizome of Curcuma longa L. has been used for thousands of years in traditional Chinese medicine and Ayurvedic medicine in Asian countries to treat liver diseases, rheumatoid diseases, diabetes, atherosclerosis, infectious diseases and cancer. It exhibits a wide range of pharmacological properties, which include antioxidant, anti-inflammatory, antimutagenic, antimicrobial and anticancer activity. Herein the mechanisms of curcumin impact on oxidative stress, angiogenesis and inflammatory processes are described indicating that curcumin use may inhibit those pathological conditions and restore body homeostasis. Its effectiveness was also proved for major eye diseases. In this review, the influence of curcumin on eye diseases, such as glaucoma, cataract, age-related macular degeneration, diabetic retinopathy, corneal neovascularization, corneal wound healing, dry eye disease, conjunctivitis, pterygium, anterior uveitis are reported. The analysis of a number of clinical and preclinical investigations indicates that curcumin may be used as a therapeutic agent in the treatment of various eye disorders.

Graves' ophthalmopathy (GO) is an inflammatory autoimmune disorder of the orbital adipose tissue and extraocular muscles, and it is associated with Graves' disease (GD). GO is triggered by binding and activation of orbital fibroblasts by autoantibodies (TSI) direct against thyroid-stimulating hormone receptor (TSHR) and insulin-like growth factor 1 (IGF-1R), which is highly expressed within the orbit. Moreover, interaction of T cells with orbital fibroblasts that involve T-cell receptor (TCR), autoantigen, and major histocompatibility complex class II (MHC II) molecule, as well as CD40:CD154 signalling, activates p38, ERK 1/2, and JNK pathways. These processes induce fibroblast activation, proliferation, and secretion of chemokines and inflammatory cytokines to maintain inflammation within the orbit. Furthermore, increased hyaluronic acid production and fibroblast differentiation into adipocytes and myofibroblasts leads to development of GO. The elevated number of molecular factors such as PDGF, IL1-beta, IL-4, IL-6, IL10, IL-8, IL-16, IL-33, HGF, ICAM-1, osteopontin, CTLA-4, and TGF-beta are discussed in the paper. Some of them are key markers of disease stage. Better understanding of GO pathogenesis leads to development of new therapeutic options.

Fibroblasts produce extracellular matrix (ECM), secrete proteolytic enzymes, their inhibitors, cytokines and growth factors. Their secretory profile varies depending on the organ from which they originate. We previously described the influence of cartilage interstitial fluid (CIF) on the gene expression of ECM proteins, cytokines, metalloproteases and their inhibitors in synovial membrane cells, dermal (DFs) and cruciate ligament fibroblasts (CTLs). In this work we studied the reaction of rat dermal and cruciate ligament fibroblasts to the most abundant CIF cytokines: basic fibroblast growth factor (bFGF), transforming growth factor-beta 1 (TGF-beta 1) and insulin-like growth factor-1 (IGF-1) used in different combinations. The results disclosed several differences in the response of both types of fibroblast to the tested cytokines. For example IGF-1/TGF-beta 1/bFGF triplet stimulated stronger expression of hyaluronan synthases 1 and 2 (Has1 and Has2) in ligament than dermal fibroblasts. Stronger lubricin (Prg4) expression was stimulated by IGF-1/TGF-beta 1 in cruciate ligament than in dermal fibroblasts. Both combinations of cytokines stimulated Tgfb1, tissue inhibitor of metalloproteinases 1 (Timp1), inhibited tumor necrosis factor (Tnf) and metalloproteinase 3 (Mmp3) expression in both types of cells. Because fibroblasts produce different factors in response to the same stimuli, our results provide a better understanding of their role in physiological and pathological processes.

The purpose of this work was to establish, whether rat chondrocyte associated antigen, transmembrane Tmp21 protein belonging to the p24 protein family may immunize rats and thus be included into the panel of immunogens potentially involved in cartilage pathology. For immunization of rats extract from cultured chondrocytes containing surface chondrocyte proteins suspended in incomplete Freund’s adjuvant was used. Control animals were injected with incomplete Freund’s adjuvant without chondrocyte extract. Morphological observations indicated that both in control and experimental animals occurred subperiosteal resorption of bone, suggesting that it arised as the response to adjuvant. In trachea, however, resorption of cartilage and inflammatory changes in the respiratory epithelium and lamina propria were present only in animals exposed to antigen. Unexpectedly, sera from immunized rats strongly reacted with other antigen, which we were able to identify by Western blot and protein sequencing as cartilage oligomeric matrix protein (COMP). COMP is attached to chondrocyte membrane by integrins and its presence in chondrocyte extract is not surprising. Antibody response to COMP raises a question whether the observed changes in tracheal cartilage and epithelium represent anti-COMP reaction or were caused by some other, no specified factors. COMP is used as the marker of osteoarthritis progression, but its role in polychondritis, cartilage pathology involving i.a. tracheal cartilage resorption remains unknown. Thus, our observations may serve as the starting point for future studies in this direction.

Ghrelin has been found to be expressed in the human endometrium. Emerging evidence links ghrelin and its receptor with the reproductive system. Certain associations between ghrelin and angiogenesis have also been established. The aim of this small case-control study was to quantify and compare the expression of mRNA encoding ghrelin, ghrelin receptor (GHS-R), vascular endothelial growth factor A (VEGF A) and its receptors (VEGFR1-3) in the endometrium of women with recurrent miscarriage compared to parous controls. Correlations between the expression of particular genes were also investigated. Endometrial samples were obtained during the secretory phase of the menstrual cycle from 15 women with a history of recurrent miscarriage (first trimester pregnancy loss without a known cause) and 10 healthy parous controls. Ghrelin, GHS-R, VEGF A and VEGFR1-3 mRNA expression was analyzed by quantitative RT-PCR. The expression of mRNA for ghrelin and VEGF A was significantly higher in the study group than the control group. In the control group, the expression of ghrelin mRNA was positively correlated with the expression of VEGF A and VEGFR1 mRNA. In the study group, no such associations were observed. These results show that the expression of mRNA for ghrelin and VEGF A may be increased in the endometrium of women with recurrent miscarriage thus suggesting that ghrelin may play a role in the pathogenesis of recurrent miscarriage.

The paper presents a novel approach to the production of calcium phosphate coatings of scaffolds. Mineral deposits were formed during incubation of polycaprolactone (PCL) scaffolds with bovine intestinal alkaline phosphatase in sodium glycerophosphate and calcium chloride medium. To modify hydrophobic surface of scaffolds and intensify attachment of coating, scaffolds were incubated at 50 °C (thermal activation, TA) or at 37 °C after short exposition to lipase (lipase activation, LA). Micro-computed tomography observations demonstrated that both methods resulted in deposition of mineral on the surface of external and internal walls of the scaffolds. Precipitate formed after thermal and lipase activation contained particles with average size of 200-400 nm, and the shape of donuts. In thermal activated PCL coatings X-ray diffraction disclosed peaks typical for hydroxyapatite (HAp), while after lipase activation these peaks could be precisely defined only if left for 6 days in the incubation medium. The Fourier-transform infrared spectroscopy suggested crystalline structure of HAp both after thermal and lipase activation. The adherence of bone marrow mesenchymal stem cells was initially higher on coated than pristine PCL, but during 7 days of culture the cell number increased and was similar on all tested samples. Alkaline phosphatase activity, considered as a sign of osteogenic differentiation, measured on PCL samples after 7 days was 2-3 times lower on pristine PCL than on the coated samples, but after 2 weeks increased significantly and reached similar value as on the calcium phosphate substrates.

In physiological conditions chondrocytes are protected from contact with immunocompetent cells by the extracellular matrix, and transplanted fragments of allogeneic cartilage are not rejected. Cartilage produced by allogeneic chondrocytes, however, evokes the immune response of the recipient and is gradually destroyed. Immunisation by allogeneic chondrocytes is induced by the contact of their surface molecules with cells of the immune system. Chondrocytes constitutively express class I and, in some species, class II major histocompatibility complex (MHC) molecules. Expression of MHC class II molecules is induced in vitro by pro-inflammatory cytokines and in vivo in the course of the rejection of transplanted allogeneic cartilage. Low level of MHC class II molecules is found on the surface of human articular chondrocytes in patients with rheumatoid arthritis and osteoarthritis. Cartilage produced by transplanted allogeneic chondrocytes is destroyed by monocytes/macrophages and cytotoxic T and natural killer (NK) cells. NK cells show spontaneous cytotoxic reactivity against isolated chondrocytes and participate in the rejection of transplanted isolated chondrocytes. Chondrocytes express molecules that can serve as potential antigens in inflammatory joint diseases. Chondrocytes express cartilage-specific membrane antigen (CH65), human cartilage glycoprotein-39 (HC gp-39), hyaluronan binding adhesion molecule CD44, thymocyte antigen-1 (Thy-1) - CD90, signal transducer - CD24, lymphocyte function-associated antigen-3 (LFA-3) - CD58, and type I transmembrane protein Tmp21. On the other hand, although chondrocytes express major histocompatibility complex (MHC) class I and class II molecules, they can also exert immunosuppressive and immunomodulatory effects on immunocompetent cells. Isolated chondrocytes do not trigger an efficient allogeneic immune response in vitro and suppress, in a contact-dependent manner, proliferation of activated T cells. This suppression is associated with the expression by chondrocytes of multiple negative regulators of immune response. Chondrocytes express programmed death-ligand (PD-L), chondromodulin-I and indoleamine 2,3-dioxygenase (IDO), molecules that promote self-tolerance and suppress the immune system.