OBJECTIVE To evaluate the role of the nuclear factor-kappaB (NF-kappaB) in the response of bovine monocytes to exposure to Mycobacterium avium subsp paratuberculosis (MAP). SAMPLE POPULATION Monocytes from healthy adult Holstein cows that were known to be negative for MAP infection. PROCEDURES Monocytes were incubated with MAP organisms with or without a specific inhibitor of the NF-kappaB pathway (pyrrolidine dithiocarbamate), and activation of the NF-kappaB pathway was detected by use of an electrophorectic mobility shift assay. The capacities of monocytes to express tumor necrosis factor (TNF)-alpha, interleukin (IL)-10, and IL-12; to acidify phagosomes; to phagocytize and kill MAP organisms; and to undergo apoptosis were evaluated. RESULTS Addition of MAP organisms to monocytes activated the NF-kappaB pathway as indicated by increased NF-kappaB-DNA binding. Addition of pyrrolidine dithiocarbamate prevented nuclear translocation of NF-kappaB, decreased expression of TNF-alpha and IL-10, and increased IL-12 expression. Treatment of MAP-exposed monocytes with pyrrolidine dithiocarbamate increased the rate of apoptosis but failed to alter phagosome acidification, organism uptake, or organism killing by those cells. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that NF-kappaB rapidly translocated to the nucleus after exposure of bovine monocytes to MAP organisms. These data suggest that NF-kappaB is involved in initiation of inflammatory cytokine transcription and inhibition of apoptosis but that it is not directly involved in phagosome acidification or organism killing.

Pathogenic mycobacterial organisms have the capacity to inhibit macrophage activation and phagosome maturation. Although the mechanism is complex, several studies have incriminated signaling through TLR2 receptors with subsequent activation of the MAPK pathway p38 (MAPKp38) and overproduction of IL-10 in the survival of pathogenic mycobacterial organisms. In the present study, we compared the response of bovine monocytes with infection by Mycobacterium avium subspecies paratuberculosis (MAP), the cause of paratuberculosis in ruminants, with the closely related organism M. avium subspecies avium (Maa), which usually does not cause disease in ruminants. Both MAP and Maa induced phosphorylation of MAPKp38 by bovine monocytes; however, addition of a blocking anti-TLR2 antibody partially prevented MAPKp38 phosphorylation of MAP-infected monocytes but not Maa-infected monocytes. Addition of anti-TLR2 antibody enhanced phagosome acidification and phagosome-lysosome fusion in MAP-containing phagosomes and enabled monocytes to kill MAP organisms. These changes were not observed in Maa-infected monocytes. The effect on phagosome maturation appears to occur independently from the previously described inhibitory effects of IL-10 on phagosome acidification and organism killing, as IL-10 production was not affected by addition of anti-TLR2 antibody to monocyte cultures. Therefore, signaling through the TLR2 receptor appears to play a role in phagosome trafficking and antimicrobial responses in MAP-infected bovine mononuclear phagocytes.

Mycobacterium avium subsp. paratuberculosis (MAP), the agent of paratuberculosis, is a slow growing mycobacteria that survives within ruminant mononuclear phagocytes by preventing cell activation and phagosome maturation. We investigated interactions between MAP and monocyte membrane receptors that result in activation of the mitogen-activated protein kinase (MAPK) p38 pathway and suppression of monocyte antimicrobial activity. Bovine monocytes were treated with blocking antibodies or specific chemical inhibitors of toll-like receptor 2 (TLR2), CD14 and CR3 receptor before infection with MAP organisms. MAPKp38 pathway activation, IL-10 expression and production, phagosome acidification, and MAP survival were determined. Our results indicated that MAP organisms-induced MAPKp38 activation occurs through partial interaction with TLR2. Blocking TLR2 receptors decreased IL-10 mRNA expression but not IL-10 protein production, increased phagosome acidification, and increased the capacity of monocytes to kill MAP organisms. Furthermore, blocking CR3 receptors increased phagosome acidification but did not alter MAP killing. These finding suggest that phagosome acidification is dependent on a complex interaction between MAP and the phagosome wall that may involve multiple receptors but that organism killing is dependent on specific signaling involving TLR2 receptors.

OBJECTIVETo determine cell membrane receptors involved in phagocytosis of Mycobacterium avium subsp paratuberculosis (MAP) organisms.SAMPLE POPULATIONMonocytes were obtained from healthy adult Holstein dairy cows that were test negative for MAP infection on the basis of bacteriologic culture of feces and serologic test results.PROCEDURESMonocytes or bovine macrophage cell line (BoMac) cells were incubated with MAP organisms for 30, 60, or 120 minutes with or without inhibitors of integrins, CD14, or mannose receptors. Phagocytosis was evaluated by light microscopy or by flow cytometry. CD11a/CD18, CD11b, and CD14 expression on monocytes and BoMac cells was evaluated by use of flow cytometry.RESULTSMonocytes and BoMac cells rapidly phagocytized MAP organisms. However, compared with BoMac cells, monocytes had a greater total capacity to phagocytize MAP organisms. Addition of neutralizing anti-integrin antibodies (anti-CD11a/CD18 and anti-CD11b) substantially inhibited phagocytosis by monocytes during the first 60 minutes of incubation with MAP organisms, but were less effective at 120 minutes of incubation. Anti-CD11a/CD18 and anti-CD11b antibodies were less effective in inhibiting phagocytosis by BoMac cells. Addition of inhibitors of CD14 or mannose receptors also inhibited phagocytosis of MAP by monocytes. Addition of a combination of integrin and mannose inhibitors had an additive effect in reducing phagocytosis, but addition of integrin and CD14 inhibitors did not have an additive effect.CONCLUSIONS AND CLINICAL RELEVANCEMultiple receptors are involved in phagocytosis of MAP organisms. Although CD11/CD18 receptors appear to be the major receptors used by MAP at early time points, mannose receptors and CD14 also contribute substantially to phagocytosis.

OBJECTIVE:To evaluate the role of the mitogen-activated protein kinase extracellular signal-regulated kinase (MAPK(ERK)) pathway in the interaction between Mycobacterium avium subsp paratuberculosis (MAP) organisms and bovine monocytes.SAMPLE POPULATION:Monocytes obtained from healthy adult Holstein dairy cows that were not infected with MAP organisms.PROCEDURES:Monocytes and MAP organisms were incubated together with or without a specific inhibitor of the MAPK(ERK) pathway (PD98059), and the capacity of monocytes to express tumor necrosis factor alpha (TNF)-alpha and interleukin (IL)-10 and -12, produce nitric oxide, acidify phagosomes, kill MAP organisms, and undergo apoptosis was evaluated.RESULTS:The MAPK(ERK) pathway was activated within 10 minutes after addition of MAP organisms to monocytes. Addition of PD98059 to monocyte-MAP mixtures decreased monocyte TNF-alpha and IL-12 mRNA expression but had no effect on IL-10 mRNA expression. Treatment with PD98059 failed to induce significant alterations in phagosome acidification, organism killing, nitric oxide production, or apoptosis of MAP-exposed monocytes.CONCLUSIONS AND CLINICAL RELEVANCE:Results indicated that the MAPK(ERK) pathway was activated during the interaction of MAP organisms with monocytes, which initiated TNF-alpha and IL-12 mRNA expression but failed to initiate antimicrobial activity. The MAPK(ERK) pathway may be involved in initiating proinflammatory and proimmune responses in MAP infection in cattle.

We compared the kinetics of activation and antimicrobial activities of MAPK-p38 and MAPK-ERK in bovine monocytes infected with Mycobacterium avium subsp. paratuberculosis (MAP) and Mycobacterium avium subsp. avium (Maa). Monocytes were incubated with MAP or Maa organisms with or without a specific inhibitor of the MAPK-p38 pathway (SB203580), and MAPK phosphorylation and antimicrobial functions of monocytes were evaluated. At early time points MAPK-p38 phosphorylation was greater in MAP-infected bovine monocytes than in Maa-infected monocytes. At later time points MAPK-p38 phosphorylation by both organisms was similar. MAPKp38 phosphorylation in MAP-infected monocytes was similar to negative control cells, whereas in Maa-infected this activation remained greater than negative control cells. Increase phosphorylation MAPK-ERK was similar at all time points for both organisms. Bovine monocytes had minimal capacity to kill MAP organisms, to acidify MAP-containing phagosomes, or to form phagolysosome. Alternatively, bovine monocytes were able to kill Maa organisms. Addition of SB203580 to monocyte cultures increased phagosome acidification, phagolysosome formation, and killing of MAP and Maa organisms. Taken together these data indicate that early transient activation of MAPK-p38 in bovine mononuclear phagocytes by MAP organisms may be a key mechanism involved in the capacity of MAP to survive in bovine monocytes.

Objective-To evaluate activation of Jun N-terminal kinase/stress-activated protein kinase (JNK/SAPK) pathway in bovine monocytes after incubation with Mycobacterium avium subsp paratuberculosis (Mptb) organisms.Sample Population-Bovine monocytes obtained from 4 healthy adult Holstein dairy cows.Procedures-Bovine monocytes were incubated with Mptb organisms with or without a specific inhibitor of the JNK/SAPK pathway (SP600125) for 2, 6, 24, or 72 hours. Expression of interleukin (IL)-1 beta, IL-10, IL-12, IL-18; transforming growth factor-beta (TGF-beta); and tumor necrosis factor-alpha (TNF-alpha) and the capacity of Mptb-infected monocytes to acidify phagosomes and kill Mptb organisms were evaluated. Phosphorylation status of JNK/SAPK was evaluated at 10, 30, and 60 minutes after Mptb incubation.Results-Compared with uninfected control monocytes, Mptb-infected monocytes had increased expression of IL-10 at 2 and 6 hours after incubation and had increased expression of TNF-alpha, IL-1 beta, IL-18, and TGF-beta at 2, 4, and 6 hours. Additionally, Mptb-infected monocytes had increased expression of IL-12 at 6 and 24 hours. Addition of SP600125 (specific chemical inhibitor of JNK/SAPK) resulted in a decrease in TNF-a expression at 2, 6, and 24 hours, compared with untreated Mptb-infected cells. Addition of SP600125 resulted in a decrease in TGF-beta expression at 24 hours and an increase in IL-18 expression at 6 hours. Addition of SP600125 failed to alter phagosome acidification but did enhance the capacity of monocytes to kill Mptb organisms.Conclusions and Clinical Relevance-Activation of JNK/SAPK may be an important mechanism used by Mptb to regulate cytokine expression in bovine monocytes for survival and to alter inflammatory and immune responses.

We investigated the role of cell signaling through the mitogen-activated protein kinase-p38 (MAPK p38) pathway on the antimicrobial functions and cytokine expression by bovine monocytes after ingestion of Mycobacterium avium subsp. paratuberculosis. We evaluated the dynamic secretion of interleukin (IL)-10, IL-12 and tumor necrosis factor-alpha (TNF-alpha) as well as phagosome acidification and organism killing at several time points after in vitro infection of bovine monocytes with M. avium subsp. paratuberculosis. Monocytes treated with M. avium subsp. paratuberculosis had a significant increase in IL-10 expression at 2, 4, and 6h post-infection and an increase expression of TNF-alpha at 2, 4, 6, and 24h post-infection. In contrast, IL-12 expression did not increase at any time point post-infection. Moreover, MAPK p38 was rapidly phosphorylated at 10 and 60 min after M. avium subsp. paratuberculosis ingestion. Chemical inhibition of the MAPK p38 signaling pathway (SB203580) resulted in decreased expression of IL-10 and increased expression of IL-12 at 6h post-infection. Chemically blocking the MAPK p38 pathway also increased acidification of phagosomes as well as increasing the capacity of macrophages to kill organisms. Taken together, these results indicated that selective activation of MAPK p38 may be a major mechanism exploited by M. avium subsp. paratuberculosis to circumvent the antimycobacterial effects of mononuclear phagocytes.

OBJECTIVE:To determine the capacity of inflammatory mediators tumor necrosis factor-alpha (TNF-alpha), interleukin-8 (IL-8), platelet-activating factor (PAF), lipopolysaccharide (LPS), and leukotoxin to prime, activate, or alter deformability of adult bovine neutrophils.SAMPLE POPULATION:Blood collected from 5 healthy adult Holstein cows.PROCEDURE:Isolated neutrophils or whole blood was incubated with TNF-alpha, IL-8, PAF, LPS, or leukotoxin, and neutrophil chemiluminescence, degranulation, deformability, shape change, CD11b expression, and size distribution was measured.RESULTS:Incubation with TNF-alpha, IL-8, PAF, and LPS primed neutrophils for oxygen radical release but caused minimal oxygen radical release by themselves. None of the inflammatory mediators induced degranulation. Incubation with TNF-alpha and PAF resulted in a decrease in neutrophil deformability and induced shape change in neutrophils. Incubation with PAF consistently resulted in an increase in neutrophil size as measured by use of flow cytometry. Only IL-8 caused an increase in expression of CD11b by neutrophils.CONCLUSIONS AND CLINICAL RELEVANCE:Inflammatory mediators tested had minimal effects on neutrophil oxygen radical production or degranulation but did prime neutrophils for oxygen radical production. Incubation with PAF and TNF-alpha caused a decrease in neutrophil deformability and altered neutrophil shape and size. Results of our study indicate that PAF- and TNF-alpha-induced changes in neutrophil deformability and size may cause integrin- and selectin-independent trapping of neutrophils in the lungs of cattle with pneumonic pasteurellosis.

The filterability of equine RBC and whole blood was evaluated to better understanding the effects of exercise-associated haemoconcentration and increased cardiac output on the flow properties of blood in the microvasculature. When RBC were filtered through filters with 3 µm pores (3 µm filters), the initial increase in filtration pressure (Pi) increased 4.6-fold between packed cell volumes (PCV) of 5% and 40%. Filters with 5 µm pores had lower Pi at all PCV studied and the absolute increase in Pi with increasing PCV was minimal. Increasing the flow rate resulted in marked increases in Pi for 3 µm filters. The Pi for 5 µm filters also increased with increasing flow rate but values were consistently less than for 3 µm filters. The Pi values for horse RBC were less than those for human RBC at all flow rates evaluated. Calculated wall shear stress values were much higher for 3 µm filters than those for 5 µm filters. Filtration pressures and wall shear stress values for whole blood were greater than those for RBC for both 3 µm and 5 µm filters. These data suggest that changes in PCV and flow rate may significantly alter shear forces in the microvasculature particularly in vessels approaching 3 µm in diameter.