In over one century of research in immunology marked progress in the scientific knowledge and the implications derived from it has been made. At the same time several contradictory and seemingly opposing results have been obtained. The term autoimmunity is still conceived by many as a term directly related to an immunopathological state. However, strong evidence exist that not only the immune system is able to recognize self-constituents, but it appears also that this property is essential for homeostasis. Direct or indirect alterations of such self-recognition properties of the immune system may contribute to pathology. In this review, the most recent advances in the field of naturally occurring B-cell autoreactivity in health as well as in disease are presented and discussed.

Interleukin-1 receptor (IL-1R) deficiency has been previously described in the dentate gyrus of autoimmune NZB and (NZB×NZW) F1 (or BWF1) mice. In this study, the genetic and molecular characterization of this defect were investigated in BWF2 mice in relation to anti-DNA antibody production and microsatellite D1Nds4 (near the IL1r1 gene) polymorphism. IL-1R density was quantified in the brain, spleen and pancreas, using in vitro quantitative autoradiography with recombinant human [125I]-IL-1α as the ligand. This study of the dentate gyrus of F2 mice revealed three phenotypes: NZW-like, NZB-like and F1-like, which occurred in a ratio of 1:1:2, with IL-1R densities of 100%, 17% and 59%, respectively as compared to control NZW mice (100%). In contrast, IL-1R densities observed in the choroid plexus and peripheral organs were similar. Moreover a high production of IgG2a anti-DNA antibodies was observed in F2 mice, as in their parents, particularly those with the NZB-like phenotype. Microsatellite mapping of D1Nds4 revealed polymorphism in both parents and BWF2 mice in relation to the level of lL-1R density in the dentate gyrus. In spite of the acute defect in IL-1 binding in the dentate gyrus of NZB mice, molecular analysis of IL-1R mRNA (type I, II and accessory protein) showed similar amounts of mRNA, measured following RT-PCR amplification, in the hippocampal formation of both NZB and control C3H/He mice. In conclusion, the transmission of the IL-1R defect in the dentate gyrus of NZB mice is monofactorial and the defect appears to be at the post-transcriptional level of IL-1R synthesis. The lack of IL-1R in the dentate gyrus seems to correlate with some autoimmune characteristics. Correlation of D1Nds4 polymorphism with the level of IL-1R density suggests that it could be a predisposing gene to disease or a marker for other closely linked predisposing genes.

Many monoclonal antibodies (mAb) derived from the spleens of (NZBxNZW)F1 mice react strongly with dsDNA and also other self antigens, although more weakly. When added to cell cultures, these polyreactive anti-DNA mAb penetrate into various cell types and accumulate in the nucleus within a few hours. Almost all anti-DNA mAb bind to cell membrane antigens but the extent of their binding does not directly correspond to their penetration capabilities. Sequence analysis of anti-DNA mAb indicated the use of various germ-line VH families. The complementary-determining regions (CDR) 3 differ but they all contain a relatively high number of tyrosines and positively charged amino acids (lysine and arginine). Haptens (biotin, fluor-escein, oligonucleotides) and macromolecules (peroxidase, IgG) covalently coupled to the mAb or their F(ab')2 and Fab fragments were translocated through the cytoplasm and into the cell nucleus. Furthermore, 61% of peripheral blood lymphocytes were labelled when mice were injected with fluorescein-labelled mAb. Peptides corresponding to CDR2, CDR3 and CDR2 linked to CDR3 (CDR2-3) of several penetrating mAb were prepared and their intracellular translocating capacity was assessed. The CDR2-3 peptide, but not the individual peptides, was able to penetrate cells and could be used as a vector to transport macromolecules. Although all CDR2-3 reacted with dsDNA and other self antigens, each one exhibited a distinct polyreactivity profile.

Different studies have shown that some autoantibodies are able to penetrate into living cells and that this phenomenon has functional consequences, including apoptosis. We have explored the effect of anti-DNA antibodies (Ab) on the in vitro activation of peripheral blood mononuclear cells (PBMNC) and found that a human polyclonal anti-DNA, IgG, which efficiently penetrated living cells, was able to induce the expression of different cell activation antigens in vitro such as CD69, CD71 or CD98 by PBMNC from normal individuals. However, the cell activation phenotype induced by anti-DNA Ab was considered anomalous since the expression of some activation antigens was not up-regulated, and others showed aberrant behaviour (such as down-regulation of ICAM-1 expression). Similar results were obtained using different murine anti-DNA monoclonal antibodies (mAb). In addition, mAb that showed an efficient ability to penetrate living cells tended to have a greater effect on PBMNC activation. Anti-DNA Ab were also able to induce a noticeable expression of CD95/Fas. These data indicate that penetrating anti-DNA Ab are able to induce an anomalous activation state in vitro in a significant fraction of PBMNC. We believe this effect may occur in vivoand could have an important function in the pathogenesis of the immune dysregulation seen in SLE.

Interleukin-1 receptors (IL-1R type I and II) have been characterized in murine nervous structures (hippocampus and frontal cortex), in vascular structures (vessels, choroid plexus), and in the anterior pituitary. Because interleukin-1 (IL-1), injected or induced in the brain, is a powerful regulator of the stress axis and immune functions, it was of interest to investigate IL-1Rs and IL-1 in autoimmune mice. In control mice, bacterial lipopolysaccharide (LPS), administered i.p. or i.c.v., induces a sharp decrease in available brain IL-1 receptors, in spite of a moderate increase in mRNAs for both receptor types. This is concomitant with an increase in IL-1 alpha, beta, and ra mRNA. Ligand production clearly overcomes receptor turnover. In autoimmune mice (NZB and NZB/NZW F1), a strong defect in IL-1R (type I) is demonstrated in the dentate gyrus. This tissue-specific defect cannot be explained by increased occupancy by endogeneous ligands as for LPS-treated mice. The transmission of the defect is Mendelian and suggests the involvement of a single gene. However patterns of IL-1R mRNAs (evaluated by RT-PCR) are similar in NZB and in controls, suggesting a translational or post-translational abnormality. The contribution of this genetic disorder in the development of autoimmunity remains to be clarified. Because the brain IL-1 system sends inhibitory signals towards immune functions, this lack of functional IL-1 binding sites might participate in the disregulations observed in NZB autoimmune mice.

Naturally occurring polyreactive anti-DNA mAbs derived from a nonimmunized (NZB x NZW) F-1 mouse with spontaneous lupus erythematosus penetrated and accumulated in the nuclei of a variety of cultured cells. These mAbs and their F(ab')2 and Fab' fragments, covalently coupled to fluorescein, peroxidase, or a 15-mer polynucleotide, also translocated to the cell nuclei, A 30-amino acid peptide corresponding to the combined sequences of the complementary-determining regions 2 and 3 of the heavy chain variable region of one mAb was able to penetrate into the cytoplasm and nucleus of cells of several lines. This peptide recognized DNA and was strongly polyreactive, Streptavidin-peroxidase conjugates complexed with the N-biotinylated peptide were rapidly translocated into cells. Similarly, peroxidase or anti-peroxidase polyclonal antibodies covalently coupled to the N-cysteinylated peptide through an heterobifunctional maleimide cross-linker were also rapidly internalized and frequently accumulated in nuclei, The peptide carrying 19 lysine residues at its N-terminal was highly effective in transfecting 3T3 cells with a plasmid containing the luciferase gene. Thus, penetrating mAbs and derived peptides are versatile vectors for the intracellular delivery of proteins and genes.