[Antibodies in systemic autoimmune diseases. Special mention to systemic lupus erythematosus]

Autoantibodies are the expression of humoral response to self-antigens and they may be diagnostic of autoimmune diseases. Studies in systemic lupus erythematosus (SLE) have shown that autoantibodies react with macromolecular structures such as the nucleosome or the spliceosome. These self-antigens are complexes of protein-DNA or protein-RNA like those recognized by anti-dsDNA or anti-RNPs (U1, Sm, Ro, La) antibodies respectively. Recent knowledge on innate immunity has shed more light on the pathological role of these autoantibodies. The antigen-antibody complexes formed as the result of an increase of sel-antigens in the blood as a consequence of an increase in apoptosis, attach to dendritic FcγII or B cell receptors. Through the attachment to the receptor, the macrocomplex is internalized within the cell and recognized in the endosomic membranes by receptors of the innate immune system named TLR (Toll-like receptor). There are at least 13 TLRs localized either in the cellular or the endosomic membranes. Of the latter group, TLR-7 is specific for ssRNA, and TLR-9 is specific for CpG DNA. The reaction of the immunocomplexes with the receptor triggers a kinase cascade that leads to IFNα production. The IFNα is a molecule of the innate and adaptative immune system responsible for the immune deregulation and pathological signs in the SLE. It plays an important role in antigen presentation to the autoreactive quiescent autoreactive T cells and in increasing the life span of dendritic and B cells. In addition, the increase in self-antigens released by greater apoptosis enhances the production of autoantibodies and their effect on the increase of IFNα production.