RESUMO
Despite all advances, kidney transplant specialists still face a common problem sometimes very hard to solve: the immunologic rejection. Generally classified in hyperacute, acute and chronic, the role of antibodies as mediators is clear in some cases and controversial in other. The main type is the hyperacute, which arises from an injury to graft vascular endothelial cells mediated by anti-donor HLA class-I antibodies (IgG) or anti-ABQ (IgG and/or IgM). HLA molecules comprises three main classes: class-I (mainly HLA-A, B and C), found on virtually all nucleated cells, class-II (mainly HLA-DR, DQ and DP), whose expression is confined basically to immunocompetent cells, and class-III, which includes some complement subunits, tumor necrosis factor and heat shock proteins. HLA molecules are expressed also in renal tissue. Anti-HLA antibodies are produced in response to blood transfusions, pregnancy or rejection of a previous transplant. From this knowledge, it was introduced the first immunogenetic test in kidney transplantation routine (the crossmatch) in which the patient serum samples are reacted with donor cells before surgery. Some patients, although giving a negative crossmatch ("absence" of anti-donor antibodies in the crossmatch test), lose their grafts. Some of these cases were correlated to anti-donor vascular endothelial cells, and reacted also with keratynocytes in skin sections, through immunofluorescence, with high titles. Such skin crossmatch seems to be predictive of rejection in more then 70 percent of the cases. Studyng aloatisera from patients previously exposed to various stimuli that normally induce HLA sensitization, we concluded that skin crossmatch can give false-positive reactions. Many strategies have been used to overcome the humoral barrier. One of the first was the spleenectomy, which represented a landmark in the improvement of the graft follow-up in the pre-ciclosporine era. During the following years, its beneficial effect was completely disguised, but few special recent protocols still include this procedure. Another strategy employed was the non-specific depletion of antibodies from the circulation, which can be done by plasmapheresis or immunoadsorption. Until now, it does not exist the ideal crossmatch, that is 100 percent sensible and 100 percent specific...