ANTIBODIES AGAINST MESANGIAL CELLS AND THEIR SECRETORY PRODUCTS IN CHRONIC RENAL-ALLOGRAFT REJECTION IN THE RAT

Antibodies or cell-mediated immunity can cause chronic rejection of va scularized organ grafts, but the nature and specificity of the antigen (s) involved has remained elusive. We have previously demonstrated the presence of antibodies against cryptic glomerular basement membrane a ntigens and undefined antigens in the mesangial area in rats with chro nic renal allograft rejection. Current experiments were designed to st udy the post-transplant antibody response against cultured mesangial a nd endothelial cells in rats with chronic rejection using flow cytomet ry, indirect immunofluorescent staining, immunoelectron microscopy, co nfocal microscopy, and Western blots. The results were compared with t hose obtained with alloantisera raised by immunization with cultured m esangial cells. Post-transplant and post-immunization sera contained I gG antibodies against trypsinized mesangial cells detected by flow cyt ometry. Indirect immunofluorescent studies using mesangial cells grown on coverslips showed autoantibody binding to cytoplasmic granules in cultures early after plating whereas staining of later cultures showed antibody binding in an interrupted, web-like pattern on the outside o f the cells. Immunoelectron microscopy showed autoantibody binding to intracellular secretory granules and to cell surface focal adhesion pl aques. The latter finding was confirmed in double-labeling experiments with an antiserum against vinculin. Western blots with mesangial cell culture supernatants demonstrated autoantibody reactivity with antige ns in the 40-kd and 60- to 70-kd range, and immunoprecipitation identi fied these molecules as biglycan and decorin. Absorption of the sera w ith mesangial cell culture supernatant removed most of the antibodies except those that gave a punctate staining with the mesangial cell sur face. However, not all immunostaining of mesangial cells could be expl ained by antibodies against biglycan and decorin. Post-transplant sera , furthermore, contained low-titered antibodies against endothelial ce lls. We conclude that rats with chronic renal transplant rejection pro duce a strong autoantibody response against mesangial cell focal adhes ion plaques and proteins secreted by these cells in culture. Such anti bodies may cause local damage and interfere in the tissue repair proce ss after injury.