THE SERA FROM HIGHLY SENSITIZED PATIENTS CONTAINS A NON-HLA CLASS I ANTIBODY THAT STIMULATES B CELLS TO PRODUCE CYTOTOXIC HLA CLASS I ANTIBODIES

Abstract

137 The mechanism whereby highly sensitized patients (HSP) maintain antibodies against class I HLA antigens is unknown. To test the hypothesis that the sera of HSP contains an IgG which promotes anti-class I antibody production, IgG was isolated from the sera of each of 5 HSP (IgG, HS) whose PRA ranged from 80-100% for many years and was compared to IgG from normal pooled serum (IgG, N). Both IgG (HS) and IgG (N) were absorbed with platelets to eliminate antibodies to class I antigens as determined by ELISA and cytotoxicity assays. These preparations were also negative for HLA class I antigens as measured by immunostaining western blots with a monoclonal antibody recognizing a framework determinant residing on the heavy chain of the HLA class I antigen. We generated culture supernatants from B cells treated with purified, platelet absorbed immunoglobulins prepared from the serum of highly sensitized patients IgG (HS) or normals IgG (N). Supernatant resulting from B cells treated with IgG (HS) contained HLA class I antibodies as measured by ELISA and cytotoxicity assays (48.4±4.9% killing). Supernatant resulting from B cells treated with IgG (N) was negative for HLA class I antibodies as measured by ELISA and cytotoxicity assays. We further show that the cytotoxic antibodies could be eliminated/reduced by preincubation of the supernatant with IgG (HS, 6.0±3.8% killing) compared to preincubation with IgG (N, 55.0±23.2% killing). We conclude that there is an IgG in the sera of HSP which stimulates B cells to produce allogeneic anti-HLA antibodies. Furthermore these results suggest that this antibody is an anti-idiotype which stimulates B cells to produce anti-class I cytotoxic antibodies and may be responsible for the sustained anti-HLA response in highly sensitized patients.