HUMAN MONOCLONAL-ANTIBODY WITH T-CELL-LIKE SPECIFICITY RECOGNIZES MHCCLASS-I SELF-PEPTIDE PRESENTED BY HLA-DR1 ON ACTIVATED CELLS

Alloreactive T cells recognize peptides presented in the binding groov e of major histocompatibility complex molecules (MHCs) whereas B cells mainly recognize the MHCs independent of bound peptides. Here, we dem onstrate that the human B-cell repertoire comprises B cells which can be stimulated during pregnancy to produce antibodies reacting with MHC s in a way similar to T cells The human monoclonal antibody UL-5A1 rec ognizes DR1(DRA/DRB10101) molecules on lymphoblastoid cell lines only if they coexpress HLA-A2 or ii they have been loaded with HLA-A2-deri ved peptides The effect of the HLA-A2 peptide 105-117 on UL-5A1 reacti vity was specific, time and dose-dependent. Reactivity increased when naturally processed peptides were removed from DR1 molecules before th e HLA-A2 peptide 105-117 was loaded. UL-5A1 reacted specifically with cells that had been activated. The results imply a role of activation of cells in peptide processing and/or loading.