Characterization of a monoclonal antibody recognizing a polymorphic epitope mainly on HLA‐DPw2 and DPw4 molecules

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Abstract
A monoclonal antibody (MAb), 13.3.B4, was obtained from a murine hybridoma after fusing Sp2/0 myeloma cells with spleen cells from C3H mice immunized with mouse L cells transfected with the A1 and B1 genes of HLA-DPw4. In radiobinding-assays, MAb 13.3.B4 bound to HLA transfectants expressing DPw2 or DPw4 as well as DPw2 or DPw4 homozygous B-cell lines, while most cell lines expressing other DP determinants were negative. MAbs with known DP or other HLA class II-specificities were used to inhibit binding of MAb 13.3.B4 in a radioimmunoassay. Three MAbs demonstrated inhibition, but their pattern of reactivity with HLA homozygous B cell lines differed from that of MAb 13.3.B4. An evaluation of DNA sequence data showed that MAb 13.3.B4 reacts with all cell lines expressing DP .beta.-chains of type 2.1, 2.2, 4.1 or 4.2. No correlation between 13.3-B4-reactivity and expression of DP .alpha.-chain variants was found. The results indicate that MAb 13.3.B4 defines a polymorphic epitope which may be determined by the sequence gly-gly-pro-met at residues 84-87 and the DP .beta.-chain.