IgE production after antigen-specific and cognate activation of HLA-DPw4-restricted T-cell clones, by 78% of randomly selected B-cell donors.

The frequency of expression of the MHC class II antigen, HLA-DPw4, in the caucasoid population is approximately 78%, and is unmatched by phenotypic frequencies of other HLA class II molecules. Here we describe three human Der-P1-specific T-cell clones (TCC), restricted by the HLA-DPw4-variant HLA-DPB1*0401, of which two TCC also responded to antigen, presented on HLA-DPB1*0402. Thus, randomly selected caucasoid donors present a 78% chance for a correct match with these HLA-DPw4-restricted TCC. This allows comparative in vitro antigen presentation studies with various antigen presenting cells (APC) from different (healthy or diseased) donors without the variable influence of responding T cells. It was subsequently demonstrated that the TCC can be used to study antigen-induced IgE production in randomly selected primary B cells. Cognate HLA-DPw4-restricted antigen presentation caused enhanced immunoglobulin production of IgE, IgG1, IgA and IgM, of which only IgE induction was reversed by addition of anti-IL-4 antibodies.

The 'monocytic' cell line I937 displays typical B cell characteristics.

The monocytic cell line I937 was derived from U937 by sorting for cells with high expression of MHC class II molecules. Further analysis of these class II molecules revealed the presence of the HLA-DR3 subtype suggesting that the cell line was a potential candidate for testing antigen presentation to T cells restricted by HLA-DR3. We found that the T cell clones CFTS4:2.80 and CFTS4:2.6 with the required restriction element responded to the house dust mite antigen DPT presented by I937 but not U937, whereas CFTS4:3.1, which is not HLA-DR restricted, did not respond to either cell line. Subsequent analysis of surface markers on I937, however, indicated that the cell line is of B cell origin. In contrast to the parental cell line U937, I937 was tested negative for CD4, CD31 and CD64 but expressed CD19, CD21 and CD40. Although neither surface nor cytoplasmic Ig molecules were detected in either I937 or U937, Southern blot analysis revealed IgH gene rearrangement in I937. In addition, a fragment specific for Epstein-Barr virus nuclear antigen (EBNA2) was amplified in I937 by PCR technique. Therefore, we conclude that I937 is an EBV-transformed B cell line, presumably derived from the same donor and not as reported originally as a subline of U937, which expresses high MHC class II levels.