The monoclonal antibodies 7.3.19.1 (anti-DRw52-like) and B8.11.2 (anti-DR framework) were used for the isolation and characterization of HLA class II molecules expressed by HLA-DR3 and DR5 homozygous ...B cell lines. Sequential immunoprecipitation studies demonstrated that from these cells class II molecules can be isolated which are characterized by the presence or absence of DR framework (DR) and DRw52-like (DRw62) determinants: (DR+, DRw52+), (DR+, DRw52-) and (DR-, DRw52+). The DR3 donor cells appeared to express only the (DR+, DRw52+) and (DR-, DRw52+) class II molecules whereas DR5-positive cells express only the (DR+, DRw52+) and (DR+, DRw52-) class II molecules. Besides qualitative differences some of the above-mentioned molecules appeared to differ in their levels of expression. To investigate whether this might have functional implications, cells with the HLA-DR3 and -5 haplotypes were used to present antigen purified protein derivative of tuberculin (PPD) to PPD-specific T cell lines and the blocking capacity of the two monoclonal antibodies 7.3.19.1 and B8.11.2 was determined. A remarkable correlation was observed between the type of class II molecule blocked by these monoclonal antibodies and its quantitative expression. However, (DR-, DRw52+) molecules, clearly expressed by DR3 cells, were not involved in the presentation of PPD. This indicates that not only quantitative but also qualitative aspects may play a role in the selection of the type of class II molecule that will be involved in antigen presentation.
