Cellular Expression or Binding of desLys58‐β2 Microglobulin is not Dependent on the Presence of the Tri‐molecular MHC Class I Complex

The monoclonal antibody 332-01 is a newly developed antibody which specifically recognizes human desLys58-b2 microglobulin (db2m). In the present study, we characterized the binding of 332-01 to peripheral blood mononuclear cells (PBMC), a number of human leukaemic and monocytic cell lines, and b2m gene-deleted murine lymphocytes. db2m was found to be expressed on non-activated and activated monocytes. When cells were pre-exposed to db2m, 332-01 also bound to non-activated T lymphocytes. db2m was expressed on the monocytic cell lines U937 and TIB-202, and binding was significantly increased when cells were pre-incubated with db2m and when TIB-202 cells were exposed to lipopolysaccharide. db2m was also expressed on T leukaemic Jurkat cells as well as on low HLA-expressing erythroleukaemic K562 cells. b2m gene-deleted murine splenocytes only bound 332-01 after pre-exposure to db2m. Binding of 332-01 antibody could not be displaced by addition of high concentrations of native b2m. In conclusion, our data indicate that db2m – in contrast to native b2m – binds to a hitherto unknown cell surface receptor independent of classical MHC class I molecules. As b2m has previously been shown to display biological activities such as the induction of both growth promotion and apoptosis, C1 complement activity, shown to mediate cleavage of b2m, could be involved in these processes.