CD23 CD21 INTERACTION IS REQUIRED FOR PRESENTATION OF SOLUBLE-PROTEINANTIGEN BY LYMPHOBLASTOID B-CELL LINES TO SPECIFIC CD4(+) T-CELL CLONES/

Previous studies have documented a role for membrane-bound CD23 (the l ow affinity Fc epsilon RII) in presentation of alloantigens by B cells . The aim of the present study was to examine the involvement of cell surface CD23 in presentation of more conventional soluble protein anti gens to T cells. We show that antibodies to CD23 and to its lymphocyte -associated second ligand, CD21, inhibit presentation of the cow's mil k allergen casein, by autologous CD23(+) CD21(+) B-EBV cell Lines to c asein-specific HLA-DP-restricted CD4(+) T cell clones obtained from pa tients with either reaginic or enterophatic forms of cow's milk protei n intolerance. Maximal inhibition was achieved when the antibodies wer e added at the initiation of the culture. The absence of specific inhi bition by an anti-DR alpha monoclonal antibody (mAb) argues against a steric hindrance phenomenon impeding access of the T cell receptor to major histocompatibility complex class II molecules. Rather, anti-CD23 and anti-CD21. mAb-induced inhibition of antigen presentation seems t o affect at least partly, heterotypic conjugate formation through CD23 /CD21 interaction. Double immunofluorescence labeling of the T cell cl ones and antibody inhibition of T/B conjugate formation shows that fun ctional CD23 and CD21 molecules are induced on T cells following conta ct with B-EBV cell lines. Taken together, these data indicate that CD2 3/CD21 interactions between T and B cells are required for presentatio n of soluble protein antigens by B-EBV cell lines to specific CD4(+) T cells. The potential implications of these findings for allergen-spec ific T cell activation are discussed.