Role of CD40 antigen and interleukin‐2 in T cell‐dependent human B lymphocyte growth

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Abstract
In the present study, we examined the participation of CD40 ligand (L)‐CD40 interaction in T cell‐dependent B cell responses. To this end, purified B lymphocytes were cultured over irradiated CD4+ cloned T cells activated with immobilized anti‐CD3 antibody. The anti‐CD40 mAb 89 strongly blocked, in a specific fashion, both proliferation and Ig secretion of tonsil B cells. Interestingly, proliferation of surface (s)IgD+ B cell was significantly less inhibited by anti‐CD40 than that of sIgD− cells. Preactivated T cells induced B cells to grow and secrete immunoglobulins preferentially in response to IL‐2. This contrasts with the CD40 system where B cells are essentially responsive to IL‐4 and IL‐10 but not to IL‐2 alone. Collectively, these data indicate that CD40L‐CD40 interaction plays an important role in IL‐2‐mediated T cell‐dependent B cell responses. However, the activation of a subset of sIgD+ cells may be independent of this interaction.