Differential effect of cholera toxin on CD45RA+ and CD45RO+ T cells:: specific inhibition of cytokine production but not proliferation of human naive T cells

We have studied how cholera toxin (CT) and its non-toxic cell-binding B-subunit (CTB) affect the activation of pure human T cells in an anti-CD3-driven system. CT, as opposed to CTB, strongly suppressed the proliferative responses as well as cytokine production in CD4(+) and CD8(+) T cells. CT however, had a differential effect on naive and activated/memory T cell subsets. Costimulation through exogenous IL-2 or through CD28 cross-linking rescued the proliferation of CT-treated naive CD45RA(+) T cells, but not of activated/memory CD45RO(+) cells. IL-2 production and IL-2 receptor expression were markedly reduced by CT in all T cell fractions, i.e. also in CD45RA(+) cells which had maintained proliferative responses. However, the proliferative responses of CT-treated CD45RA(+) T cells were IL-2-dependent, as shown by blocking experiments using anti-IL-2 antibodies. These results indicate (i) that CTB has no cytostatic effect on human T cells, (ii) that CT affects proliferation and cytokine production by two different signal pathways, and (iii) that CT might interact with a signal pathway generated through or influenced by CD45.