Effects of phorbol myristate and ionomycin on in vitro growth of aged Peyer's patch T and B cells.

The proliferative responses of Peyer's patch (PP) T cells from aged BALB/c mice to concanavalin A (Con A) are considerably reduced, as compared to those of the young (P < 0.001). This reduced reactivity of aged T cells could be partly, but not entirely, corrected by interleukin 2 (IL-2) (P < 0.001). PP T cells from aged mice responded synergistically to a protein kinase C (PKC) activator, phorbol myristate acetate (PHA), plus a calcium ionophore, ionomycin, at much lower concentrations than to Con A (P < 0.001); however, the maximal proliferative response still remained nearly at 8/10th of the young (P < 0.01) and higher levels of PMA (but not of ionomycin) were required (P < 0.001). Addition of IL-2 restored the diminished response to the levels of the young T cells (P < 0.05), but that of Con A did not (P > 0.05). The proliferative responses of PP B cells to lipopolysaccharide (LPS) do not differ from those of the young (P > 0.05), but the spontaneous proliferation of aged (unstimulated) B cells is enhanced nearly twofold versus that of the young (P < 0.001). Like the PP T cells, PP B cells from aged mice also responded synergistically to PMA plus ionomycin but to a lesser degree than those of the young under the same stimulation (P < 0.01). Their maximal proliferation required higher levels of PMA, but not of ionomycin and was also diminished (P < 0.01), compared to that of the young. B cell stimulatory co-factors, IL-4 and IL-6, failed to affect the response of aged and young B cells to PMA plus ionomycin (P > 0.05), whereas LPS remediates the reduced response of aged B cells to PMA plus ionomycin. Thus, T and B cells from senescent PP demonstrate an impaired proliferative responsiveness via the Ca-dependent PKC pathway. A T cell mitogen and B cell stimulatory cytokines did not alter this activation pathway, once optimally stimulated. Whereas, T cell stimulatory cytokine IL-2 and B cell mitogen LPS could restore the age-associated decline of the corresponding lymphocyte subsets, T and B cells, in activation of the Ca-dependent pathway. The altered transmembrane signal transduction appears to be intrinsically defective in these aged PP T and B cells.