Soluble factor(s) from LPS-activated macrophages induce cytotoxic T cell differentiation from alloantigen-primed spleen cells.

Abstract

Spleen cells obtained from mice 2 to 3 months after alloantigen-priming generated cytotoxic responses when cultured with supernatants from lipopolysaccha-ride- (LPS) activated peritoneal exudate adherent cells (PEAC). The cytotoxic response was mediated by T cells, and was specific for the priming alloantigen. Spleen cells from unprimed mice failed to generate cytotoxicity when similarly cultured.A number of experimental approaches suggested that the factor(s) were produced by LPS-activated macrophages. These included the observations that: 1) the factor(s) were produced by PEAC from which B cells and T cells had been depleted, 2) PEAC from nude mice produced these factors. In all cases, LPS activation was necessary for the effects noted, since supernatants from PEAC cultured in the absence of LPS failed to induce cytotoxic responses. Furthermore, stimulation of PEAC from LPS-unresponsive C3H/HeJ mice did not lead to factor production, whereas PEAC from LPS-responsive C3H/HeN mice did so.Supernatants from cultures of LPS-activated PEAC were shown to be mitogenic for memory splenic T cells, as assayed by 3H-thymidine incorporation. However, the cytotoxic response induced by these supernatants was not dependent upon spleen cell proliferation. Mitomycin C-treated memory spleen cell populations generated equivalent levels of cytotoxic activity after culture with LPS-activated PEAC supernatants, as did cells not exposed to the drug.The ability of spleen cells to be stimulated by supernatants from LPS-activated PEAC was present only for a limited time interval after in vivo priming with alloantigen. Spleen cells taken from mice 6 months post-alloan-tigen priming gave a vigorous cytotoxic response after culture with the priming alloantigen, but they did not respond to the LPS-induced supernatants. This indicates that the responding cell is relatively short lived and that cytotoxic memory responses may involve different functional T cell populations at varying times post-alloanti-gen priming.