The LT system in experimental animals. IV. Rapid specific lysis of 51CR-labeled allogeneic target cells by highly unstable high m.w. lymphotoxin-receptor complex(es) released in vitro by activated alloimmune murine T lymphocytes.

Abstract

Lymphocytes or purified T cells obtained from the spleens of alloimmune C57BL/6, DBA/2, or C3H/DiSn mice, when placed on monolayers of lectin-coated allogeneic (L-929 or 3T3) fibroblasts, release into the supernatant various forms of cell lytic material. One form appears to be a high m.w. complex containing an antigen-binding receptor(s) that is highly labile and capable of causing rapid and specific lysis of allogeneic target cells in vitro. Material(s) that could mediate these cell lytic effects were detected in culture supernatants as early as 3 hr after stimulation, peaked at 6 to 9 hr, and declined thereafter. The specific cell lytic activity appeared to be due to high m.w. LT-receptor complexes for the following reasons: (a) antisera that could neutralize murine LT activity in vitro could inhibit this effect; (b) absorption of supernatants on the specific target cells at 4°C removed both the specific lytic activity and nonspecific LT activity detectable on L-929 cells in vitro; (c) this material(s) was highly unstable, as are LT complex forms; and (d) fractionation by molecular sieving of these supernatants revealed that cell lysis was mediated by material(s) in the high (>200,000) m.w. complex form(s). The lytic effect did not appear to be due to Ab + C because supernatants that had lost their specific lytic activity could not be reconstituted with fresh sources of C. Since purified alloimmune T lymphocytes yielded more active supernatants than unseparated nonadherent spleen cells, and polyspecific goat anti-mouse Ig sera had virtually no effect on this lytic activity, the authors feel the receptor(s) in these complexes originates from the T cell(s). The data support the concept that the short-lived specific cell lytic material in these supernatants is a high m.w. complex containing αH m.w. LT subunits in functional association with specific (T cell?) antigen-binding receptor(s) molecules. These findings strongly corroborate analogous findings in the human and support the concept that the smaller m.w. LT molecules represent a system of weakly lytic but related subunits released by cells that can associate together and functionally associate with antigen-binding receptor(s) to form highly effective cell lytic complexes. Furthermore, these lytic LT-receptor complexes can be directed by the specificity of the receptor with which they are associated