Mitogen responsiveness and inhibitory activity of mesenteric lymph node cells. Conditioned medium containing T cell growth factor reverses suppressor function.

Blood-, lymph node-, and tumour-infiltrating lymphocytes (PBL, LNC, and TIL, respectively) from patients with colonic neoplasms were tested for responsiveness to phytohaemagglutinin (PHA). All populations responded, with LNC and PBL showing comparable reactivities while TIL were less reactive as assessed by incorporation of 3H-thymidine. Increased mitogen responsiveness was observed for T cells enriched by SRBC rosette formation or passage through nylon columns. Mitomycin C-treated LNC and TIL inhibited PHA induced 3H-thymidine incorporation of admixed autologous PBL, suggesting the presence of suppressor cells. Suppressor activity resided primarily in the SRBC rosetting population and was dose-dependent, with increasing numbers of LNC giving greater diminution of PHA response. Suppression by LNC was apparent only when they were added to PBL responders within 6 h of the initiation of stimulation assays, in common with the effects of Concanavalin A (Con A)-induced suppressors on PBL phytomitogen responsiveness. Con A-induced and LNC-suppressor activity could be reversed by addition of lymphocyte-conditioned medium (CM) containing T cell growth factor (TCGF; interleukin IL-2). These data provide further evidence that the suppressor phenomena observed in this system are a function of activated T cells present both in drainage lymph nodes and at the tumour site.