CTL Helper Factor(s) Produced by Peritoneal Cells of Mice Immunized to Listeria monocytogenes : Relationship to Interferon*

Abstract

We have studied the relationship of interferons (IFN) to soluble helper factor(s) produced in vitro by activated peritoneal exudate cells of mice immunized to Listeria monocytogenes. This helper factor(s) can assist the generation of cytotoxic lymphocytes (CTLs) in response to allogeneic thymocytes that have been heat-treated to remove functional antigens that would normally stimulate CTLs in the absence of added exogenous help. In addition to IFN and CTL helper activity, a thymocyte proliferative activity also was detected. There appeared to be collaboration between activated nonadherent T cells and macrophages (MØ) in the production of all three activities. The IFN produced appeared to be primarily IFN-γ; however, some IFN-α/β probably was present as well. Although CTL helper activity and IFN were both contained in fractions comprising the major peak of thymocyte proliferative activity when supernatant fluids containing all three were chromatographed, functional IFN could be deleted with pH-2 and anti-IFN treatment without appreciably altering the other two activities. Furthermore, when fluids containing helper activity, but depleted of functional IFN, were added to cultures of responder lymphocytes and heat-treated thymocytes, IFN was produced during the course of the five day culture as were CTLs. In parallel cultures to which fluids containing helper factor(s) were not added, no IFN was produced, and no CTLs were generated. Thus, although fluids having activities required for the generation of CTLs may be depleted of IFN at the time they are added to cultures, a role for IFN in some phase of CTL development cannot be excluded.