Suppressor factor produced by neonatal mouse spleen cells

Spleen cells from 5- to 6-day- old BDF₁ mice produce a soluble suppressor factor (SF) when cultured for 2–4 days in the presence of 10% fetal calf serum. This suppressor factor inhibits the mixed lymphocyte reactivity of adult mouse spleen cells as well as the in vitro generation of cytotoxic cells. The SF which is not H₂-restricted or antigen specific is most effective when added in the early phase of the culture period. The SF is resistant to heat and uv treatment and appears to consist of a large and small component. It is resistant to treatment with pronase or trypsin. The SF appears to be produced by neonatal spleen cells which are not adherent to plastic or Sephadex G-10 and are insensitive to treatment with anti-Thy 1.2 and complement. Incubation of SF with peritoneal exudate cells reduces suppressor activity.