Specific suppression of antibody responses in vivo. I. Effects of in vitro produced suppressor factor.

KLH-specific suppressor factors produced in vitro efficiently diminished primary and secondary responses to trinitrophenyl keyhole limpet haemocyanin (TNP-KLH) in vivo. Both IgM and IgG responses were approximately equally affected, These suppressor factors were not genetically restricted, as allogeneic suppressor factors worked as efficiently as syngeneic factors. Furthermore, xenogeneic human suppressor factors were effective in mice and suppressed the responses as efficiently as syngeneic factors. The kinetics of the response in suppressed and non-suppressed mice was the same, indicating that the magnitude of the response was affected and not merely its time course. Prior injection with suppressor factor did not cause suppression of response, while suppressor factor injected at the same time as or soon after the antigen did, suggesting that it might act at the effector stage. The mechanism of action of this unrestricted suppressor factor, and the use of mouse model for in vivo testing of human suppressor factors is discussed.