Non-specific inhibitor made by T acceptor cells inhibits both the afferent and efferent stage of the contact sensitivity reaction.

In the T suppressor circuit which affects contact sensitivity, the T acceptor cell (Tacc) armed with T suppressor factor (TsF) and then triggered by antigen and major histocompatibility complex products (I-J) releases non-specific inhibitor (nsINH). These non-specific inhibitor(s) affect both the efferent and afferent stage of the contact sensitivity reaction and were originally detected by the inhibition of the passive transfer of contact sensitivity. The nsINH also blocks the induction of contact sensitivity when given intravenously at the time of immunization but has no effect when given at the time of challenge. Similarly, it blocks proliferation in the regional lymph nodes induced by contact sensitizer in a dose-dependent fashion; it acts when given at the time of immunization but not 1 day later. This effect is antigen non-specific and H-2 unrestricted. The nsINH bears I-J determinants as shown by affinity chromatography on monoclonal antibody. The nsINH comes from the Tacc and is not a breakdown product of the TsF. This is shown by the fact that, when the Tacc and TsF have I-J of different genotypes, the genotype of the nsINH corresponds to that of the Tacc. Parallel measurements of inhibition of lymphoproliferation and of passive transfer show that the nsINH has a molecular weight of 50-60 Kd and a pI around 6.8 and suggest that similar or identical molecules block both the afferent and efferent stage of the contact sensitivity reaction.