Composition of a Suppressor Factor That Inhibits the Immune Response to Lactate Dehydrogenase B

Hybridomas obtained by fusion of lactute dehydrogenase B (LDH_B)‐aciivatcd suppressor T (Ts) cells with the BW5147 thymoma produce a suppressor factor (TsF) that inhibits the proliferation of LDH_B‐activated helper T (Th) cells. A similar factor (TsE) is contained in the extract of suppressor hybridomas. Both TsF and TsE are specifically retained by LDH_B‐immunoadsorbent columns. Both consist of two components, an antigen‐binding component (ABC) and possibly a major histocompatibility complex (MHC) component. The latter reacts with certain monoclonal antibodies specific for MHC determinants. The two components arc covalently associated in the IsF and noncovalcntly associated in TsE. Mixing of the two components reconstitutes the activity of the TsF or TsE. Disruption of the ABC's tertiary structure results in its inability to reconstitute suppressive activity on mixing with the MHC components. The ABC may contain an intrachain disulphide hond(s). Suppression is obtained when Th cells are incubated first with the ABC and then with the MHC component or vice versa, provided that the incubation period is at least 4 h. The MHC component is also produced by nonsuppressor hybridomas but not by mitogen‐stimulated blasts or by the parental thymoma. The TsF is a glyeoprotein with a molecular weight ot about 120.000 to 160.000. The molecular weight of the ABC is about 76,000–86,000 and of the MHC component about 30,000–37,000.