A comparison of the in vitro and in vivo activities of conjugates of anti-mouse lymphocyte globulin and abrin.

Anti-mouse lymphocyte globulin and normal immunoglobulin have been conjugated to abrin using two procedures, one involving linkage through an amide bond and a piperazine ring and the other the introduction of two amide bonds flanking a disulphide bridge. The four conjugates produced were equipotent as inhibitors of protein synthesis in rabbit reticulocyte lysates. Each antibody-containing conjugate was a more effective inhibitor of protein synthesis in cultured cells than the equivalent normal immunoglobulin-containing conjugate. In addition the conjugates with disulphide linkage groups were ten times more potent than their counterparts. The disulphide conjugates were also twice as toxic to mice in an acute toxicity test but when used to suppress their immune responses to sheep red blood cells it was the non-disulphide-linked conjugates that were superior. In all instances antibody-containing conjugates were more powerful immunosuppressants than those containing normal IgG. The results are taken to indicate a relative lack of stability of the disulphide conjugates in the tissues.