Abstract
Monoclonal anti‐Lyt‐1.1 alloantibody was produced as tissue culture supernatant and administered to mice. The antibody, given intraperitoneally, resulted in the suppression of all T cell functions studied, but was without direct effect on B cells. Thus, skin and tumor allograft survival was prolonged and there was suppression of the delayed‐type hypersensitivity response; T cell help in the anti‐sheep red blood cell antibody response, responder cells in the mixed lymphocyte reaction (MLR), leucoagglutinin‐responsive cells, cytotoxic T cell (T~c~) function and the induction of T~c~ were either totally or partially suppressed, all these responses being mediated by Lyt‐1^+^2^−^ or Lyt‐1^+^2^+^ cells in CBA/H mice. By contrast, there was no inhibitory effect on the MLR‐stimulating or lipopolysaccharide‐responsive cells. The administration of the anti‐Lyt‐1.1 antibody was accompanied by a depletion of Lyt‐1.1^+^ T cells from both spleen and lymph node. These studies indicate that the monoclonal anti‐Lyt‐1.1 antibody is active in vivo with a selective effect on T cells. The results also have important implications for studies of T cell interactions in the mouse in vivo, and for similar studies in man.