The role of blocking antibodies in immunological enhancement.

Hyperimmune mouse serum and its fractions were tested in vivo for enhancement of mouse tumour growth and in vitro for blocking of cell-mediated cytotoxicity of cultured target cells. Whole serum, 7S, γG1 and γG2 were active in prolonging the survival of three CBA tumours in A.SW hosts and also in blocking target cell destruction by sensitized lymphoid cells. Thus an efferent blockade or protection of target tumour cells from immune cells from immune cells by antibodies plays a significant role in this phenomenon. However, an earlier block in the immune response was also detected, for lymph node and spleen cells from mice given both antiserum and tumour cells showed weaker immunity than lymphoid cells from mice injected with tumour alone. Whether this early block was afferent or central could not be determined from the experiment. Thus two blocks demonstrable by microassay for cell-mediated immunity are at least partially responsible for enhancement of tumour growth.