Abrogation of cell‐mediated immunity by hyperimmune alloantiserum: Mechanisms and correlation with allograft enhancement

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Abstract
Alloantiserum blocking of cell‐mediated immunity as measured by a 51chromium release cell‐mediated cytotoxicity assay has been characterized and correlated with immunological enhancement of tumor allografts across H‐2 barriers in mice. Alloantiserum blocking was found to be immunologically specific, quantitative, and highly reproducible. Cytotoxicity could be blocked by adding alloantiserum directly into the reaction mixture or by pretreating the target cells with alloantiserum. Effector cells could also be specifically blocked by pretreatment with alloantigens or with a fraction isolated from a mixture of alloantiserum and ascitic fluid containing alloantibody. Pretreatment of effector cells with alloantibody alone had no blocking effect. Upon purification, this fraction dissociated into IgG and a small molecular species with some biochemical and antigenic properties analogous to H‐2 fragments. These observations are consistent with the hypothesis that the isolated fraction may have been an antigen‐antibody complex consisting of alloantibody and H‐2 alloantigen. In addition, blocking was shown to be surmountable under certain conditions by increasing the number of effector cells. The implications and mechanism of alloantiserum blocking and its relationship to immunological enhancement are discussed.