In vitro correlates of rejection. I. Suppressive effect and specificity in mixed lymphocyte interaction of alloantiserum producing hyperacute rejection.

A hyperimmune antiserum from WfBN F1 hybrid rats primed to hyperacutely reject LBN F1 cardiac allografts has been studied. A large volume of antiserum will cause allograft rejection in less than 1 day. In the in vitro MLI, concentrations of this antiserum as low as 0.05% are markedly suppressive. This suppression is dose-dependent and immunizing-strain-specific at concentrations less than 1%. The suppressive activity is in the globulin fraction. After in vivo absorption, donor-strain specificity is clearly shown, with some cross-reactivity with third-party ACI strain. Moderate suppression of the rat MLI was seen with some normal rat sera, and augmentation of the MLI was seen in some experiments when very dilute concentrations of hyperimmune serum were used. Since suppression or augmentation of the MLI can occur as a function of antiserum dose and presumably antibody concentration, single measurements of MLI blocking factors may be misleading, and MLI suppression is not necessarily a correlate of allograft enhancement.