Immunosuppressive ALS. II. Antibody to Ia antigens in heterologous anti-lymphocyte serum.

The relationship between Ia alloantigens and xenoantigens detected by immunosuppressive heterologous anti-lymphocyte sera has been investigated. Three rabbit anti-rat lymphocyte sera were examined for the presence of antibodies to Ia antigens. Two of these sera, an anti-thymus membrane and anti-lymphocyte sera detected labelled cell-surface Ia antigens (mol. wt 35,000 and 27,000) present on rat spleen B cells. The third antiserum, prepared against fractionated soluble lymphocyte antigens, was essentially non-reactive with these antigens. Of these three heterologous antisera, the anti-membrane serum reacted with the same antigens detected by two alloantisera. It seemed possible that such an antiserum could modify a recipient animal's immune response in vivo in a fashion identical to alloantibody to Ia antigens. In fact, all three heterologous antisera, including one devoid of antibody to Ia proved immunosuppressive in vivo. These results suggest that antibodies to antigens other than Ia can induce prolonged allograft survival. Since heterologous sera bind Ia antigens, it remains to be determined whether monospecific heterologous antisera to Ia antigens can allograft survival. The results raise the prospect that more than one antibody specificity may contribute to the immunosuppression achieved with ALS.