Distinct properties of Thy‐1 antibodies elicited in rats by immunization with mouse brain

Rats are known to possess antigenic determinants related to the Thy‐1.1 allele. Immunization of rats with brain homogenates from mice carrying either the Thy‐1.1 or the Thy‐1.2 alleles resulted in the production of antisera which were cytotoxic for thymus cells of both strains of mice. Lymph node, spleen and cortisone‐resistant thymus cells were refractory to the cytotoxic effect of rat anti‐mouse brain sera. Peripheral lymphocytes were fully capable of absorbing the cytotoxic activity of the sera on thymus cells, although the concentration of the antigen on their cell surface was considerably less than on thymus cells. Blocking experiments with alio‐ and xenoantisera to Thy‐1 antigens suggested that the antigen detected by rat anti‐mouse brain sera is related to the Thy‐1 system. The Thy‐1 specificity detected by rat antisera seems to differ from previously described Thy‐1 antigens in that it attains a high concentration on thymus cells but is relatively deficient in its expression on peripheral T cells.