New insight into lymphocytic chalone research. The 'facteur thymique Sérique' might be responsible for part of the immunosuppressive activity detected in the 'chalone fraction'.

Immunosuppressive activities have been detected in bovine spleen extracts and attributed to the presence of a 'lymphocytic chalone'. Following the immunosuppression of a T cell-dependent humoral response in mice as assay, we purified a peptide to homogeneity present at a concentration of 10-50 ng/kg of spleen whose properties were identical to those of the serum thymic factor. This factor appeared to be a regulator of the humoral immune response in the splenic extract and as such might be responsible for part of the immunosuppressive activities detected in the splenic 'chalone' fraction.