Suppression of blastogenic response of peripheral lymphocytes by serum from ovine squamous cell carcinoma bearing sheep.

Sera from sheep with ovine squamous cell carcinoma are shown to contain a factor which nonspecifically inhibits blastogenesis of T lymphocytes. This blastogenic inhibitor is stable at 56 degrees C for 30 min, passes a 430 nm filter, and increases in concentration (or efficiency) with increasing tumour volume. Tumour removal is associated with effective circulatory disappearance of the inhibitor and coincides with recovery of cell-mediated responses within five weeks. The inhibitor adsorbs readily to leucocyte populations from normal and tumour removed sheep. It is suggested that the blastogenic inhibitor is mediated by the tumour to cause immunosuppression through an undetermined B lymphocyte suppressor pathway, and acts as a mechanism protecting the tumour from immune rejection by T lymphocytes.