Effect of removal of ovine squamous cell carcinoma on peripheral lymphocyte stimulation by tumour extracts and phytohaemagglutinin.

Mock-operation of normal tumour-free sheep was not associated with significant changes in blastogenic responses of peripheral lymphocytes (BRPL) to phytohaemagglutinin (PHA-P) or tumour extracts (TA). In age-matched tumour-bearing sheep, tumour removal was associated with a significant prolonged increase in BRPL to PHA-P and TA about three weeks after operation. This increase was significantly greater in sheep with mature than with early tumours. No increase in BRPL occurred in sheep with secondary lesions. Challenge of tumour-removed sheep with TA 15 weeks after operation was associated with a significant anamnestic-type short-term surge in BRPL to PHA-P and TA, which was significantly greater in sheep which had previously borne advanced tumours. Mock-operated normal mature sheep challenged with TA also showed a lowgrade anamnestic-type response of BRPL to PHA-P and TA. The results are discussed in terms of the mechanisms of BRPL suppression, and of specific reactions in normal sheep.