RELATIONSHIP BETWEEN EOSINOPHILIA AND RESPONSIVENESS TO INFECTION WITH TRICHOSTRONGYLUS-COLUBRIFORMIS IN SHEEP

Lambs with genetically determined increased immunological responsivene ss to Trichostrongylus colubriformis (high responders) had more eosino phils in cutaneous reactions to the mitogen phytohaemagglutinin (PHA) both before and during infection compared with those bred for suscepti bility (low responders). In contrast, eosinophil numbers in both blood and cutaneous reactions elicited by third-stage T. colubriformis larv al antigen were similar in high and low responders before infection. F ollowing vaccination and challenge, high responders had elevated eosin ophil numbers in blood and antigen-stimulated skin. In unselected shee p, although eosinophil numbers in cutaneous reactions to PHA were rela ted to responsiveness to a challenge infection with T. colubriformis, there was a closer relationship between blood eosinophil numbers and r esponsiveness. Infection with T. colubriformis increased eosinophil nu mbers in cutaneous reactions to PHA and appeared to augment the differ ence between eosinophil counts in high and low responder sheep. Measur ement of the ability to produce eosinophil activating factors, or for eosinophils to respond to such factors might therefore be useful in id entifying individual sheep with increased responsiveness to T. colubri formis infection.