Primary and secondary wattle swelling response to phytohemagglutinin as a measure of immunocompetence in chickens.

Wattle responses of 2-to-8-week-old chickens to phytohemagglutinins PHA-P and PHA-M were studied. Dilutions of PHA-M that did not induce wattle swelling after one injection did cause readily detectable swelling when injected a second time 1 week later. These responses were absent in birds subjected to thymectomy and gamma-irradiation at hatching and in birds treated with cyclosporin A during the week of sensitization, indicating that these responses are T-cell-dependent. Chickens bearing transplantable fibrosarcomas failed to show responses. It is suggested that reactivity to a second injection of PHA-M may be used as a measure of immunocompetence at the T-cell level in very young chickens.