Specific in vitro lymphocyte response of chickens injected with killed Mycobacterium tuberculosis.

An in vitro microassay for lymphocyte transformation, using 3H-thymidine incorporated into avian peripheral blood leukocytes, is described. The transformation responses of 1 X 10(6) leukocytes stimulated by the nonspecific mitogen, phytohemagglutinin-M (PHA-M), were equivalent with 68- and 92-hour incubation durations. The PHA-M in concentration of 50 micronl/ml produced greater stimulation than did that of 25 or 100 micronl/ml. The transformation response to PHA-M was significantly affected by the lot of bovine fetal serum used to supplement the RPMI 1640 culture medium. The specific antigen, purified protein derivative (PPD) of tuberculin, stimulated significant transformation in cultures of 1 X 10(6) leukocytes from Mycobacterium tuberculosis-sensitized fowl. The PPD at concentration of 50 microng/ml was superior to 100 or 150 microng/ml, and 68-hour incubation was significantly better than 92-hour incubation. The magnitude of the in vitro transformation response to PPD was greater at 6 weeks after sensitization than at 2 or 4 weeks, and it was not directly related to the magnitude of the in vivo wattle test response in sensitized chickens.