In vitro responses of lymphocytes from cattle with advanced Mycobacterium paratuberculosis infection to homologous and heterologous antigens.

The accuracy with which the purified lymphocyte and whole blood modifications of the lymphocyte stimulation test were able to detect animals with clinical Johne's disease was compared with that of the complement fixation test and microscopic faecal examination. Confirmatory diagnosis of Johne's disease was based upon histopathological examination of intestinal tissue. False positive results were obtained only with the complement fixation test. The only test not giving rise to false negative results was the purified lymphocyte modification of the lymphocyte stimulation test using johnin at 20 micrograms/ml and avian tuberculin at 20 micrograms/ml or 2 micrograms/ml. The whole blood technique was less accurate than the purified lymphocyte technique for the in vitro detection of cell-mediated immune responses to antigens. The purified lymphocyte technique appears to have potential as an diagnostic test for Johne's disease in cattle and merits further evaluation.