The Detection of Tuberculin-sensitive Lymphocytes from Bovine Blood by Uptake of Radio-labelled Nucleosides

Abstract

Summary These investigations form part of a programme to study methods other than the intradermal test for the diagnosis of bovine tuberculosis. The in vitro uptake of cither 3H thymidine or 3H uridine was measured to study the tuberculin sensitivity of lymphocytes from cattle sensitized by a single dose of 50 mg BCG injected subcutaneously from 80 to 443 days previously. The dose-response curves in vitro of specifically sensitized bovine lymphocytes and tuberculin PPD, and the relationship of the age of the cattle to the sensitivity of the test were measured. Further information was gained on the effect of intercurrent tuberculin skin tests on the in vitro tests, and the effect of such skin tests on levels of circulating anti-mycobactcrial antibody. 1. Between 5μg and 100μg of tuberculin PPD per ml of culture medium were needed for significant stimulation of bovine lymphocytes. 2. Initially, tuberculin-stimulated lymphocytes from 23-month-old cattle incorporated significant amounts of 3H thymidine but those from 11-month-old cattle did not. However, repeated blood sampling of the 11-month-old cattle was followed by the appearance of tuberculin-sensitive blood lymphocytes which incorporated 3H thymidine. 3. The reactivity of circulating lymphocytes was temporarily depressed 3 days after the intradermal injection of 10,000 T. U. of tuberculin PPD, but lymphocyte reactivity had returned to previous levels by 7 days. 4. Serum antibody to mycobacterial polysaccharide was depressed 7 days after the skin test and in subsequent blood samples. 5. There was a significant correlation between the increase in skin thickness at 48 h and the reactivity of circulating lymphocytes tested in vitro on the day of the skin test. 6. The difference in 3H uridine incorporation by tuberculin-stimulated and control cultures was first found to be significant at 44 h, compared with 52 h for 3H thymidine.