Responses of bovine lymphocytes to heat shock as modified by breed and antioxidant status

Abstract

We tested whether resistance of lymphocytes to heat stress is modified by breed, intracellular glutathione content, and extracellular antioxidants. In the first experiment, lymphocytes from Angus (Bos taurus, non-heat-tolerant), Brahman (B. indicus, heat-tolerant), and Senepol (B. taurus, heat-tolerant) heifers (12 heifers per breed) were cultured at 45°C for 3 h to evaluate thermal killing, at 42°C for 12 h in a 60-h phytohemagglutinininduced proliferation test, and at 42°C for 1 h to measure induction of heat shock protein 70 (HSP70). Killing at 45°C was affected by breed × temperature (P < .01); the decrease in viability caused by a temperature of 45°C was greater for Angus than for Brahman or Senepol. For phytohemagglutinin-stimulated lymphocytes, heating to 42°C reduced [³H]thymidine incorporation equally for all breeds. Viability at the end of culture was affected (P < .001) by a breed × temperature interaction because the decrease in viability caused by culture at 42°C was greatest for lymphocytes from Angus heifers. Heat shock for 1 h at 42°C caused a two- to threefold increase in intracellular concentrations of HSP70, but there was no interaction of temperature with breed. In another experiment (with lymphocytes harvested from three Holstein cows), buthionine sulfoximine, a glutathione synthesis inhibitor, inhibited (P < .01) proliferation of phytohemagglutinin-stimulated lymphocytes at 38.5 and 42°C. Addition of the antioxidants glutathione or thioredoxin to culture did not reduce the effects of heating to 42°C on proliferation.(ABSTRACT TRUNCATED AT 250 WORDS)