Importance of the hour of sampling in the lymphoblastic transformation assay of sheep peripheral blood lymphocytes

This paper describes the effect of the nycthemeral cycle on the lymphocyte response of sheep to different mitogens (PHA, Con A and PWM). A considerable decline in the lymphocyte response was evident in the afternoon and early in the morning in all 6 animals tested. Three peak responses were identified during a 24 hour study period, at 14.00 h, 24.00 h and 08.00 h. The results presented here suggest that this variation in lymphocyte response is a meaningful difference in the response ability of individual lymphocytes. Factors affecting the number of leukocytes and the proportion of different types of lymphocytes in peripheral blood might be the essential causes of variation. To obtain an accurate indication of an individual's immunocompetence, it is important to make a preliminary determination of the optimal hour for sampling. If this is not possible, all the samples must be taken at the same hour on each test day, in order to make significant comparisons.