Lymphocyte response to phytohemagglutinin: temporal variation in normal dogs

The lymphocyte response to mitogens is frequently used as a screening method for monitoring general immunocompetence. In practice, however, the technique is potentially misleading. The results presented here suggest that temporal variation in lymphocyte response is the norm. Considerable variation in response to phytohemagglutinin was found for several dogs tested over different time periods. The response for any individual dog also fluctuated whether testing was at 2-week intervals, daily, or even every 4 h. This temporal variation remained whether separated lymphocytes or whole blood was cultured and when the results were expressed on a per lymphocyte basis. This suggests that there is a real difference in the response capability of individual lymphocytes. Factors affecting the numbers of leukocytes and the proportions of different types of lymphocytes in the peripheral blood are suggested as a possible source of the variation. Because of the inherent variation in lymphocyte responsiveness, it is necessary to test at different intervals to obtain an accurate indication of the general status of an individual's immunocompetence and to determine the time of peak response capability for that individual.