Dose-response curves for lymphoblast transformation by phytohemagglutinin stimulation.

In order to seriously evaluate the lymphoblast response to PHA, we studied the effects of different doses of the mitogen and different culture periods in the normal population. According to our results, we classified the subjects into 2 groups, high responders and low responders. No significant differences were found among the groups in the spontaneous blast transformations. Maximum levels of stimulation were obtained with PHA doses of 2 to 10 micrograms/10(5) cells/100 microliters. Maximal response in the high responder group was observed on the fifth day of incubation, whereas for low responders, maximum stimulation was observed on the third day of incubation. Two populations responding with different intensity to PHA were identified, suggesting that the different responses were conditioned by genetic factors. The interpretation of the lymphoblast response to phytohemagglutinin is a much more complex task than is currently believed. The variations in response may result from alterations in the immune system as well as from the peculiar genetic characteristics of each individual.