Two patterns of NK activity changes following blood donation: decrease in the beginners and restoration in regular blood bank donors.

NK cell activity of peripheral blood lymphocytes was determined in voluntary blood bank donors in a standard 4-hr 51Cr-release cytotoxicity assay. When blood donors were divided into groups according to the total amount of blood they had donated in the past, decreased NK activity was found in "moderate" donors who had donated between 3 and 9 l of blood, but not in those who had donated < or = 3 or more than 9 l of blood before testing. This observation was the rationale for a study on the effects of regular blood donations on NK activity in randomly selected voluntary blood bank donors re-tested over a period of time. The study demonstrated decreased NK activity in the second measurement in donors who had donated up to 6 l of blood before the study, and an increase in NK activity between the first and the second testing in those who had donated more than 6 l of blood. This result, together with data obtained at the population level, suggests that some compensatory mechanism(s) regulate NK activity in the course of regular blood donation.