[Leukocytes, between morphology and function].

Knowledge regarding the immune activity of lymphocytes is quite recent. Polymorphonuclear phagocytosis was described about a century ago, but subdivision of lymphocytes into T and B cells dates back only two decades. Pathophysiologic observations on lymphocytes in the course of infectious mononucleosis have been a source of extremely interesting data. Recognizing different T lymphocyte subsets has enormously enriched knowledge of their functional activities, while the contribution of morphological studies has been very limited.