EN
Since the discovery indicating that thymus derived lymphocytes (T cells) can be divided into two subpopulations: CD8+ (killer) and CD4+ (helper) cells, subsequent studies revealed bewildering heterogeneity of T cells. In the present review an attempt is made to present the actual picture of T cell heterogeneity, introduce some order into nomenclature and summarize the rules behind the development and selection of different, currently recognized T cell subsets.