Two types of mouse helper T-cell clone Implications for immune regulation.

Lymphocytes mediate many important functions of the immune system, such as antibody production, cytotoxicity, and immediate and delayed type hypersensitivity (DTH). In 1968, two major divisions of lymphocytes were recognized: B cells (derived from bone marrow) that produce antibody, and T cells (thymus-dependent) responsible for DTH, cytotoxicity, and regulation of many B- and T-cell functions. The discovery of subset-specific cell surface antigens subsequently allowed division of T cells into two classes: mainly responsible for helper and DTH functions, T cells bearing Lyt-1 and L3T4 antigens, and T cells bearing the Lyt-2 antigen responsible for the majority of cytotoxic and suppressor functions. Evidence from studies with normal cell populations and T-cell clones has since suggested that the Lyt-1(+)L3T4(+)Lyt-2(-) helper T cell population can be divided into at least two types. In this article, Tim Mosmann and Robert Coffman review evidence for this subdivision obtained with T-cell clones grown in vitro and discuss the implications of differences in function and lymphokine synthesis between the two types of cloned helper T cell.