Thymosin Induces Helper Function in OKT3‐Positive, E‐Rosette‐Negative Human Cord Blood T Cells

Abstract

E-rosette-negative lymphocytes (T_E-), which express monoclonal T-cell markers (OKT3⁺) were found in higher frequencies in humnn cord blood (CB) (30% by phenotype and 11.7% by sequential rosette isolation) than in adult peripheral blood lymphocytes (13% by phenotype and 3.7% by isolation). T_E- cells had very low levels of 5′-nucleotidase. a lymphocyte maturational marker low in thymocytes. Like other CB T cells. T_E- cells possessed marked suppressor capability. Irradiated T_E- cells from two cord blood samples demonstrated helper activity tor Ig production hy adult B cells. In six cord blood samples, however, irradiated T_E- cells lacked helper activity. When incubated with thymosin, these T_E- cells became E^- and differentiated into inducer-helper T cells. These observations confirm previous assumptions that CB T cells are not fully differentiated. Furthermore. T cells from different CB samples may be at various stages of ontogeny. We have also shown that thymosin fraction 5 is able to confer a new immunoregulatory function.