Characterization of thymosin-responsive peripheral blood null cells.

Suspensions of human peripheral blood lymphocytes were enriched for E rosette-negative (E-) surface immunoglobulin-negative (SIg-) "null" cells expressing either human T or human B lymphocyte antigens. These enriched suspensions were then tested for responsiveness to activation of E rosette formation by thymosin. Thymosin activated some human T lymphocyte antigen-positive E-SIg- but not human B lymphocyte antigen-positive E-SIg- cells to form E rosettes. Therefore, thymosin-responsive peripheral blood null cells appear to be precommitted to the T- cell line of differentiation.