Alkaline phosphate in the differentiation of guinea pig T lymphocytes.

The majority of the guinea pig thymocytes have an intensive alkaline phosphatase (AP) activity, whereas less than one per cent of the peripheral lymphocytes are AP positive. The number of peripheral AP positive lymphocytes decreased after thymectomy and after antithymocyte serum treatment, and some of them formed. E-rosettes with rabbit red blood cells. The observations support the idea that some of these AP positive peripheral lymphocytes are T cells. It seems evident that the AP positive cortical (immature) thymocytes contain two separate cell lines; during the maturation one differentiates into AP negative and the other remains AP positive. This differentiation seems to occur within the thymus.