Prothymosin alpha receptors on lymphocytes.

Recent results indicate that prothymosin alpha (ProT alpha) may be useful in designing future therapeutic interventions in cancer patients and in potentiating the immune system. We described recently the presence and characteristics of two binding sites for ProT alpha on human peripheral blood mononuclear cells (PBMC). In search of a receptor upregulation, we decided to corroborate this finding on two lymphocytic populations, (PHA-activated) lymphoblasts and YT cells. The kinetics of [125I]ProT alpha binding to lymphoblasts were fast at room temperature but with YT cells were slower. Analysis of steady-state binding data identified two binding sites in lymphoblasts with an apparent equilibrium Kd of 44-75 pM and 4228-9143 sites per cell for the high-affinity receptor and 1.7-2.9 nM and 20,534-35,044 sites per cell for the low-affinity receptor. However, it identified only one site with a Kd of 265-435 pM and 8318-27,237 sites per cell in YT cells. We conclude that exists a ProT alpha receptor in the CD3+ T cell population, and this presence is regulated. After binding to cell surface, [125I]ProT alpha is internalized in a short period of time and then degraded; therefore, we conclude that the dynamics of ProT alpha receptor turnover in part determines the concentration of ProT alpha available to induce its enhancing effects.