Proline-rich polypeptide (PRP) from ovine colostrum. Bi-directional modulation of binding of peanut agglutinin, resistance to hydrocortisone, and helper activity in murine thymocytes.

A proline-rich polypeptide (PRP) isolated from ovine colostrum has a regulatory effect on the immune response. The present report demonstrates that the polypeptide can cause bi-directional modulation of surface markers and function of murine thymocytes. PRP is able to reduce binding of peanut agglutinin (PNA) to murine PNA+ thymocytes and to increase the binding of PNA to PNA- cells. This transition of binding ability can be reversed by a second treatment of cells with PRP. PRP is also able to transform cortisone-resistant thymocytes into cortisone-sensitive, and vice versa. Helper cells induced by PRP from murine glass-nonadherent thymocytes (PNA+) showed suppressor activity after the second treatment with PRP. The observed changes were occurring concomitantly, i.e. changes in binding of PNA were accompanied by changes in resistance to cortisone and in expression of helper or suppressor activity. Bi-directional effects of PRP on PNA-binding ability, sensitivity to hydrocortisone, and helper-suppressor function, makes this polypeptide unique among immuno-modulators known.