PRP, administered intraperitoneally into NZB mice, twice a week, at doses 0.01-1 microgram per mouse, significantly lowered the incidence of positive Coombs' reaction and prolonged the mean age of the mice. The effect of PRP on survival of mice was better when the treatment with PRP started early (in mice showing first signs of the disease). The results suggest that PRP may induce, from a precursor pool of cells, suppressor cells controlling development of the disease. In addition, the data indicate that PRP may have a therapeutical value in treatment of autoimmune disorders, e.g. the juvenile arthritis.

Normal mice given thymocyte subpopulations preincubated with a proline-rich polypeptide (PRP) and immunized with SRBC show enhanced or suppressed humoral immune response measured by the number of plaque-forming cells (PFC). PRP induces differentiation of cells exhibiting helper or suppressive function from NAT and GAT respectively. Moreover, it was demonstrated that PRP-induced helper cells lost their activity after treatment with anti-Lyt 1,1 and the PRP-induced suppressor cells after treatment with anti-Lyt 2,1 monoclonal antibodies.

It has been shown, using thymectomized, irradiated and reconstituted mice and a proline-rich polypeptide (PRP) that glass-nonadherent thymocytes contain a precursor of helper cell, and glass-adherent thymocytes a precursor of suppressor cells in the humoral immune response to SRBC. Precursor cells differentiate into helper or suppressor cells upon in vitro contact with PRP. Moreover, it was demonstrated that NAT and GAT fractions are related to PNA+ and PNA- thymocytes respectively.