Prolongation of skin allograft survival in mice after pretreatment with an extract of human platelets in combination with donor antigen.

Intraperitoneal injection of human platelets or of an extract released from these cells in mice results in significant prolongation of skin allograft differing in H-2 locus. We differentiated between a primary phase (optimum after about 20 h) and a secondary phase (optimum after 2-3 months). The extract was injected twice together with spleen cells as donor antigen, twelve weeks later skin grafting was done. The average transplant survival was 21.4 days in contrast to 11.4 days in the zero-control. The repeated graft of second set reaction also had a prolonged survival. A sensibilization in the second set was not observed. The xenogeneic origin of the platelets used was against the assumption of the participation of original superficial antigens from platelets in the described immune modulation process.