Effect of human pregnancy-specific beta1-glycoprotein on blood cell regeneration after bone marrow transplantation

Pregnancy-specific beta1-glycoprotein (PSG) is composed of a family of highly homologous proteins initially isolated from human placenta and pregnancy serum. Recent studies showed that PSGs are also present in a number of ectopic sites, including uncultured peripheral blood and bone marrow cells. This report aims at studying the in vivo effect of the PSGs on murine hematopoiesis. The profile of recovery of blood cells after transplantation of viable nucleated bone marrow cells in gamma-irradiated mice with and without the administration of the purified human protein was studied. Five groups of mice were given 0.1 microg human serum albumin, 0.1 microg IL6, 1 microg PSG, 10 microg PSG, and 50 microg PSG, respectively, per mouse per day consecutively for 20 days. The mice were bled once every 2 days, and the platelet and WBC counts were determined using a Nebauer hemacytometer (Hausser Scientific, Buffalo, NY). The recovery of platelet count after bone marrow transplant was much faster in mice receiving 1 microg PSG/day than in animals in any other group. On Day 20 post-transplant, the platelet count of animals in this group reached 178,600 +/- 15,759/microl (mean +/- standard deviation) which was significantly (P < 0.05) higher than that of any other group. On Day 26, the platelet count reached a low normal value of 190,844 +/- 6,380/microl with a range of 185,420-200,500/microl. This value was 3-fold higher than that of the control group (68,600 +/- 15,486/microl in the human serum albumin group). Mice given 1 microg or 10 microg PSG/day also had their WBC count recover significantly faster and achieved a normal value (12,440 +/- 3,680/microl for the 1-microg PSG group, and 12,154 +/- 3,016/microl for the 10-microg PSG group) within the experimental period. On the other hand, the controls, or mice given 50 microg PSG/day did not recover as rapidly and did not achieve a normal WBC count within the experimental period. These results suggest that human placental PSGs enhance platelet and WBC recovery after bone marrow transplant.