PAF AND HEMATOPOIESIS .3. PRESENCE AND METABOLISM OF PLATELET-ACTIVATING-FACTOR IN HUMAN BONE-MARROW

Platelet-activating factor (PAF) is a phospholipid compound with major immunoregulatory activities. The present study shows that human bone marrow contains 576 +/- 39 pg PAF/ml (n = 35). Bone marrow-derived PAF exhibits the same biophysical and biological properties that syntheti c PAF. PAF concentrations in bone marrow are correlated with the granu locyte (r = 0.4, P = 0.02) but not with the lymphocyte (r = 0.24, P = 0.17) and the monocyte(r = 0.12, P = 0.48) counts. In bone marrow PAF is inactivated by a plasma PAF acetylhydrolase activity (48.0 +/- 2.3 nmol/min per mi, n = 34). Experiments with [H-3]PAF indicate that huma n bone marrow cells actively metabolize this potent molecule by the de acetylation-transacylation pathway. Results of this investigation indi cate the permanent presence of significant amounts of PAF in bone marr ow suggesting its putative involvement in the processes of bone marrow cell proliferation and maturation.