The relationship between eosinophilic leukocytes and phospholipase B activity in some rat tissues

Spleen, peritoneal fluid, uterus and bone marrow of the rat have been studied for their content in phospholipase B (E.C. 3.1.1.5) and the presence of eosinophilic leukocytes. A close correlation has been found between cell counts performed on fixed and stained histological sections or cell suspensions and enzymatic activity of the same preparations. Equivalent values of phospholipase B activity per unit cell are found in spleen, uterus and peritoneal fluid. A lower average value is indicated for the bone marrow eosinophils. A tentative explanation for this discrepancy is offered on the basis of histochemical evidence showing that a fraction of the eosinophilic cells do not stain for phospholipase B activity. The number of these cells is approximately equal to that of the precursor immature cells of the eosinophilic leukocyte system. The evidence indicates that in normal conditions a major portion, if not all, of the phospholipase B activity of the organs studied is contributed by the eosinophilic leukocytes present in the tissue.