The immunoregulatory granulocyte factor (GF). III. Characteristics of target cells for GF

Granulocyte factor (GF) is a substance secreted selectively from the specific granules of granulocytes in the first minutes of adherence or phagocytosis. GF possesses many immunoregulatory functions. We applied flow cytometric analysis to evaluate the target cells responsible for GF action. Resting lymphocytes did not display binding sites for GF, but 93 +/- 4.6% of the neutrophils isolated from peripheral blood bound GF (mean fluorescence = 122 +/- 11). GF was bound by 26 +/- 7.6% of the lymphocytes from nonstimulated and 42.6 +/- 12% of the lymphocytes from PHA-stimulated cultures, and the mean fluorescence intensity was 14.5 +/- 1 and 54 +/- 10.6, respectively. PHA-stimulated CD8+ cells presented higher expression of binding sites for GF than CD4+ cells. Binding sites for GF were found on 66 +/- 5.1% of activated cells expressing the receptor molecule to IL-2 (CD25) and 50.3 +/- 7.4% of cultured lymphocytes expressing the early activation marker CD69. These values were significantly higher in comparison to the percentage of CD25- and CD69- cells that bound FITC-labeled GF (10.3 +/- 3.3% and 11.3 +/- 3.5%, respectively). The binding was specific, and preincubation of the cells with GF almost completely abolished FITC-labeled GF binding. It has also been shown that GF binds to lymphocytes via molecules other than CD16. High-performance liquid chromatography (HPLC) with fractionated GF showed three separate fractions and two of them had GF-like activity, as demonstrated in the mixed lymphocyte reaction (MLR).