Production of granulocyte-macrophage colony-stimulating factor but not IL-3 by normal and neoplastic human B lymphocytes

The ability of human B cells to produce granulocyte-macrophage (GM)-CSF and IL-3 was investigated. B cells, isolated from tonsils or from the peripheral blood of patients with B cell chronic lymphocytic leukemia using mAb and immune rosettes, were cultured with or without Staphylococcus aureus Cowan strain I. GM-CSF and IL-3 were measured in the culture supernatants using a bioassay based on the selective proliferative response of the MO7e megakaryoblastic cell line to IL-3 or GM-CSF. S. aureus Cowan I-stimulated normal B cells released measurable amounts of GM-CSF but not of IL-3 as determined in neutralization assays with specific mAb in the MO7e cell line test. Some of the unstimulated normal B suspensions also produced GM-CSF, albeit in lower quantities. When normal B cells were fractionated into small (resting) and large (activated) B cells by Percoll density gradients, spontaneous GM-CSF production was detected only in the large cell fractions, but small cells were induced to produce GM-CSF upon S. aureus Cowan I stimulation. On a per cell basis, tonsillar B cells were found capable of releasing more GM-CSF than activated peripheral blood monocytes. The amount of GM-CSF produced by B cells was always inferior to that released by stimulated peripheral blood T cells or NK cells. The purified B cell suspensions from all 14 B cell chronic lymphocytic leukemia patients studied released GM-CSF but not IL-3 in the culture supernatants, sometimes even in the absence of stimuli. Northern blot analysis on total or poly(A)+ RNA confirmed the presence of GM-CSF, but not of IL-3, mRNA transcripts in both normal and malignant B cells. The results of these studies support the notion that activated human B lymphocytes release sufficient GM-CSF to play a role in the control of both hematopoiesis and the inflammatory process.