Effect of recombinant human granulocyte colony-stimulating factor on T-lymphocyte function and the mechanism of this effect

Whether recombinant human granulocyte colony-stimulating factor (rhG-CSF) affects lymphocyte function directly or indirectly is controversial. In this study, we found that T-cell proliferation was decreased considerably in response to phytohemagglutinin in donors who received rhG-CSF but was partly restored after monocytes were removed. Intracellular cytokine staining revealed that the interferon gamma-interleukin 4 ratio decreased by 5.97-fold in donor CD4(+) cells after rhG-CSF treatment. No effect of rhG-CSF on ex vivo T-cell function was observed. rhG-CSF indirectly induced significant quantitative and qualitative changes on lymphocytes, including a decrease in T-cell proliferation and type 2 helper T-cell polarization of the cytokine profile. Although monocytes suppressed T-cell proliferation, the suppressive activity induced by the quantitative change in monocyte numbers cannot completely account for the hyporesponsiveness of T-lymphocytes. We believe that there must be another mediating factor. In addition, the numbers and mean fluorescence intensities of CD14(+)CD86(+) cells and CD19(+)CD80(+) cells declined significantly in the peripheral blood after rhG-CSF treatment. Suboptimal amounts of stimulatory signals provided by low expression levels of B7 molecules on antigen-presenting cells (monocytes, B-lymphocytes) may help explain the alteration in T-cell proliferation. In addition, the absolute counts of CD3(+)CD4(-)CD8(-) cells in the peripheral blood were markedly increased and enriched in leukapheresis products following G-CSF treatment. These suppressor cells may contribute to T-cell hyporesponsiveness.