Peripheral blood neutrophils of germ-free rats modified by in vivo granulocyte-colony-stimulating factor and exposure to natural environment.

Peripheral blood neutrophils from germ-free (GF), specific-pathogen-free (SPF) and conventional (CV) rats were compared. Besides neutropenia and impaired superoxide anion generation as previously reported, it was found that GF rats had lower phagocytic function (70%) and generated less nitric oxide than the other rats. GF and SPF rats were injected with recombinant human granulocyte-colony-stimulating factor (rhG-CSF), or were transferred to natural environment. It was found that total number, phagocytosis, intracellular killing, ratio of phagocytosis versus killing (killing efficiency) and nitric oxide production induced by recombinant rat interferon-gamma (rrIFN-gamma) were normalized upon injection of rhG-CSF. These results indicate that rhG-CSF may stimulate neutrophil production and induce the expression of neutrophil receptors for phagocytosis and nitric oxide production in GF rats. Although lower than in CV rats, the level of superoxide produced was sufficient for normal neutrophil-killing efficiency in SPF and GF rats. In SPF rats, this could be amended by exposure to natural environment. However, neither rhG-CSF injection nor transfer to natural environment could increase the generation of superoxide anion in GF rats.