Canine granulopoiesis: alterations induced by suppression of gram-negative flora.

We investigated alterations in canine granulopoiesis following suppression of bacterial flora by antibiotic treatment. Beagles were decontaminated in sterile isolation with laminar air flow, by an antifungal and antibiotic regimen. Skin and fecal specimen cultures were usually negative after 4 days. The reduction of gram-negative bacteria resulted in a significant decrease in plasma colony-stimulating factor (CSF) levels, marrow CFU-c concentration, and the cytopoietic activity of marrow-derived diffusion chamber (DC) progenitor cells. The period of conventionalization was characterized by a significant although delayed increase in plasma CSF as well as marked increases in marrow CFU-c concentration and cytopoietic activity of marrow DC progenitors. There was also mobilization of marrow DC progenitors into the circulation. All parameters returned to control values within 7 days of conventionalization. These data supported the hypothesis that the gram-negative bacteria of the gut play a significant role in the regulation of normal canine granulopoiesis.