Impaired chemotactic responsiveness of macrophages from gnotobiotic rats.

Peptone-induced macrophages obtained from gnotobiotic (GB) rats responded poorly to chemotactic stimuli that have a powerful, attractive influence upon the cells of conventional donors. Monocyte recruitment from the circulation into peptone-induced exudates also was impaired in GB subjects. Although relatively more resident cells are present in exudates borne by GB donors, their number cannot in itself account for the sluggish response of peptone-induced cells from GB rats. Neutrophil accumulation in the inflamed peritoneal cavities and their responsiveness in vitro were similar in GB and conventional rats. The levels of serum-derived chemotactic factors were similar in such animals. Furthermore, germ-free rats exhibited no obvious defects in their capacity to generate lymphocyte-dependent monocyte chemotactic activity in situ upon specific stimulation with Listeria monocytogenes. It is suggested that the diminished chemotactic responsiveness of exudate macrophages is related in some way to the level of cell activation. This state of affairs might account for the impairment of delayed-type hypersensitivity in GB animals and their inability to resist intracellular bacterial infections.