Colony‐Stimulating Factors Increase Resistance to Atypical Mycobacteria in Resistant Mice, Whereas They Decrease Resistance in Susceptible Strains of Mice

Inbred strains of mice, notably the susceptible C57BL/6 and the resistant A/J strains of mice, were infected with a strain of Mycobacterium avium. The infection in the visceral organs of mice was then studied, and the effect of colony‐stimulating factors, i.e., interleukin‐3 (IL‐3), granulocyte‐macrophage colony‐stimulating factor (GM‐CSF), and macrophage colony‐stimulating factor (CSF‐1) on the infectious process was evaluated. Infusion of GM‐CSF, CSF‐1, and IL‐3 led to a significant, albeit rather modest, increase in the mycobacterial resistance of A/J mice, as seen by a decrease in the number of colony‐forming units (CFU) in the organs. Conversely, these CSFs dramatically increased the susceptibility of C57BL/6 mice, as seen by increased bacterial numbers in the spleens and livers. In vitro studies demonstrated that resident peritoneal macrophages from susceptible mice were more permissive than cells from resistant mice for mycobacterial growth. Application of CSFs on peritoneal macrophage monolayers led to an increased growth in both A/J and C57BL/6 monolayers for IL‐3 and CSF‐1 and a small microbiostatic effect for GM‐CSF. Cytokine treatment did not, however, change the resistance/ susceptibility phenotype of isolated macrophages. Our results indicate that CSFs may exert beneficial or detrimental effects on resistance to mycobacteria depending on the host genetic make up.