Azithromycin alters Colony Stimulating Factor-1R (CSF-1R) expression and functional output of murine bone marrow-derived macrophages: A novel report

Antibiotic treatment may lead to side effects that require mechanistic explanation. We investigated the effect of azithromycin (AZM) treatment on bone marrow-derived macrophage (M & phi;) generation, their functional output, and the subsequent effect on bacterial clearance in a mouse model of S. flexneri infection. To our fascination, AZM increased PU.1, C/EBP & beta;, CSF-1R/pCSF-1R expressions leading to M2-skewed in vitro BMDM generation. Altered M & phi;-functions like- phagocytosis, oxidative stress generation, inflammasome-activation, cytokine release, and phenotype (pro-inflammatory-M1, anti-inflammatory-M2) even in the presence of infection were observed with AZM treatment. AZM increased CD206, egr2, arg1 (M2-marker) expression and activity while reducing CD68, inducible nitric oxide (iNOS) expression, and activity (M1-marker) in M & phi;s during infection. Proinflammatory cytokines (TNF-& alpha;, IL-12, IL-1 & beta;) were reduced and anti-inflammatory IL-10 release was augmented by AZM-treated-iM & phi;s (aiM & phi;s) along with decreased asc, nlrp3, aim2, nlrp1a, caspase1 expressions, and caspase3 activity signifying that aM & phi;s/aiM & phi;s were primed towards an anti-inflammatory phenotype. Interestingly, CSF-1R blockade increased NO, IL-12, TNF-& alpha;, IL-1 & beta;, decreased TGF-& beta; release, and CD206 expression in aiM & phi;s. T-cell co-stimulatory molecule cd40, cd86, and cd80 expressions were decreased in ai/aM1-M & phi;s and cocultured CD8+, CD4+ T-cells had decreased proliferation, t-bet, IFN-& gamma;, IL-17, IL-2 but increased foxp3, TGF-& beta;, IL-4 which were rescued with CSF-1R blockade. Thus AZM affected M & phi;-functions and subsequent T-cell responses independent of its antibacterial actions. This was validated in the balb/c model of S. flexneri infection. We conclude that AZM skewed BMDM generation to anti-inflammatory M2-like via increased CSF-1R expression. This warrants further investigation of AZM-induced altered-M & phi;-generation during intracellular infections.