Titer dynamic analysis of D29 within MTB-infected macrophages and effect on immune function of macrophages

The use of mycobacteriophage D29 to treat Mycobacterium tuberculosis (MTB)-infected macrophages results in significant inhibitory activity. This study aims to explore the novel treatment strategy of intracellular mycobacterial infection from the point of view of phages. We investigated the dynamic phagocytosis and elimination of D29 by macrophages, measured the titer of D29 inside and outside MTB within macrophages by fluorescence quantitative PCR, and detected the levels of interleukin 12 (IL-12) and nitric oxide (NO) in the culture supernatants of D29-infected macrophages by ELISA. Results showed that the activity of D29 phagocytosed by macrophages was significantly lower than that of D29 phagocytosed by MTB-infected macrophages. The titer of D29 that infected intracellular MTB ranged from 10(9) pfu to 10(4) pfu. The titer of D29 inside and outside intracellular MTB transiently increased when MTB-infected macrophages were incubated with D29 for 40 and 50 min; then, a large number of D29 were eliminated by macrophages. The levels of IL-12 and NO had no significant differences versus the negative control but were significantly lower compared with the lipopolysaccharide (LPS) positive control. These results suggest D29 has no effect on the immune function of macrophages and that high phage titer must be administered repeatedly if D29 is applied to treat intracellular MTB infection.