A98-04 Immuno-modulatory Role of Microbial Metabolites in NTM Lung Infection

Abstract Rationale Despite prolonged antibiotics, NTM lung infection often persists and recurs, thus highlighting the importance of adjunctive treatment. Microbes elaborate metabolites such as short-chain fatty acids (SCFAs) and indole derivatives of tryptophan that can protect against infections. In this study, using both a cellular and a preclinical model, we explored the ability of SCFAs (butyrate and propionate) and indole-3-propionic acid (IPA, a tryptophan microbial metabolite) to modulate the immune inflammatory response and protect against NTM infection. Methods In-vitro, we infected THP-1 cells (pretreated with phorbol 12-myristate 13-acetate for 24h) with the MAC 101 strain at a multiplicity of infection of 1:1. Cells were lysed at 3h, 24h and 48h post-infection. For murine infections, we utilized the aerosol route with the MAC 101 strain in BALB/c mice at a concentration of 108 CFU/mL. Mice were euthanized at 4w post-infection. Lung homogenates were used for CFU enumeration. Flow cytometry was used to immunophenotype T-cells and PD-1 expression. Mouse lung BAL was used for ELISA-based detection of DNA-H3Cit complexes. Doses of butyrate and propionate were 200mM and IPA was 200mg/L in drinking water. Results NTM recovery from THP-1 cells treated with butyrate, propionate and IPA was reduced at 24h post-infection (p 0.01 butyrate, p 0.001 propionate, p 0.0001 IPA, Fig. 1A-C). At 48h, the recovery was reduced for propionate and IPA only (p 0.0001, Fig. 1B-C). In the preclinical model, lung CFU declined in all experimental arms treated with microbial metabolites at 4 weeks post-infection (Fig. 1D). This was accompanied by a decrease in neutrophil extracellular trap (NET) levels in groups treated with butyrate and IPA (p 0.01, Fig. 1E). On flow cytometry, CD4+ Th1 cells were reduced in all three groups (p 0.05 butyrate, propionate and IPA, Fig. 1G), but CD4+ Th17 cells were reduced only in the butyrate group (p 0.05, Fig. 1H). Expression of PD-1 receptor on CD4+ T cells was similarly reduced in all three groups (p 0.05, Fig. 1J), while expression of PD-1 receptor on CD8+ T cells was only reduced in the propionate and IPA groups (p 0.01 propionate, p 0.05 IPA, Fig. 1K). Conclusions Here, we show that microbial metabolites such as SCFAs and IPA can reduce NTM burden in both cellular and preclinical infection models. This is accompanied by modulation of the innate (NET) and adaptive immune responses. Our study indicates that further investigations into the potential role of these metabolites as adjunctive immuno-modulatory therapy in NTM lung disease are warranted. This abstract is funded by: American Thoracic Society, NIH