Antibacterial resistance of severely burned mice treated with an RORα selective inverse agonist

Abstract

Abstract In our previous studies, an antibacterial resistance of severely burned mice to enterococcal translocation has been improved by treatment with RORα selective agonist SR3335 (an inhibitor of ILC2 activation). Therefore, the effect of SR3335 against infections with P. aeruginosa (PA) and MRSA was studied in severely burned mice. Severely burned mice (30% TBSA burn) infected with PA (103 CFU/mouse, i.d.) or MRSA (106 CFU/mouse, i.v.) 3 days post burn injury were treated i.p. with 100 μg/mouse of SR3335 simultaneously, 1 and 2 days after the infection. The antibacterial effect of SR3335 was evaluated by bacterial growth in organs of these mice 3-5 days post-infection. In some experiments, lamina propria mononuclear cells (LPMC) were isolated from burned mice treated with or without SR3335, and analyzed for lin−CD127+ICOS+Sca-1+ cells (ILC2), F4/80+CD11b+IL-12+CD38+ cells (M1Mϕ), F4/80+CD11b+CD206+ cells (M2Mϕ), and Gr-1+CD11b+ cells (MDSC) by flow cytometry. In the results, PA and MRSA vigorously grew in various organs of burned mice. However, both of the pathogens did not grow in organs of the same mice treated with SR3335. The number of ILC2 increased greatly in the LPMC of burned mice, while this increase was not shown in these mice treated with SR3335. The numbers of M2Mϕ and MDSC increased in the LPMC of burned mice, while the numbers of these cells were not increased in the same mice treated with the compound. M1Mϕ were induced by CpG DNA in cultures of LPMC isolated from burned mice treated with SR3335. These results suggest that SR3335 improves the antibacterial resistance of severely burned mice against PA and MRSA through the modification of burn-associated appearance of ILC2, M2Mϕ, and MDSC.