A pathogenic role of macrophages in mice intradermally infected with methicillin-resistant Staphylococcus aureus (37.18)

Abstract

Abstract In this study, intradermal MRSA infection in burn mice was pathogenically analyzed. Burn mice (3rd degree, 25% TBSA flame burn) and normal mice were infected i.d. with 108 CFU/mouse of MRSA, and abscesses formed in the infection sites and mortality rates of these mice were examined. Also, the abscess formation was examined in burn and normal mice after inoculation with F4/80+Mϕ isolated from tissues surrounding the infection sites of normal (N-F4/80 Mϕ) or burn mice (B-F4/80 Mϕ). Finally, these Mϕ were biophysically characterized. In the results, the abscess was formed in normal mice infected with MRSA and all of them survived. However, the abscess was not formed in burn mice infected with MRSA, and all of them died. The abscess was formed and sepsis was not developed in burn mice inoculated with N-F4/80 Mϕ. However, the abscess was not formed and sepsis was developed in normal mice inoculated with B-F4/80 Mϕ. N-F4/80 Mϕ produced IL-12 (but not IL-10) and were characterized as M1Mϕ, whereas B-F4/80 Mϕ produced IL-10 (but not IL-12) and were characterized as M2Mϕ. These results indicate that the abscess formation is a major host defense against MRSA i.d. infection. M1Mϕ at tissues surrounding the infection site play a pivotal role in the abscess formation. An abscess is not formed in burn mice predominated with M2Mϕ, which are inhibitory on the M1Mϕ generation. This study was supported by SHC NA #8840. A.A was supported by The James W. McLaughlin Fellowship Fund.