Precise prediction of a dominant class I MHC-restricted epitope of Listeria monocytogenes.

Listeria monocytogenes is a Gram-positive bacterium which grows in the cytoplasm of eukaryotic cells and can cause severe disease in immunocompromised individuals. In murine systems CD8+ T lymphocytes have been shown to be important effectors of acquired protective immunity against L. monocytogenes. Class I MHC-restricted CD8+ cytotoxic T lymphocytes (CTL), which lyse J774 macrophage-like targets infected with L. monocytogenes, are induced following in vivo injection of live organisms. Natural peptide epitopes derived from L. monocytogenes can be acid-extracted from heavily infected BALB/c spleens and detected by CTL. A CTL clone, B9, derived from a (BALB/c x C57BL/6)F1 (H-2dxb) mouse, recognizes one of these natural epitopes in an H-2Kd-restricted fashion. B9 also recognizes P815 (H-2d) mastocytoma cells transfected with the listeriolysin gene. To identify the region of the listeriolysin recognized by CTL we used the H-2Kd peptide-binding motif described by Rammensee and colleagues to synthesize 11 nonamer peptides. One of these peptides, listeriolysin 91-99, was recognized very efficiently by B9. This represents the first identified class I MHC-restricted epitope of bacteria and demonstrates the utility of the allele-specific motif for predicting CTL epitopes.     

Vancomycin-resistant enterococci exploit antibiotic-induced innate immune deficits

Infection with antibiotic-resistant bacteria, such as vancomycin-resistant Enterococcus (VRE), is a dangerous and costly complication of broad-spectrum antibiotic therapy. How antibiotic-mediated elimination of commensal bacteria promotes infection by antibiotic-resistant bacteria is a fertile area for speculation with few defined mechanisms. Here we demonstrate that antibiotic treatment of mice notably downregulates intestinal expression of RegIIIgamma (also known as Reg3g), a secreted C-type lectin that kills Gram-positive bacteria, including VRE. Downregulation of RegIIIgamma markedly decreases in vivo killing of VRE in the intestine of antibiotic-treated mice. Stimulation of intestinal Toll-like receptor 4 by oral administration of lipopolysaccharide re-induces RegIIIgamma, thereby boosting innate immune resistance of antibiotic-treated mice against VRE. Compromised mucosal innate immune defence, as induced by broad-spectrum antibiotic therapy, can be corrected by selectively stimulating mucosal epithelial Toll-like receptors, providing a potential therapeutic approach to reduce colonization and infection by antibiotic-resistant microbes.