Role of NleH, a type III secreted effector from attaching and effacing pathogens, in colonization of the bovine, ovine, and murine gut.

The human pathogen enterohemorrhagic Escherichia coli (EHEC) O157:H7 colonizes human and animal gut via formation of attaching and effacing lesions. EHEC strains use a type III secretion system to translocate a battery of effector proteins into the mammalian host cell, which subvert diverse signal transduction pathways implicated in actin dynamics, phagocytosis, and innate immunity. The genomes of sequenced EHEC O157:H7 strains contain two copies of the effector protein gene nleH, which share 49% sequence similarity with the gene for the Shigella effector OspG, recently implicated in inhibition of migration of the transcriptional regulator NF-kappaB to the nucleus. In this study we investigated the role of NleH during EHEC O157:H7 infection of calves and lambs. We found that while EHEC DeltanleH colonized the bovine gut more efficiently than the wild-type strain, in lambs the wild-type strain exhibited a competitive advantage over the mutant during mixed infection. Using the mouse pathogen Citrobacter rodentium, which shares many virulence factors with EHEC O157:H7, including NleH, we observed that the wild-type strain exhibited a competitive advantage over the mutant during mixed infection. We found no measurable differences in T-cell infiltration or hyperplasia in colons of mice inoculated with the wild-type or the nleH mutant strain. Using NF-kappaB reporter mice carrying a transgene containing a luciferase reporter driven by three NF-kappaB response elements, we found that NleH causes an increase in NF-kappaB activity in the colonic mucosa. Consistent with this, we found that the nleH mutant triggered a significantly lower tumor necrosis factor alpha response than the wild-type strain.

The p50 subunit of NF-kappaB is critical for in vivo clearance of the noninvasive enteric pathogen Citrobacter rodentium.

Citrobacter rodentium, a natural mouse pathogen, belongs to the family of extracellular enteric pathogens that includes enteropathogenic Escherichia coli (EPEC) and enterohemorrhagic E. coli (EHEC). C. rodentium shares many virulence factors with EPEC and EHEC and relies on attaching-and-effacing lesion formation for colonization and infection of the gut. In vivo, C. rodentium infection is characterized by increased epithelial cell proliferation, mucosal thickening, and a TH1-type immune response, but with protective immunity believed to be mediated by serum immunoglobulin G (IgG). In this work, we characterize the immune response and pathology of mice lacking the p50 subunit of the transcription factor nuclear factor kappa B (NF-kappaB) during C. rodentium infection. We show that p50(-/-) mice are unable to clear C. rodentium infection. Furthermore, these animals show a reduced influx of immune cells into infected colonic tissue and greater levels of mucosal hyperplasia and the cytokines tumor necrosis factor alpha and gamma interferon. Surprisingly, despite being unable to eliminate infection, p50(-/-) mice showed markedly higher levels of anti-Citrobacter IgG and IgM, suggesting that antibody alone is not responsible for bacterial clearance. These data also demonstrate that non-NF-kappaB-dependent defenses are insufficient to control C. rodentium infection, and hence, the NF-kappaB p50 subunit is critical for defense against this noninvasive pathogen.