Goblet Cell Derived RELM-β Recruits CD4+ T Cells during Infectious Colitis to Promote Protective Intestinal Epithelial Cell Proliferation

Abstract

Enterohemorrhagic Escherichia coli and related food and waterborne pathogens pose significant threats to human health. These attaching/effacing microbes infect the apical surface of intestinal epithelial cells (IEC), causing severe diarrheal disease. Colonizing the intestinal luminal surface helps segregate these microbes from most host inflammatory responses. Based on studies using Citrobacter rodentium, a related mouse pathogen, we speculate that hosts rely on immune-mediated changes in IEC, including goblet cells to defend against these pathogens. These changes include a CD4+ T cell-dependent increase in IEC proliferation to replace infected IEC, as well as altered production of the goblet cell-derived mucin Muc2. Another goblet cell mediator, REsistin-Like Molecule (RELM)-β is strongly induced within goblet cells during C. rodentium infection, and was detected in the stool as well as serum. Despite its dramatic induction, RELM-β’s role in host defense is unclear. Thus, wildtype and RELM-β gene deficient mice (Retnlb -/-) were orally infected with C. rodentium. While their C. rodentium burdens were only modestly elevated, infected Retnlb -/- mice suffered increased mortality and mucosal ulceration due to deep pathogen penetration of colonic crypts. Immunostaining for Ki67 and BrDU revealed Retnlb -/- mice were significantly impaired in infection-induced IEC hyper-proliferation. Interestingly, exposure to RELM-β did not directly increase IEC proliferation, rather RELM-β acted as a CD4+ T cell chemoattractant. Correspondingly, Retnlb -/- mice showed impaired CD4+ T cell recruitment to their infected colons, along with reduced production of interleukin (IL)-22, a multifunctional cytokine that directly increased IEC proliferation. Enema delivery of RELM-β to Retnlb -/- mice restored CD4+ T cell recruitment, concurrently increasing IL-22 levels and IEC proliferation, while reducing mucosal pathology. These findings demonstrate that RELM-β and goblet cells play an unexpected, yet critical role in recruiting CD4+ T cells to the colon to protect against an enteric pathogen, in part via the induction of increased IEC proliferation.

Resistin-like molecule β is a bactericidal protein that promotes spatial segregation of the microbiota and the colonic epithelium

“…This is consistent with the salt and pH sensitivity of other antimicrobial peptides (21) and likely reflects the fact that such antibacterial proteins have evolved to function in the acidic, low-salt environment that is present in the mucus layer (22). The requirement for these specialized conditions might also explain why RELMβ was previously reported to lack antibacterial activity (12). (14) showing the N-terminal α-helix and the C-terminal β-sheet with its aromatic residues.…”

“…S5B) and showed that C. rodentium infection led to higher numbers of tissue-associated bacteria in the absence of RELMβ (Fig. S5C), as previously reported (12).…”

“…For example, RELMβ-deficient mice show enhanced colonic expression of T H 2 cytokines and IL-17 (31), as well as decreased T cell recruitment during intestinal infection with C. rodentium and parasitic worms (7,12). It will be important to determine whether these effects are secondary to RELMβ-dependent alterations in the composition or location of intestinal microbial communities, or arise from cytokine-like activities of RELMβ that may be independent of its bactericidal function.…”

“…Initially, both RELMβ and resistin were characterized as hormones that modulate insulin action (10,11). However, subsequent studies revealed that RELMβ also plays a role in several aspects of host defense, including protection against infection by parasitic nematodes and Citrobacter rodentium (7,12). Although this has been attributed to cytokine-like activities of RELMβ, the mechanistic basis for RELMβ's contributions to host defense remains unclear.…”

Control of Giardiasis by Interleukin-17 in Humans and Mice—Are the Questions All Answered?

“…Additional comparisons of wild-type and IL-17A-deficient animals found that mice lacking IL-17A had significantly reduced fecal IgA levels both before and after infection, consistent with a role for IL-17 in inducing expression of the poly-Ig receptor that transports IgA from the serum into the intestinal lumen (15). IL-17A-deficient mice also had lower levels of mRNA encoding ␤-defensin-1, and IL-17RA-deficient mice had lower levels of mRNAs for resistin-like molecule ␤ (RELM-␤), serum amyloid A1 (Saa1), and serum amyloid A2 (Saa2), all proteins with potential antimicrobial and immunoregulatory functions (16)(17)(18)(19)(20).…”