Ahmed Metwali

Heligmosomoides polygyrus inhibits established colitis in IL-10-deficient mice

Inflammatory bowel disease (IBD) is prevalent in industrialized countries, but rare in less‐developed countries. Helminths, common in less‐developed countries, may induce immunoregulatory circuits protective against IBD. IL‐10–/– mice given piroxicam develop severe and persistent colitis. Lamina propria mononuclear cells from colitic IL‐10–/– mice released IFN‐γ and IL‐12. The ongoing piroxicam‐induced colitis could be partially blocked with anti‐IL‐12 monoclonal antibody suggesting that the inflammation was at least partly IL‐12 dependent. Colonization of piroxicam‐treated colitic IL‐10–/– mice with Heligmosomoides polygyrus (an intestinal helminth) suppressed established inflammation and inhibited mucosal IL‐12 and IFN‐γ production. H. polygyrus augmented mucosal IL‐13, but not IL‐4 or IL‐5 production. Transfer of mesenteric lymph node (MLN) T cells from IL‐10–/– animals harboring H. polygyrus into colitic IL‐10–/– recipients inhibited colitis. MLN T cells from worm‐free mice did not. Foxp3 (scurfin) drives regulatory T cell function. H. polygyrus enhanced Foxp3 mRNA expression in MLN T cells that had regulatory activity. This suggests that H. polygyrus inhibits ongoing IL‐10–/– colitis in part through blocking mucosal Th1 cytokine production. Resolution of inflammation is associated with increased IL‐13 production and can be adoptively transferred by MLN T cells.

Eosinophils within the healthy or inflamed human intestine produce substance P and vasoactive intestinal peptide

The purpose of this study was to show if inflammatory cells within healthy or diseased human intestinal mucosa produce some regulatory neuropeptides. First, inflammatory cells were isolated from the intestinal lamina propria of 11 patients with ulcerative colitis or Crohns disease. Also collected were cells from anatomically normal intestine derived from five patients requiring bowel resection for diseases not related to inflammatory bowel disease. Extracts of these isolated cells contained authentic substance P (SP) and vasoactive intestinal peptide (VIP) as shown by RIA and their elution profiles on HPLC. Immunostaining of cells from nine of 13 additional patients localized immunoreactive SP and VIP to secretory granules within most mucosal eosinophils. No other cell types stained positive. Messenger RNA encoding SP and VIP was localized to lamina propria eosinophils by in situ hybridization. Mucosa inflammatory cells, from eight of nine more patients, cultured in vitro, released detectable amounts of VIP, but not SP. It is concluded that intestinal eosinophils produce SP and VIP. Since the eosinophils store and release more VIP than SP, it is possible that VIP is the preferred secretory product.

Colonization with Heligmosomoides polygyrus Suppresses Mucosal IL-17 Production

Helminth exposure appears to protect hosts from inappropriate inflammatory responses, such as those causing inflammatory bowel disease. A recently identified, strongly proinflammatory limb of the immune response is characterized by T cell IL-17 production. Many autoimmune type inflammatory diseases are associated with IL-17 release. Because helminths protect from these diseases, we examined IL-17 production in helminth-colonized mice. We colonized mice with Heligmosomoides polygyrus, an intestinal helminth, and analyzed IL-17 production by lamina propria mononuclear cells (LPMC) and mesenteric lymph node (MLN) cells. Colonization with H. polygyrus reduces IL-17A mRNA by MLN cells and inhibits IL-17 production by cultured LPMC and MLN cells. Helminth exposure augments IL-4 and IL-10 production. Blocking both IL-4 and IL-10, but not IL-10 alone, restores IL-17 production in vitro. Colonization of colitic IL-10-deficient mice with H. polygyrus suppresses LPMC IL-17 production and improves colitis. Ab-mediated blockade of IL-17 improves colitis in IL-10-deficient mice. Thus, helminth-associated inhibition of IL-17 production is most likely an important mechanism mediating protection from inappropriate intestinal inflammation.

Heligmosomoides polygyrus Promotes Regulatory T-Cell Cytokine Production in the Murine Normal Distal Intestine

ABSTRACT Helminths down-regulate inflammation and may prevent development of several autoimmune illnesses, such as inflammatory bowel disease. We determined if exposure to the duodenal helminth Heligmosomoides polygyrus establishes cytokine pathways in the distal intestine that may protect from intestinal inflammation. Mice received 200 H. polygyrus larvae and were studied 2 weeks later. Lamina propria mononuclear cells (LPMC) were isolated from the terminal ileum for analysis and in vitro experiments. Mice with H. polygyrus were resistant to trinitrobenzenesulfonic acid (TNBS)-induced colitis, a Th1 cytokine-dependent inflammation. Heligmosomoides polygyrus did not change the normal microscopic appearance of the terminal ileum and colon and minimally affected LPMC composition. However, colonization altered LPMC cytokine profiles, blocking gamma interferon (IFN-γ) and interleukin 12 (IL-12) p40 release but promoting IL-4, IL-5, IL-13, and IL-10 secretion. IL-10 blockade in vitro with anti-IL-10 receptor (IL-10R) monoclonal antibody restored LPMC IFN-γ and IL-12 p40 secretion. IL-10 blockade in vivo worsened TNBS colitis in H. polygyrus-colonized mice. Lamina propria CD4+ T cells isolated from colonized mice inhibited IFN-γ production by splenic T cells from worm-free mice. This inhibition did not require cell contact and was dependent on IL-10. Heligmosomoides polygyrus colonization inhibits Th1 and promotes Th2 and regulatory cytokine production in distant intestinal regions without changing histology or LPMC composition. IL-10 is particularly important for limiting the Th1 response. The T-cell origin of these cytokines demonstrates mucosal regulatory T-cell induction.

SSTR2A is the dominant somatostatin receptor subtype expressed by inflammatory cells, is widely expressed and directly regulates T cell IFN-γ release

Macrophages secrete the immunoregulatory peptide somatostatin (SOM) that inhibits IFN‐γ release by splenocytes and granuloma cells of schistosome‐infected mice. In this report we demonstrate that granuloma cells express mRNA for the SOM receptor SSTR2 but not the other four SSTR subtypes. Blocking SSTR2 activity with anti‐SSTR2 antiserum prevents SOM inhibition of T cell IFN‐γ production. This demonstrates that SOM regulates T cell function via SSTR2. Two isoforms of SSTR2 exist due to alternative RNA splicing. We developed sensitive and specific competitive PCR assays to quantify total SSTR2, SSTR2A and SSTR2B mRNA levels. The SSTR2A isoform accounts for 99 % of inflammatory cell SSTR2 mRNA and does not appear to be regulated at the transcripitonal level. B cells and macrophage cell lines also express SSTR2 mRNA which raises the possibility that SOM influences T cell IFN‐γ release by regulating accessory cell function. We show that SOM acts directly on T cells to inhibit TCR‐stimulated IFN‐γ release. Thus, SOM may directly regulate T cell IFN‐γ release at inflammatory sites.

Cutting Edge: Hemokinin Has Substance P-Like Function and Expression in Inflammation

Substance P (SP) belongs to the tachykinin family of molecules. SP, cleaved from preprotachykinin A, is a neuropeptide and a proinflammatory leukocyte product. SP engages neurokinin 1 receptor (NK-1R) to stimulate cells. Hemokinin (HK) is another tachykinin that binds NK-1R. HK comes from preprotachykinin C, which is distinct from preprotachykinin A. We determined whether HK functions like SP at inflammatory sites. Preprotachykinin C mRNA was in murine schistosome granulomas and intestinal lamina propria mononuclear cells. Granuloma T cells and macrophages expressed preprotachykinin C mRNA. HK bound granuloma T cell NK-1R with high affinity. SP and HK stimulated IFN-γ production with equal potency. NK-1R antagonist blocked the effect of SP and HK on IFN-γ secretion. Thus, both HK and SP are expressed at sites of chronic inflammation and share cell origin, receptor, and immunoregulatory function. Two distinct but functionally overlapping tachykinins govern inflammation through NK-1R at sites of chronic inflammation.

Substance P Regulates Th1-Type Colitis in IL-10 Knockout Mice

Substance P (SP) is a proinflammatory molecule that interacts with a neurokinin 1 receptor (NK-1R), which is on T cells and helps control IFN-γ production. IL-10−/− mice given a nonsteroidal anti-inflammatory drug (NSAID) develop Th1 colitis. We studied the importance of SP and NK-1R in this colitis model. LP T cells were isolated to study their NK-1R expression. LP T cells from IL-10−/− mice expressed NK-1R and produced IFN-γ only after NSAID treatment and induction of colitis. LP T cells from NSAID-treated wild-type controls or from age-matched untreated IL-10−/− animals did not express NK-1R or produce IFN-γ. Experiments showed that IL-12 induced NK-1R transcription in CD4+ T cells cultured in vitro. However, T cells cultured with IL-12 and IL-10 did not express NK-1R. IL-10 also down-modulated ongoing NK-1R expression. Mice given NK-1R antagonist after NSAID induction of severe colitis showed nearly complete reversal of inflammation, and LP T cells ceased IFN-γ secretion. Thus, intestinal inflammation in IL-10−/− mice is associated with the appearance of NK-1R in mucosal T cells, and an interplay between IL-12 and IL-10 regulates T cell NK-1R transcription. NK-1R antagonist reverses ongoing intestinal inflammation attesting to the importance of SP and its receptor in mucosal inflammation.

IL-18 and IL-12 Signal Through the NF-κB Pathway to Induce NK-1R Expression on T Cells

Substance P engages the T cell neurokinin 1 receptor (NK-1R) to enhance IFN-γ production. NK-1R on T cells is inducible. We studied mechanisms regulating T cell NK-1R expression. Murine splenocytes were cultured for 4 h with or without rIL-12 or rIL-18. Both IL-12 and IL-18 induced splenic T cells to express NK-1R transcripts. Induction was blocked by actinomycin D, but not cycloheximide, suggesting that protein synthesis was not required for initiation of NK-1R gene transcription. Inhibition of T cell NF-κB activation or NF-κB nuclear translocation also blocked NK-1R transcription. IL-12 and IL-18 strongly induce NK-1R mRNA expression in splenocytes from Stat4−/− mice, suggesting that the Stat4 pathway was not required for the induction of NK-1R transcription. Splenic T cells exposed to IL-12 or IL-18 in the presence of IL-10 expressed no NK-1R mRNA. However, TGFβ did not prevent NK-1R mRNA expression. Thus, IL-12 and IL-18 induce T cells to express NK-1R through NF-κB activation. IL-10, a regulator of the Th1 response, blocks this activation. These data further suggest that SP and NK-1R, which promote IFN-γ synthesis, are part of the Th1 pathway of immunity.

Murine mucosal T cells have VIP receptors functionally distinct from those on intestinal epithelial cells

Reports suggest that vasoactive intestinal peptide (VIP) binds to lymphocytes and modulates immune responses. The intestines are richly innervated with VIP-producing nerves. Thus, VIP from nerves or other sources may participate in mucosal immunoregulation. To explore this hypothesis further, murine intestinal mucosal inflammatory cells were scrutinized for functional VIP receptors. An [125I]VIP competitive binding assay characterized VIP receptors. Unfractionated lamina propria inflammatory cells bound [125I]VIP specifically. This binding was abrogated by T cell depletion. The VIP receptor on lamina propria T cells was of a single class with a Kd of 9.08 x 10(-9) M. It bound PHI and other peptide analogs poorly. The intestinal epithelial cell had a high-affinity VIP receptor (Kd 4.17 x 10(-10) M) that bound one VIP analog with moderate affinity. Both VIP and ConA stimulated mucosal inflammatory cells to release interleukin-5 (IL-5). Mucosal inflammatory cells depleted of T cells did not release IL-5 in response to VIP or ConA. It is concluded that: (1) some murine mucosal T lymphocytes have VIP receptors that may be distinct from those displayed on mucosal epithelial cells; (2) VIP affects mucosal T lymphocyte function.

IL-12 Induction of mRNA Encoding Substance P in Murine Macrophages from the Spleen and Sites of Inflammation

Substance P (SP), a neuropeptide, interacts with the neurokinin 1 receptor (NK-1R) on immune cells to help control IFN-γ production. In murine schistosomiasis mansoni, schistosome worms produce ova that incite focal Th2-type granulomatous inflammation within the liver and intestines. Normal gut is characterized by a controlled state of inflammation. IL-10 knockout mice develop chronic Th1-type colitis spontaneously. Both schistosome granulomas and gut mucosa display an SP immune regulatory circuit. However, the origin and regulation of SP production at these sites of inflammation are poorly understood. Macrophages are a potential source of SP. We therefore studied macrophages (F4/80+) from these models of inflammation. SP mRNA (preprotachykinin A (PPT A)) was detected within the schistosome granuloma, spleen, and lamina propria macrophages. Compared with those from wild-type mice, granuloma macrophages from STAT6−/− mice had 10-fold higher PPT A mRNA expression, whereas in STAT4−/− animals, PPT A mRNA expression was nearly abolished. IL-12 signals via STAT4 to induce Th1-type inflammation. It was demonstrated that IL-12, but not IL-18, induces SP mRNA expression in resting splenic macrophages from Schistosoma-infected mice and in wild-type lamina propria mononuclear cells. Thus, macrophages are a source for SP at these sites of chronic inflammation, and IL-12 and STAT4 are regulators of macrophage SP mRNA expression.