Mutated major histocompatibility complex class II transactivator up-regulates interleukin-33-dependent differentiation of Th2 subset through Nod2 binding for NLR (NOD-like receptor) signaling initiation

NLRP3 regulates CIITA/MHC II axis and interferon-γ-inducible chemokines in Malassezia globosa-infected keratinocytes

CIITA, a member of NOD-like receptor (NLR) family, is the major MHC II trans-activator and mediator of Th1 immunity, but its function and interaction with NLRP3 have been little studied. We found activation of NLRP3 inflammasome, increased expression of CIITA, CBP, pSTAT1, STAT1, MHC II, IFN-γ and IFN-γ-inducible chemokines (CCL1 and CXCL8), and colocalisation of NLRP3 with CIITA in Malassezia folliculitis lesions, Malassezia globosa-infected HaCaT cells and mouse skin. CoIP with anti-CIITA or anti-NLRP3 antibody pulled down NLRP3 or both CIITA and ASC. NLRP3 silencing or knockout caused CIITA downexpression and their colocalisation disappearance in HaCaT cells and mouse skin of Nlrp3-/- mice, while CIITA knockdown had no effect on NLRP3, ASC, IL-1β and IL-18 expression. NLRP3 inflammasome inhibitors and knockdown significantly suppressed IFN-γ, CCL1, CXCL8 and CXCL10 levels in M. globosa-infected HaCaT cells. CCL1 and CXCL8 expression was elevated in Malassezia folliculitis lesions and reduced in Nlrp3-/- mice. These results demonstrate that M. globosa can activate NLRP3 inflammasome, CIITA/MHC II signalling and IFN-γ-inducible chemokines in human keratinocytes and mouse skin. NLRP3 may regulate CIITA by their binding and trigger Th1 immunity by secreting CCL1 and CXCL8/IL-8, contributing to the pathogenesis of Malassezia-associated skin diseases.

NOD2 drives early IL-33-dependent expansion of group 2 innate lymphoid cells during Crohn's disease-like ileitis

Innate lymphoid cells (ILCs) are enriched at barrier surfaces, including the gastrointestinal tract. While most studies have focused on the balance between pathogenic group 1 ILCs (ILC1s) and protective ILC3s in maintaining gut homeostasis and during chronic intestinal inflammation, such as Crohn's disease (CD), less is known regarding ILC2s. Using an established murine model of CD-like ileitis, i.e., the SAMP1/YitFc (SAMP) mouse strain, we showed that ILC2s, compared with ILC1s and ILC3s, were increased within draining mesenteric lymph nodes and ilea of SAMP versus AKR (parental control) mice early, during the onset of disease. Gut-derived ILC2s from CD patients versus healthy controls were also increased and expanded, similarly to ILC1s, in greater proportion compared with ILC3s. Importantly, we report that the intracellular bacteria-sensing protein, nucleotide-binding oligomerization domaining-containing protein 2, encoded by Nod2, the first and strongest susceptibility gene identified for CD, promoted ILC2 expansion, which was dramatically reduced in SAMP mice lacking NOD2 and in SAMP mice raised under germ-free conditions. Furthermore, these effects occurred through a mechanism involving the IL-33/ST2 ligand-receptor pair. Collectively, our results indicate a functional link between NOD2 and ILC2s, regulated by the IL-33/ST2 axis, that mechanistically may contribute to early events leading to CD pathogenesis.

A peptide tetramer Tk-tPN induces tolerance of cardiac allografting by conversion of type 1 to type 2 immune responses via the Toll-like receptor 2 signal-promoted activation of the MCP1 gene

The plant protein trichosanthin (Tk) and its derived peptide tetramer Tk-tPN have been shown to stimulate the type 2 immune responses for treating autoimmune disease. This work explores the possibility of using Tk-tPN as a non-toxic immunosuppressant to induce transplantation tolerance using the mechanisms by which T-cell-mediated immune responses are transferred from type 1 to type 2 through innate immunity-related pathways. Immunocytes and cytokine secretions involved in the mouse cardiac allografting model with Tk-tPN treatment were characterized. Identification of critical genes and analysis of their functions through Toll-like receptor (TLR) -initiated signalling and the possible epigenetic changes were performed. Mean survival times of the cardiac allografts were delayed from 7.7 ± 0.3 days (control) to 22.7 ± 3.9 days (P < 0.01) or 79.1 ± 19.2 days (P < 0.0001) when Tk-tPN was introduced into the recipients alone or together with rapamycin, respectively. The grafting tolerance was donor-specific. The secretion pattern of the type 1 cytokine/transcription factor (IL-2(+) IFN-γ(+) T-bet(+)), which is responsible for the acute graft rejection, was shifted to the type 2 factor (IL-4(+) IL-10(+) Gata3+), together with a selective expansion of the IL-4/IL-10-producing CD8+ CD28- regulatory T-cell subset. A TLR2-initiated high expression of chemokine gene MCP1 was detectable simultaneously. Epigenetically Tk/Tk-tPN could also acetylate the histone H3K9 of MCP1 promoter to skew the immunity towards T helper type 2 responses. Tk/Tk-tPN is therefore capable of down-regulating the type 1 response-dominant rejection of cardiac allografts by evoking type 2 immunity through the activation of a TLR2-initiated signalling pathway and MCP1 gene to expand the IL-4/IL-10-secreting CD8+ CD28- regulatory T cells. Tk-tPN could be a promising novel immunosuppressant to induce tolerance in allotransplantation.