IL-21: a new player in the control of isotype switch in Peyer's patches

Single-cell atlas of splenocytes reveals a critical role of a novel plasma cell‒specific marker Hspa13 in antibody class-switching recombination and somatic hypermutation

Our previous study had shown that member 13 (Hspa13) of heat shock protein family A (Hsp70) promotes plasma cell (PC) production and antibody secretion. To further explore Hspa13 expression and function, we combined single-cell RNA-sequencing and antigen receptor lineage (BCR) analysis to characterize sheep red cell‒primed splenocytes. The single-cell transcriptional profiles revealed that Hspa13 is specifically and highly expressed in PCs. These results suggest that Hspa13 is a novel PC-specific marker. In terms of its function, we found that the CD19^cre-mediated conditional knock-out (cKO) of Hspa13 reduced the expression of Ebi3 and IL-10 in PCs. Ebi3 and IL-10 are important factors in IL-4‒secreting type 2 helper T cell (Th2) activation and differentiation. As expected, we found that the Hspa13 cKO reduced IL‒4-expressing follicular helper T (Tfh2) cells. Finally, the single-cell antigen receptor analysis demonstrated that the Hspa13 cKO reduced the Aicda-mediated antibody class-switching recombination (CSR) and somatic hypermutation (SHM) in germinal centers (GCs) B cells. Altogether, the single-cell atlas of splenocytes revealed a critical indirect role for the novel PC-specific marker Hspa13 in CSR and SHM in GC B cells by promoting Ebi3 and IL-10 expression in PCs to induce IL-4-expressing Tfh2 cells. Further exploration of Hspa13 expression and function will provide valuable clues for how to use Hspa13 in the treatment of autoimmune diseases.

The role of Peyer's patches in synchronizing gut IgA responses

Because Peyer's patches (PP) are the main inductive sites for gut IgA responses we have focused this review on what we know about the function of PP germinal centers (GC). The vast majority of IgA gene sequences in the gut lamina propria (LP) are heavily mutated arguing for an origin in GC. Because PP GC formation is dependent on the presence of CD4 T cells, we speculate that all IgA responses in the normal gut are directly or indirectly T cell-dependent (TD). We hypothesize that the CD4 T cell involvement in gut IgA responses against the microbiota is different from that in systemic responses since cognate T-B cell interactions appear not to be required. In the absence of cognate interactions the function of CD4 follicular helper T cells (Tfh) in PP GC is unclear. However, production of IL-21 and IL-6 is more pronounced than in peripheral lymph nodes. Importantly, we discuss how multiple PP are involved in generating specific IgA responses to TD antigens given orally. Recently we found that oral immunization with NP-hapten conjugated to cholera toxin (NP-CT) stimulated a strong highly synchronized, oligoclonal and affinity matured IgA response. This was achieved through re-utilization of GC in multiple PP as GC IgA B cells emigrated into already established GC. Clonally related B cells were present in both inductive and effector lymphoid tissues in the gut and clonal trees involving multiple PP could be constructed in individual mice. Through adoptive transfer of B1-8(hi) NP-specific B cells we demonstrated that GL7(+) PP B cells could enter into pre-existing GC in PP, a process that was antigen-dependent but did not to require cognate Tfh interactions. Finally, we discuss the role of PP GC for the generation of memory B cells and long-lived plasma cells in the light of contrasting findings regarding IgA memory development to colonizing commensal bacteria versus that to oral immunization with enteropathogens or TD antigens.

Immunotherapy with oligomannose-coated liposomes ameliorates allergic symptoms in a murine food allergy model

BACKGROUND

Allergen-specific immunotherapy has been anticipated to be a disease-modifying therapy for food allergies. We previously reported that CD8(+) regulatory T cells may prevent antigen-sensitized mice from developing allergic diarrhea. Because oligomannose-coated liposomes (OML) have been shown to induce MHC class I-restricted CD8(+) T cell responses, we analyzed the adjuvant activities of OML for inducing regulatory CD8(+) T cells and mucosal tolerogenic responses in allergen-sensitized mice.

METHODS

The BALB/c mice that were previously sensitized to ovalbumin (OVA) were intranasally immunized with OVA-encased in OML (OVA-OML) or OVA-encased in non-coated liposomes (OVA-NL). We assessed allergic diarrhea induced by oral OVA administration, OVA-specific immunoglobulin production, and cytokine production in the intestines and mesenteric lymph nodes (MLNs).

RESULTS

Intranasal immunization with OVA-OML, but not OVA-NL, suppressed the development of allergic diarrhea. This was associated with in vitro Ag-induced IL-10 production and the in vivo expansion of CD8(+) CD28(-) and CD4(+) CD25(+) Foxp3(+) T cell populations among mesenteric lymph node mononuclear cells, and was significantly ablated by anti-SIGNR1 or anti-CR3 mAbs. Up-regulation of serum OVA-specific IgE was suppressed, whereas OVA-specific IgG1, IgG2a, and soluble IgA production were enhanced by intranasal administration of OVA-OML. Adoptive transfer of CD8(+) CD28(-) T cells but not CD28(+) CD8(+) T cells from the MLNs of OVA-OML-treated mice ameliorated the development of diarrhea.

CONCLUSION

These results suggest that intranasal immunization with Ag-encased OML may be an effective immunotherapy for food allergies, as it induces a subset of regulatory CD8(+) T cells as well as CD4(+) CD25(+) Foxp3(+) T cell and modulates humoral immune responses in allergen-sensitized mice.

Tolerance and protection against infection in the genital tract

The genital tract is a unique immunological environment that must support the reproductive function and resist infection. Particularly in the female tract, immunoregulatory and immunosuppressive activities that permit the growth of the fetus create an environment that can readily be exploited by microbes that have become well-adapted to this location. Cellular and molecular mediators of immune responses differ from those found at other mucosal surfaces. Mechanisms of immune response induction and delivery, as well as immune effector functions at the genital mucosae need to be considered in the development of vaccines against infections of the genital tract.