Antigen/IgG immune complex-primed mucosal mast cells mediate antigen-specific activation of co-cultured T cells

Reducing IgG accumulation via neonatal Fc receptor (FcRn) blockade relieves neuropathic pain

Preclinical and clinical studies have established that autoreactive immunoglobulin G (IgG) can drive neuropathic pain. We recently demonstrated that sciatic nerve chronic constriction injury (CCI) in male and female mice results in the production of pronociceptive IgG, which accumulates around the lumbar region, including within the dorsal root ganglia (DRG) and spinal cord, facilitating the development of neuropathic pain. These data raise the intriguing possibility that neuropathic pain may be alleviated by reducing the accumulation of IgG. To this end, we tested whether biologic inhibition or genetic deletion of the neonatal Fc receptor (FcRn) would attenuate mechanical hypersensitivity (allodynia) and IgG deposition induced by CCI. FcRn are prominently expressed on myeloid and endothelial cells and extend the half-life of IgG via pinocytosis and recycling into the extracellular milieu. We show here that administration of the FcRn blocker efgartigimod either 7- or 28-days post-CCI relieved allodynia among both male and female mice, compared to the Fc fragment control. Efgartigimod, administered systemically (intraperitoneal) or to the lumbar region (intrathecal), attenuated mechanical allodynia for at least one month. CCI-induced allodynia was similarly reduced in FcRn-deficient (FcRn-) mice compared to wild-type mice. Biologic inhibition or genetic deletion of FcRn also reduced CCI-induced accumulation of IgG on macrophages and neurons in lumbar DRG, as well as microglia in the lumbar dorsal spinal cord. Expression of the Fc receptor γ subunit (FcRγ) was reduced in efgartigimod-treated or FcRn- mice post-CCI compared to controls. The FcRγ subunit is a key component of Fc gamma receptors (FcγRs), which are activated by IgG immune complexes. In macrophage cultures stimulated by IgG immune complexes, FcRn blockade also dampened FcγR-dependent production of proinflammatory cytokines. Collectively, our study demonstrates that FcRn blockade or deletion alleviates mechanical allodynia and reduces IgG accumulation after CCI, attenuating pronociceptive IgG-FcγR signaling around the lumbar region. Strategies to block FcRn and reduce IgG recycling warrant further investigation as potential treatments for IgG-mediated neuropathic pain.

MHC Class II-Expressing Mucosal Mast Cells Promote Intestinal Mast Cell Hyperplasia in a Mouse Model of Food Allergy

BACKGROUND

IgE-mediated food allergy is accompanied by mucosal mast cell (MMC) hyperplasia in the intestinal mucosa. Intestinal MMC numbers correlate with the severity of food allergy symptoms. However, the mechanisms by which MMCs proliferate excessively are poorly understood. Here, we clarify the role of newly identified MHC class II (MHCII)-expressing MMCs in the effector phase of IgE-mediated food allergy.

METHODS

Mice reconstituted with MHCII-deficient or wild-type MMCs were used to generate a mouse mode of IgE-mediated food allergy. We assessed the extent of intestinal MMC hyperplasia and the severity of hypothermia in these mice. In addition, we performed in vitro antigen presentation assay using induced MHCII-expressing MMCs generated from bone marrow cells to evaluate the effect of CD4+ T cell activation on MMC proliferation.

RESULTS

In food-allergic mice, we identified the appearance of MHCII-expressing MMCs in the intestinal mucosa and showed that MMC hyperplasia was suppressed in mice with MHCII-deficient MMCs compared to mice with wild-type MMCs. In vitro assays demonstrated that MHCII-expressing MMCs incorporate food antigens directly and through the high-affinity IgE receptor FcεRI-mediated endocytosis and activate antigen-specific CD4+ T cells from food-allergic mice by antigen presentation. Activated CD4+ T cells secrete IL-4 and large amounts of IL-5, which enhance production of the mast cell growth factor IL-9 by IL-33-activated MMCs. Excess IL-9 causes excessive MMC proliferation, leading to the development of MMC hyperplasia.

CONCLUSION

Antigen presentation to CD4+ T cells by MHCII-expressing MMCs triggers intestinal MMC hyperplasia and exacerbates IgE-mediated food allergy.

Lung ILC2s are activated in BALB/c mice born to immunized mothers despite complete protection against respiratory syncytial virus

Activated lung ILC2s produce large quantities of IL-5 and IL-13 that contribute to eosinophilic inflammation and mucus production following respiratory syncytial virus infection (RSV). The current understanding of ILC2 activation during RSV infection, is that ILC2s are activated by alarmins, including IL-33, released from airway epithelial cells in response to viral-mediated damage. Thus, high levels of RSV neutralizing maternal antibody generated from maternal immunization would be expected to reduce IL-33 production and mitigate ILC2 activation. Here we report that lung ILC2s from mice born to RSV-immunized dams become activated despite undetectable RSV replication. We also report, for the first time, expression of activating and inhibitory Fcgamma receptors on ILC2s that are differentially expressed in offspring born to immunized versus unimmunized dams. Alternatively, ex vivo IL-33-mediated activation of ILC2s was mitigated following the addition of antibody: antigen immune complexes. Further studies are needed to confirm the role of Fcgamma receptor ligation by immune complexes as an alternative mechanism of ILC2 regulation in RSV-associated eosinophilic lung inflammation.

Human placental extract suppresses mast cell activation and induces mast cell apoptosis

BACKGROUND

Human placental extract (HPE) has been documented to facilitate the healing of certain disorders including allergy. However, the effects of HPE on the functionality of mast cells, a critical cell type in allergic diseases, have not been reported.

METHODS

To investigate the effects of HPE on the regulation of allergy with respect to the biological functions of mast cells, the mast cell line C57 or HMC-1 cells were treated with HPE followed by the assessment of cell proliferation, apoptosis, activation, chemotaxis and phagocytosis. Mouse peritoneal mast cells were also investigated for their responses to induction of apoptosis by HPE in vivo. Furthermore, the effect of HPE on mast cell degranulation was confirmed using the passive cutaneous anaphylaxis (PCA) assay, an acute allergy model.

RESULTS

HPE was capable of suppressing mast cell proliferation and inducing mast cell apoptosis. Mast cell degranulation in response to compound 48/80- or anti-DNP IgE and DNP-mediated activation was suppressed. In addition, treatment with HPE compromised the production of cytokines by mast cells and cell chemotaxis. These observations were consistent with the dampened passive cutaneous anaphylaxis (PCA) assay following treatment with HPE.

CONCLUSION

This study revealed a suppressive effect of HPE on overall mast cell activities, suggesting a potential regulatory role of HPE on the alleviation of allergic diseases through mast cells.

Glyconectin Cell Adhesion Epitope, β-d-GlcpNAc3S-(1→3)-α-l-Fucp, Is Involved in Blastulation of Lytechinus pictus Sea Urchin Embryos

Glycans, as the most peripheral cell surface components, are the primary candidates to mediate the initial steps of cell recognition and adhesion via glycan-glycan binding. This molecular mechanism was quantitatively demonstrated by biochemical and biophysical measurements at the cellular and molecular level for the glyconectin 1 β-d-GlcpNAc3S-(1→3)-α-l-Fucp glycan structure (GN1). The use of adhesion blocking monoclonal antibody Block 2 that specifically recognize this epitope showed that, besides Porifera, human colon carcinoma also express this structure in the apical glycocalyx. Here we report that Block 2 selectively immune-precipitate a Mr 580 × 103 (g580) acidic non-glycosaminoglycan glycan from the total protein-free glycans of Lytechinus pictus sea urchin hatched blastula embryos. Immuno-fluorescence confocal light microscopy and immunogold electron microscopy localized the GN1 structure in the apical lamina glycocalyx attachments of ectodermal cells microvilli, and in the Golgi complex. Biochemical and immune-chemical analyses showed that the g580 glycan is carrying about 200 copies of the GN1 epitope. This highly polyvalent g580 glycan is one of the major components of the glycocalyx structure, maximally expressed at hatched blastula and gastrula. The involvement of g580 GN1 epitope in hatched blastula cell adhesion was demonstrated by: (1) enhancement of cell aggregation by g580 and sponge g200 glycans, (2) inhibition of cell reaggregation by Block 2, (3) dissociation of microvilli from the apical lamina matrix by the loss of its gel-like structure resulting in a change of the blastula embryonal form and consequent inhibition of gastrulation at saturating concentration of Block 2, and (4) aggregation of beads coated with the immune-purified g580 protein-free glycan. These results, together with the previous atomic force microscopy measurements of GN1 binding strength, indicated that this highly polyvalent and calcium ion dependent glycan-glycan binding can provide the force of 40 nanonewtons per single ectodermal cell association of microvilli with the apical lamina, and conservation of glycocalyx gel-like structure. This force can hold the weight of 160,000 cells in sea water, thus it is sufficient to establish, maintain and preserve blastula form after hatching, and prior to the complete formation of further stabilizing basal lamina.

Mast cell degranulation and histamine release during A/H5N1 influenza infection in influenza-sensitized mice

Here we evaluate the role of mast cells in infection with influenza A/H5N1 virus in immunized mice. CBA mice were immunized intramuscularly with formalin-inactivated A/Vietnam/1194/2004 (H5N1)NIBRG-14 (H5N1). Serum samples were obtained on days 7, 12, 14, 21 after immunization. At day 14, the mice were infected intranasally with the A/Indonesia/5/2005 (H5N1)IDCDC-RG2 (H5N1) influenza virus with half of the animals receiving a mixture of the antihistamines. 67% of the vaccinated mice were protected from the lethality compared to 43% in the PBS-immunized group. Administration of antihistamines increased survival up to 85%–95%. Immunohistochemical examination using CD117 staining of the lungs demonstrated a larger quantity of activated mast cells after infection of immunized mice compared to mock-immunized mice. This was correlated to increased histamine level in the lungs and blood. Our experimental results suggest the involvement of mast cells and the histamine they produce in the pathogenesis of influenza infection in case of incomplete formation of the immune response to vaccination and mismatch of the vaccine and infection influenza viruses.

Helicobacter pylori Infection Increased Anti-dsDNA and Enhanced Lupus Severity in Symptomatic FcγRIIb-Deficient Lupus Mice

The defect on Fc gamma receptor IIb (FcγRIIb), the only inhibitory FcγR, has been identified as one of the genetic factors increasing susceptibility to lupus. The prevalence of Helicobacter pylori (HP) and FcγRIIb dysfunction-polymorphisms are high among Asians, and their co-existence is possible. Unfortunately, the influence of HP against lupus progression in patients with lupus is still controversial. In this study, the interactions between these conditions were tested with HP infection in 24-week-old FcγRIIb-/- mice (symptomatic lupus). HP induced failure to thrive, increased stomach bacterial burdens and stomach injury (histology and cytokines) in both wild-type and FcγRIIb-/- mice. While the severity of HP infection, as determined by these parameters, was not different between both strains, antibodies production (anti-HP, anti-dsDNA and serum gammaglobulin) were higher in FcγRIIb-/- mice compared to wild-type. Accordingly, HP infection also accelerated the severity of lupus as determined by proteinuria, serum creatinine, serum cytokines, renal histology, and renal immune complex deposition. Although HP increased serum cytokines in both wild-type and FcγRIIb-/- mice, the levels were higher in FcγRIIb-/- mice. As such, HP also increased spleen weight and induced several splenic immune cells responsible for antibody productions (activated B cell, plasma cell and follicular helper T cell) in FcγRIIb-/- mice, but not in wild-type. These data describe the different systemic responses against localized HP infection from diverse host genetic background. In conclusion, the mutual interactions between HP and lupus manifestations of FcγRIIb-/-mice were demonstrated in this study. With the prominent immune responses from the loss of inhibitory signaling in FcγRIIb-/- mice, HP infection in these mice induced intense chronic inflammation, increased antibody production, and enhanced lupus severity. Thus, the increased systemic inflammatory responses due to localized HP inducing gastritis in some patients with lupus may enhance lupus progression. More studies are needed.

Roles and relevance of mast cells in infection and vaccination

In addition to their well-established role in allergy mast cells have been described as contributing to functional regulation of both innate and adaptive immune responses in host defense. Mast cells are of hematopoietic origin but typically complete their differentiation in tissues where they express immune regulatory functions by releasing diverse mediators and cytokines. Mast cells are abundant at mucosal tissues which are portals of entry for common infectious agents in addition to allergens. Here, we review the current understanding of the participation of mast cells in defense against infection. We also discuss possibilities of exploiting mast cell activation to provide adequate adjuvant activity that is needed in high-quality vaccination against infectious diseases.