The role of mast cells in allergy and autoimmunity

C1q governs deposition of circulating immune complexes and leukocyte Fcgamma receptors mediate subsequent neutrophil recruitment

Inflammation induced by circulating immunoglobulin G–immune complexes (ICs) characterizes many immune-mediated diseases. In this work, the molecular requirements for the deposition of circulating ICs and subsequent acute leukocyte recruitment in mice were elucidated. We show that after intravenous injection, preformed soluble ICs are rapidly deposited in the postcapillary venules of the cremaster microcirculation, secondary to increased vascular permeability. This deposition is dependent on complement C1q. IC deposition is associated with leukocyte recruitment. Leukocyte rolling, which is mediated by P-selectin in the exteriorized cremaster muscle, is not further increased in response to ICs. In contrast, leukocyte rolling velocity is significantly decreased and leukocyte adhesion is significantly increased in the presence of ICs. The IC-mediated slow leukocyte rolling velocity and subsequent adhesion and emigration are dependent on Fcγ receptors (FcγRs), particularly FcγRIII, with complement C3 and C5 having no detectable role. These studies suggest a regulatory mechanism of IC deposition and leukocyte trafficking in IC-mediated inflammation requiring C1q and FcγRs in sequential, noninteracting roles.

Attenuation of Th1 effector cell responses and susceptibility to experimental allergic encephalomyelitis in histamine H2 receptor knockout mice is due to dysregulation of cytokine production by antigen-presenting cells

Histamine, a biogenic amine with both neurotransmitter and vasoactive properties, is well recognized as an immunomodulatory agent in allergic and inflammatory reactions. It also plays a regulatory role in the development of antigen-specific immune responses. CD4+ T-cells from histamine H1 receptor (H1R)-deficient (H1RKO) mice produce significantly less interferon-gamma and more interleukin (IL)-4 in in vitro recall assays compared to wild-type controls. H1RKO mice are also less susceptible to acute early-phase experimental allergic encephalomyelitis indicating that H1R signaling in CD4+ T cells plays a central role in regulating pathogenic T-cell responses. In this study, we show that mice lacking histamine H2 receptor (H2RKO) are similar to H1RKO mice in that they develop encephalitogen-specific T-cell responses as assessed by proliferation and IL-2 production and present with less severe acute early-phase experimental allergic encephalomyelitis. However, unlike T cells from H1RKO mice, which exhibit a strong Th2 bias, T cells from H2RKO mice do not. Rather, they are uniquely characterized by a significant inhibition of Th1 effector cell responses. Given that both histamine and adjuvants such as pertussis toxin modulate antigen-presenting cell (APC) maturation and function, including T-cell-polarizing activity, we analyzed the cytokines/chemokines secreted by APCs from wild-type, H1RKO, and H2RKO mice. Significant differences in cytokine/chemokine production by APCs from unimmunized and immunized mice were delineated. APCs from H2RKO mice produce significantly less IL-12 and IL-6 and markedly greater amounts of MCP-1 compared to wild-type and H1RKO mice. Because MCP-1 is known to inhibit IL-12 production, the failure of H2RKO mice to generate encephalitogenic Th1 effector cell responses is consistent with inhibition of negative regulation of MCP-1 secretion by H2R signaling in APCs.

Asthma as a paradigm for autoimmune disease

Allergy and autoimmunity result from dysregulation of the immune system. Until recently, it was generally accepted that the mechanisms that govern these disease processes are quite disparate; however, new discoveries suggest possible common pathogenetic effector pathways. This review illustrates the concomitant presentation of these conditions and the potential relationship or common mechanisms in some cases, by looking at the key elements that regulate the immune response in both asthma and autoimmune conditions: mast cells, antibodies, T cells, cytokines, and genetic determinants. The parallel appearance of asthma and autoimmune conditions in the same patients may reveal that such aberrations of the immune system have a common pathophysiologic mechanism. Mast cells, which play a key role in asthma, and the wealth of inflammatory mediators they express, make it likely that they have profound effects on many autoimmune processes. Activation of protein kinases by inflammatory cytokines and environmental stresses may contribute to both allergic and autoimmune diseases. The presence of autoantibodies in some allergic diseases suggests an autoimmune basis for these conditions. Because of the central role T cells play in immune reactivity, the T cell receptor loci have long been considered important candidates for a common disease susceptibility within the immune system such as asthma, atopy, and autoimmunity. Immunomodulation is the key to successful treatment of asthma and autoimmune conditions.

Mast cell-derived tumor necrosis factor induces hypertrophy of draining lymph nodes during infection

Palpable swelling of regional lymph nodes is a common sequela of microbial infections but the mechanism responsible for the sequestration and subsequent coordination of lymphocyte responses within these dynamic structures remains poorly understood. Here we show that draining lymph nodes of mast cell-deficient mice did not demonstrate swelling after intradermal bacterial challenge. Testing of individual mast cell-derived products in this model indicated that tumor necrosis factor was the main mediator of nodal hypertrophy, whereas tryptase and histamine had no effect. After peripheral mast cell activation, both tumor necrosis factor concentrations and the recruitment of circulating T cells were increased within draining nodes. These results show a critical function for peripheral mast cell-derived tumor necrosis factor in regulating the hypertrophy of draining lymph nodes during infection.

Mast Cells Exert Effects Outside the Central Nervous System to Influence Experimental Allergic Encephalomyelitis Disease Course

Previous studies using mast cell-deficient mice (W/W(v)) revealed that mast cells influence disease onset and severity of experimental allergic/autoimmune encephalomyelitis (EAE), the murine model for multiple sclerosis. The mast cell populations of these mice can be restored by transferring bone marrow-derived mast cells (BMMCs). Studies using the W/W(v) reconstitution model have lead to major advances in our understanding of mast cell roles in vivo. However, despite its common use, details regarding the sites and kinetics of mast cell repopulation have remained largely uncharacterized. In this study, we examined the kinetics and tissue distribution of green fluorescent protein(+) BMMCs in reconstituted W/W(v) mice to identify sites of mast cell influence in EAE. Reconstitution of naive animals with BMMCs does not restore mast cell populations to all organs, notably the brain, spinal cord, lymph nodes, and heart. Despite the absence of mast cells in the CNS, reconstituted mice exhibit an EAE disease course equivalent to that induced in wild-type mice. Mast cells are found adjacent to T cell-rich areas of the spleen and can migrate to the draining lymph node after disease induction. These data reveal that mast cells can act outside the CNS to influence EAE, perhaps by affecting the function of autoreactive lymphocytes.

Effect of mast cell in pathogenesis of gastric eosinophilic granuloma

AIM

To investigate the function of mast cells in the pathogenesis of gastric eosinophilic granuloma.

METHODS

Paraffin embedded tissue sections from 23 gastric eosinophilic granuloma patients and 15 gastric ulcer patients were stained with anti-human mast cell tryptase to count the mast cells and degranulated mast cells. Anti-human CD34 antibody was used to detect the mocrovessel density with immunohistochemical technique. Mast cell degranulation was also studied by electron microscope.

RESULTS

The quantity of mast cells in gastric eosinophilic granuloma was similar to that in gastric ulcer(9.1±3.0 vs 8.9±3.0, P>0.05). The quantity and ratio of degranulated mast cells were significantly greater in gastric eosinophilic granuloma patients than in gastric ulcer control subjects(7.3±2.4 vs 4.3±1.4, 80.3±15.7% vs 48.4±15.7%, P<0.01). Microvessel density was higher in the patients of high mast cell count than in patients of low mast cell count (57.3±10.7 vs 32.4±7.2, P<0.01). There was a positive relevance between the amount of mast cells and eosinophils (r = 0.931, P<0.01).

CONCLUSION

Mast cells are important cells in the pathogenesis of gastric eosinophilic granuloma.

Immunoglobulin free light chains and mast cells: pivotal role in T-cell-mediated immune reactions?

Immunoglobulin (Ig) free light (L)-chains have long been considered as the meaningless remnants of a spillover in the regular Ig production by B cells. The recently discovered role for Ig free L-chains in mediating hypersensitivity-like responses sheds new light on their potential role in immune responses. Ig free L-chains can sensitize mast cells, such that a second encounter with the appropriate antigen results in mast-cell activation. The possible importance of this reaction for the induction of T-cell-mediated immune reactions, leading to contact sensitivity, multiple sclerosis and rheumatoid arthritis is discussed.