Histamine as an immune modulator in chronic inflammatory responses

The Role of Crosstalk of Immune Cells in Pathogenesis of Chronic Spontaneous Urticaria

Chronic spontaneous urticaria (CSU) is defined as recurrent episodes of spontaneous wheal development and/or angioedema for more than six weeks and at least twice a week. The core link in the pathogenesis of CSU is the activation of mast cells, T cells, eosinophils, and other immune cells infiltrating around the small venules of the lesion. Increased vascular permeability, vasodilatation, and recruitment of inflammatory cells directly depend on mast cell mediators’ release. Complex regulatory systems tightly influence the critical roles of mast cells in the local microenvironment. The bias toward Th2 inflammation and autoantibodies derived from B cells, histamine expressed by basophils, and initiation of the extrinsic coagulation pathway by eosinophils or monocytes exerts powerful modulatory influences on mast cells. Cell-to-cell interactions between mast cells and eosinophils/T cells also are regulators of their function and may involve CSU’s pathomechanism. This review summarizes up-to-date knowledge regarding the crosstalk between mast cells and other immune cells, providing the impetus to develop new research concepts and treatment strategies for CSU.

Siraitia grosvenorii Residual Extract Attenuates Atopic Dermatitis by Regulating Immune Dysfunction and Skin Barrier Abnormality

Atopic dermatitis is a persistent inflammatory skin disorder. Siraitia grosvenorii fruits (monk fruit or nahangwa in Korean, NHG) are used as a natural sweetener and as a traditional medicine for the treatment of asthma and bronchitis. We evaluated the activity of S. grosvenorii residual extract (NHGR) on allergic inflammation of atopic dermatitis in a Dermatophagoides farinae mite antigen extract (DfE)-treated NC/Nga murine model and in vitro. Oral administration of NHGR significantly reduced epidermal hyperplasia and inflammatory cell infiltration in the skin lesions of DfE-induced atopic dermatitis, as well as the dermatitis severity score. NHGR reduced serum immunoglobulin E levels. Splenic concentrations of IFN-γ, interleukin (IL)-4, IL-5, and IL-13 were reduced by NHGR administration. Immunohistofluorescence staining showed that NHGR administration increased the protein levels of claudin-1, SIRT1, and filaggrin in atopic dermatitis skin lesions. In addition, NHGR inhibited the phosphorylation of mitogen-activated protein kinases and decreased filaggrin and chemokine protein expression in TNF-α/IFN-γ-induced human keratinocytes. Moreover, NHGR also inhibited histamine in mast cells. The quantitative analysis of NHGR revealed the presence of grosvenorine, kaempferitrin, and mogrosides. These results demonstrate that NHGR may be an efficient therapeutic agent for the treatment of atopic dermatitis.

Differential expression of histamine receptors in the bladder wall tissues of patients with bladder pain syndrome/interstitial cystitis - significance in the responsiveness to antihistamine treatment and disease symptoms

Background

Activation of mast cells plays an important role in the pathogenesis of bladder pain syndrome/interstitial cystitis (BPS/IC). Histamine, a mast cell-derived mediators, induced inflammation and hypersensitivity of the bladder. The present study investigated the expressions of histamine receptors in the bladder wall tissues of patients with BPS/IC, and its association with the effectiveness of antihistamine therapy and disease symptoms.

Methods

Bladder tissues were collected from 69 BPS/IC patients and 10 control female patients. The expression of H3R in BPS/IC was further examined in an independent cohort of 10 female patients with BPS/IC and another 10 age-matched female patients. Immunohistochemistry, Western blotting, and quantitative RT-PCR were performed to quantify the expressions of histamine receptors. Statistical analyses of the correlation of histamine receptor expression with antihistamine therapy outcome and severity of disease symptoms were also performed.

Results

The expression of four histamine receptors was significantly elevated in BPS/IC (H1R, P < 0.001; H2R, P = 0.031; H3R, P = 0.008; H4R, P = 0.048). Western blotting revealed that H3R were significantly reduced in the patients, whereas the mRNA levels of H3R were significantly increased. The patients were further divided into antihistamine responders (n = 38) and nonresponders (n = 22). No significant correlation was found in the expression of histamine receptors between responder and nonresponder groups. However, significant correlations between OLS and H1R (P = 0.003) and H3R (P = 0.045) were found.

Conclusion

The present study showed that expression of all the 4 histamine receptors were elevated in BPS/IC. There were no statistical significant correlations between the expression levels of the four different histamine receptors and the treatment outcome of antihistamine therapy (amtitriptyline or cimetidine).

The Role of Histamine and Histamine Receptors in Mast Cell-Mediated Allergy and Inflammation: The Hunt for New Therapeutic Targets

Histamine and its receptors (H1R–H4R) play a crucial and significant role in the development of various allergic diseases. Mast cells are multifunctional bone marrow-derived tissue-dwelling cells that are the major producer of histamine in the body. H1R are expressed in many cells, including mast cells, and are involved in Type 1 hypersensitivity reactions. H2R are involved in Th1 lymphocyte cytokine production. H3R are mainly involved in blood–brain barrier function. H4R are highly expressed on mast cells where their stimulation exacerbates histamine and cytokine generation. Both H1R and H4R have important roles in the progression and modulation of histamine-mediated allergic diseases. Antihistamines that target H1R alone are not entirely effective in the treatment of acute pruritus, atopic dermatitis, allergic asthma, and other allergic diseases. However, antagonists that target H4R have shown promising effects in preclinical and clinical studies in the treatment of several allergic diseases. In the present review, we examine the accumulating evidence suggesting novel therapeutic approaches that explore both H1R and H4R as therapeutic targets for histamine-mediated allergic diseases.

Silencing of H4R inhibits the production of IL-1β through SAPK/JNK signaling in human mast cells

CONTEXT

Mast cell (MC) activation through H4R releases various inflammatory mediators which are associated with allergic asthma.

OBJECTIVES

To investigate the siRNA-mediated gene silencing effect of H4R on human mast cells (HMCs) functions and the activation of stress-activated protein kinases (SAPK)/jun amino-terminal kinases (JNK) signaling pathways for the release of ineterleukin-1β (IL-1β) in HMCs.

MATERIALS AND METHODS

H4R expression was analyzed by RT-PCR and western blotting in human mast cell line-1 (HMC-1) cells and H4RsiRNA transfected cells. The effect of H4RsiRNA and H4R-antagonist on H4R mediated MC functions such as intracellular Ca²⁺ release, degranulation, IL-6 and IL-1β release, and the activation SAPK/JNK signaling pathways were studied. HMC-1 cells were stimulated with 10 μM of histamine (His) and 4-methylhistamine (4-MH) and pretreated individually with H4R-antagonist JNJ7777120 (JNJ), histamine H1 receptor (H1R)-antagonist mepyramine, and signaling molecule inhibitors SP600125 (SP) and Bay117082.

RESULTS

We found that the HMC-1 cells expressed H4R and H4RsiRNA treatment down regulated the H4R expression in HMC-1 cells. Both His and 4-MH induced the intracellular Ca²⁺ release and degranulation whereas; H4R siRNA and JNJ inhibited the effect. Furthermore, the activation of H4R caused the phosphorylation of SAPK/JNK pathways. H4R gene silencing and pretreatment with SP and JNJ decreased His and 4-MH induced phosphorylation of SAPK/JNK. We found that the activation of H4R caused the release of IL-1β (124.22 pg/ml) and IL-6 (122.50 pg/ml) on HMC-1 cells. Whereas, SAPK/JNK inhibitor (68.36 pg/ml) inhibited the H4R mediated IL-1β release.

CONCLUSIONS

Taken together, the silencing of H4R inhibited the H4R mediated MC functions and SAPK/JNK phosphorylation. Furthermore, the H4R activation utilized SAPK/JNK signaling pathway for IL-1β release in HMC-1 cells.

Histamine 1 Receptor Blockade Enhances Eosinophil-Mediated Clearance of Adult Filarial Worms

Filariae are tissue-invasive nematodes that cause diseases such as elephantiasis and river blindness. The goal of this study was to characterize the role of histamine during Litomosoides sigmodontis infection of BALB/c mice, a murine model of filariasis. Time course studies demonstrated that while expression of histidine decarboxylase mRNA increases throughout 12 weeks of infection, serum levels of histamine exhibit two peaks—one 30 minutes after primary infection and one 8 weeks later. Interestingly, mice treated with fexofenadine, a histamine receptor 1 inhibitor, demonstrated significantly reduced worm burden in infected mice compared to untreated infected controls. Although fexofenadine-treated mice had decreased antigen-specific IgE levels as well as lower splenocyte IL-5 and IFNγ production, they exhibited a greater than fourfold rise in eosinophil numbers at the tissue site where adult L. sigmodontis worms reside. Fexofenadine-mediated clearance of L. sigmodontis worms was dependent on host eosinophils, as fexofenadine did not decrease worm burdens in eosinophil-deficient dblGATA mice. These findings suggest that histamine release induced by tissue invasive helminths may aid parasite survival by diminishing eosinophilic responses. Further, these results raise the possibility that combining H1 receptor inhibitors with current anthelmintics may improve treatment efficacy for filariae and other tissue-invasive helminths.

Filariae are tissue-invasive parasitic roundworms that infect over 100 million people worldwide and cause debilitating conditions such as river blindness and elephantiasis. One of the major factors limiting our ability to eliminate these infections is the lack of drugs that kill adult worms when given as a short course therapy. Additionally, the mechanisms by which adult worms are cleared from infected individuals remains poorly understood. In this study, we demonstrate that treatment of infected mice with fexofenadine, an inhibitor of histamine receptor 1, significantly reduces adult worm numbers through a mechanism dependent on host eosinophils. These findings suggest that histamine release induced by parasitic worms may aid parasite survival by decreasing eosinophilic responses. Further, as antihistamines are generally safe medications, these results raise the possibility that antihistamine therapy may be useful either alone, or potentially in combination with other antifilarial medications such as diethylcarbamazine (DEC), to eliminate adult filarial worms from infected individuals.

Histamine induces the neuronal hypertrophy and increases the mast cell density in gastrointestinal tract

Histamine is an endogenous biogenic amine that is synthesized from the basic amino acid histidine. Ability to mimic anaphylaxis is one of the first described functions of histamine and it has been demonstrated that histamine plays a significant role in the regulation of immune system and neuronal function, influences neuronal morphology and is involved in mast cells (MCs) chemotaxis. MCs as histamine releasers, may thus also interact with neuronal function. In the present study, we aimed to evaluate the role of histamine on mast cell density and neuronal morphology in the gastrointestinal tract of the mouse. Ten mice were daily injected intraperitoneally for 7 days with 20 mg/kg of histamine diluted in 0.5 ml physiological serum. After 7 days, mice were euthanised and samples from stomach, small bowel, colon and appendix were processed for histological examination. Immunohistochemistry was performed employing primary antibodies directed against triptase for mast cells and PGP 9.5 antigen for neuronal structures. The density of triptase and PGP 9.5 positive cells and the morphology of the ganglia were quantitatively evaluated by digital image analysis. The number of ganglia was higher in stomach, small bowel, colon and appendices of the histamine group when compared with the control group. Only in appendices and colon, the number of Schwann cells was significantly higher than that of the control group. The PGP 9.5 expression and the mean area of ganglia showed a significant increase only in appendices. In histamine group the MCs were clustered especially in the lamina propria. Mast cell density (MCD) was significantly higher than the control group in the small bowel, colon and appendices tissues. The intraperitoneally injection histamine increases the MCD and induces the neuronal hypertrophy and after the comparison of the organs in the gastrointestinal tract the results indicated the most effected organ as the appendices.

Involvement of histamine receptors in SAPK/JNK phosphorylation

Histamine is a mediator of inflammation in allergic disease and asthma. Stress activated protein kinases/c-jun N-terminal kinases (SAPK/JNK) are involved in asthma. This study examined the role of histamine receptors on the phosphorylation of SAPK/JNK in splenocytes. C57BL/6 mice splenocytes were treated with histamine (10⁻⁴ M to 10⁻¹¹ M), and its selective receptor agonists, phorbol 12 myristate 13-acetate (PMA) was used as a positive control, and phosphorylation of SAPK/JNK was determined. Histamine (10⁻⁴ M-10⁻⁸ M) inhibited phosphorylation of SAPK/JNK. H1R agonist betahistine (10⁻⁵ M) decreased SAPK/JNK phosphorylation and H2R agonist amthamine (10⁻⁵ M) did not show any significant effect. However, H3R agonist methimepip (10⁻⁶ M) and H4R agonist 4-methyl histamine (10⁻⁶ M), increased SAPK/JNK phosphorylation. We used TNFα knockout mice to determine if histamine regulated SAPK/JNK phosphorylation via TNFα. While the effects of histamine and H1 agonists were similar to that of wild type mice in inhibiting the phosphorylation of SAPK/JNK, the effects of H3 and H4 agonists differed in TNFα knockout mice splenocytes. Activation of H3 receptors decreased SAPK/JNK phosphorylation in TNFα knockout mice, as opposed to an increase in wild type mice, whereas H4 agonist did not show any significant effect on the phosphorylation of SAPK/JNK. This data showed that histamine acting through H4 receptors caused the phosphorylation of SAPK/JNK via TNFα. The role of H4 receptors in pro-inflammatory response is intriguing.

Regulation of ERK2 phosphorylation by histamine in splenocytes

Histamine is implicated in allergic disease and asthma and ERK1/2 is involved in allergic inflammation including Th2 differentiation and proliferation. This study was designed to study the effects of histamine on ERK1/2 phosphorylation in splenocytes. C57/BL6 splenocytes were treated with different concentrations of histamine (10(-4) to 10(-11) M). Histamine (10(-4) M) increased ERK2 phosphorylation. There was, however, no significant effect seen at other concentrations (10(-11) to 10(-6) M). Surprisingly, H1 receptor agonist β-histine (10(-5) M), H2 agonist amthamine (10(-5) M), H3 agonist methimepip (10(-6) M), and H4 agonist 4-methyl histamine (10(-6) M), all increased ERK2 phosphorylation. H1R antagonist pyrilamine (10(-6) M), H2R antagonist ranitidine (10(-5) M), H3/H4R antagonist thioperamide (10(-6) M), and H3R antagonist clobenpropit (10(-5) M) inhibited histamine-mediated ERK2 phosphorylation suggesting that all four histamine receptor subtypes played some role in this phosphorylation. Because tumor necrosis factor-α (TNF-α) causes phosphorylation of ERK1/2, we investigated whether histamine acted via secretion of TNF-α to affect ERK1/2 phosphorylation. As a consequence, TNF-α knockout mice were used and we found that there was inhibition of ERK1 and ERK2 phosphorylation by H2, H3, and H4 agonists. This was in contrast to the wild-type splenocytes where histamine augmented the phosphorylation of ERK2 via H2, H3, and H4 receptors. In TNF-α knockout mice histamine did not affect the phosphorylation of ERK2 via H1 receptors. The results suggested that histamine indirectly caused the ERK2 phosphorylation via its effects on the secretion of TNF-α and these effects were mediated via H1, H2, H3, and H4 receptors.