Mechanisms of asthma and allergic inflammation
Histamine downregulates monocyte CCL2 production through the histamine H4 receptor

https://doi.org/10.1016/j.jaci.2007.03.024Get rights and content

Background

The expression of the recently cloned histamine H4 receptor (H4R) by leukocytes suggests a role in immunomodulation.

Objective

The expression and function of the H4R on human monocytes obtained from peripheral blood was investigated.

Methods

H4R expression was studied by using flow cytometry. Effects of H4R stimulation on Ca2+ mobilization was determined fluorometrically, CCL2 production was determined by means of ELISA, intracellular CCL2 staining was measured with flow cytometry, and CCL2 mRNA was measured by using real-time quantitative LightCycler PCR. The relevance of CCL2 production was determined in chemotaxis transmigration assays.

Results

H4R protein was expressed by monocytes and upregulated by IFN-γ. H4R agonists (clobenpropit and 4-methylhistamine) induce a Ca2+ mobilization in monocytes, which could be blocked with the selective H4R antagonist JNJ7777120. Furthermore, H4R agonists downregulated CCL2 protein production. This effect could also be blocked by JNJ7777120. Supernatants of H4R agonist–stimulated monocytes attracted less monocytes in transmigration assays. The downregulation of CCL2 production was regulated at different levels. First, the synthesis of CCL2 mRNA was significantly decreased. Second, intracellular staining suggested an inhibition of CCL2 secretion after stimulation with H4R agonists.

Conclusion

Human monocytes express the H4R, and its stimulation leads to a Ca2+ influx and an inhibition of CCL2 production, resulting in a reduction of monocyte recruitment.

Clinical implications

The H4R could represent an important anti-inflammatory receptor on monocytes and could be an interesting target for drug development.

Section snippets

Monocyte enrichment and isolation

Buffy coats from anonymous healthy blood donors obtained from the local blood bank were used. The buffy coats were disposed of by the blood bank after thrombocyte preparation. Total IgE levels, as well as levels IgE against common aeroallergens (sx-1 screening test), were measured (CAP System; Pharmacia, Freiburg, Germany) and were less than the normal limits of 100 kU/L and 0.35 kU/L, respectively. In case of increased IgE levels, the patient was excluded from the study. Human PBMCs were

Expression of the H4R in monocytes

Monocytes have been shown to express the H4R at the mRNA level, as described by us13 and others.6 Here we showed H4R protein expression on monocytes by means of flow cytometry after staining with a selective H4R antibody directed against the C-terminal tail.25 The specificity of the immunoreactivity was controlled by blocking the staining of the H4R antibody with the respective peptide used to generate the antibody (Fig 1, A).

Upregulation of H4R expression by IFN-γ

The regulation of H4R protein expression was investigated after

Discussion

Previously, it has been shown that the H4R has important immunomodulatory effects on human T lymphocytes14, 29 and human DCs13 in vitro. In a recent investigation using a murine model of allergic airway inflammation, an immunomodulatory role for the H4R was also shown in vivo. H4R knockout mice and mice treated with the H4R inhibitor JNJ7777120 had decreased T-lymphocyte function, which was attributed to a decreased cytokine and chemokine production by DCs.15 The monocyte cell fraction that

References (32)

  • T. Nguyen et al.

    Discovery of a novel member of the histamine receptor family

    Mol Pharmacol

    (2001)
  • Y. Zhu et al.

    Cloning, expression, and pharmacological characterization of a novel human histamine receptor

    Mol Pharmacol

    (2001)
  • C.L. Hofstra et al.

    Histamine H4 receptor mediates chemotaxis and calcium mobilization of mast cells

    J Pharmacol Exp Ther

    (2003)
  • T. Nakayama et al.

    Liver-expressed chemokine/CC chemokine ligand 16 attracts eosinophils by interacting with histamine H4 receptor

    J Immunol

    (2004)
  • P. Ling et al.

    Histamine H4 receptor mediates eosinophil chemotaxis with cell shape change and adhesion molecule upregulation

    Br J Pharmacol

    (2004)
  • K. Takeshita et al.

    Critical role of histamine H4 receptor in leukotriene B4 production and mast cell-dependent neutrophil recruitment induced by zymosan in vivo

    J Pharmacol Exp Ther

    (2003)
  • Cited by (0)

    Supported by grants from the Deutsche Forschungsgemeinschaft (DFG Gu434/5-1) and SFB 566A6 and Wellcome Trust (United Kingdom).

    Disclosure of potential conflict of interest: The authors have declared that they have no conflict of interest.

    View full text