H4 receptor

H4 Receptor

The H4 receptor is a type of histamine receptor that is primarily involved in the regulation of immune responses. It is one of the four known histamine receptors, the others being H1, H2, and H3 receptors. The H4 receptor is encoded by the HRH4 gene in humans.

Structure

The H4 receptor is a G protein-coupled receptor (GPCR) that is structurally similar to other histamine receptors. It consists of seven transmembrane domains, an extracellular N-terminus, and an intracellular C-terminus. The receptor is coupled to G proteins that mediate its intracellular signaling pathways.

Expression

The H4 receptor is predominantly expressed in bone marrow and white blood cells, such as eosinophils, basophils, and mast cells. It is also found in the spleen, thymus, and other tissues involved in the immune response.

Function

The primary role of the H4 receptor is in the modulation of immune cell activity. It is involved in:

• Chemotaxis: The H4 receptor mediates the movement of immune cells towards sites of inflammation or injury.
• Cytokine release: Activation of the H4 receptor can lead to the release of various cytokines, which are signaling molecules that modulate immune responses.
• Regulation of mast cell activity: The H4 receptor influences the degranulation of mast cells, which are involved in allergic reactions.

Pharmacology

The H4 receptor is a target for drug development due to its role in immune regulation. Antagonists of the H4 receptor are being investigated for their potential in treating conditions such as asthma, allergic rhinitis, and autoimmune diseases.

Ligands

Several ligands have been identified that interact with the H4 receptor:

• Agonists: These are compounds that activate the H4 receptor. Examples include histamine itself and certain synthetic molecules.
• Antagonists: These are compounds that block the H4 receptor. Examples include JNJ 7777120 and other experimental drugs.

Clinical Significance

The H4 receptor is a promising target for new therapies aimed at treating inflammatory and allergic conditions. Research is ongoing to better understand its role in various diseases and to develop effective H4 receptor modulators.

See Also

• Histamine
• Histamine receptor
• Immune system

References

• Leurs, R., et al. (2009). "The histamine H4 receptor: from molecular model to clinical development." Nature Reviews Drug Discovery, 8(6), 473-490.
• Thurmond, R. L., et al. (2008). "Histamine and histamine receptors: recent progress in histamine research." British Journal of Pharmacology, 154(1), 3-13.