Histamine and its 4 receptors represent a complex system of immunoregulation

Histamine is a biogenic amine with extensive effects on many cell types:

- antigen-presenting cells
- natural killer cells
- epithelial cells
- T and B lymphocytes


Histamine structure. Image source: Wikipedia.

Histamine and its 4 receptors represent a complex system of immunoregulation with effects dependent on receptor subtypes.

H1-antihistamines were introduced for clinical use 70 years ago. H1-antihistamines are inverse agonists (i.e., not antagonists or blockers).

We still do not fully understand the complex regulatory interactions between histamine and the host immune response to everyday microbial and environmental challenges.

Important advances include:

- improved nasal and ophthalmic H1-antihistamines with rapid onset of action (in minutes) for allergic rhinitis and allergic conjunctivitis treatment, respectively

- effective and safe use of high (up to 4-fold) doses of oral second-generation H1-antihistamines for chronic urticaria treatment.

New H1-antihistamines introduced for clinical use include:

- oral formulations (bilastine and rupatadine)
- ophthalmic formulations (alcaftadine and bepotastine)

Clinical studies of H3-antihistamines with enhanced decongestant effects have been conducted in patients with allergic rhinitis.

New compounds being studied include H4-antihistamines with anti-inflammatory effects in allergic rhinitis and atopic dermatitis.

Antihistamines have a storied past and a promising future.

References:

Regulation of the immune response and inflammation by histamine and histamine receptors. Liam O’Mahony, PhD, Mübeccel Akdis, MD, PhD, Cezmi A. Akdis, MD. JACI.

Histamine and H1-antihistamines: Celebrating a century of progress. JACI.