main product of mast cells plays critical role in the pathogenetic pathways of
both allergic rhinitis and asthma. The novel concept of the unique airway
diseases its only supported by the similarities within pathogenetic process.
Antagonists of H1 and H2 receptors are quite effective in allergic rhinitis,
but not effective enough in asthma. In an era of corticosteroids, leucotriene
antagonists and Anti-IgE treatment, there is still a challenge to search for
more effective, more acurate and more safe treatment option. Antagonists
(inversive agonists) of histamine receptors H4 seems to be one of the promising
targets in the allergic rhinitis and asthma treatment. The first H4 antagonist
entered to clinics and the results from a proof-of-concept Phase II clinical
study is expected to be disclosed soon. This review article summarizes
current knowledge on H4R that have been collected in various studies sharing
evidences about efficacy of H4R as a reasonable target for diseases with
histamine involved pathogenetic pathways.