Role of histamine H4 receptor in allergic conjunctivitis in mice

We investigated the character of histamine H1 receptor and H4 receptor in allergic conjunctivitis. Histamine is the most important mediator in allergic conjunctivitis. We measured eye scratching behavior and allergic-like symptoms score, that is, hyperemia and edema in ICR mice, and examined which receptors intimately involved in allergic conjunctivitis. Histamine caused a dose-dependent eye scratching behavior and allergic-like symptoms. Histamine H1 receptor antagonist (levocabastine) and H4 receptor antagonist (JNJ7777120) inhibited eye scratching behavior and histamine H1 receptor antagonist inhibited allergic-like symptoms induced by histamine. Additionally, combination of levocabastine and JNJ7777120 caused more potent inhibition in allergic conjunctivitis. On the other hand, both selective histamine H1 receptor agonist (HTMT) and selective H4 receptor agonist (4-methylhistamine) induced a dose-dependent eye scratching behavior and allergic-like symptoms. JNJ7777120 inhibited the effect of HTMT. However, levocabastine caused no inhibition on the response of 4-methylhistamine. H4 receptor was closely related with allergic conjunctivitis. H4 receptor antagonists may be effective in allergic conjunctivitis which showed no inhibition by histamine H1 receptor antagonists.