Figure 4.

(A) Expression of histamine H₄ receptor mRNA in lavaged peritoneal cells from naïve BALB/c, wild-type WBB6F1/J-Kit^Wand mast cell-deficient WBB6F1/J-Kit^W/Kit^W-v (W/W^v) mice. Levels of mRNA were determined as described in the Methods and normalized to glyceraldehyde-3-phosphate dehydrogenase (GAPDH) levels for each mRNA sample. Data represent the mean ± SEM for n= 5 animals for each group. (B) Effect of histamine receptor subtype antagonists on zymosan-induced neutrophil influx in BALB/c mice. Animals were given the drugs [H₁ antagonists, loratadine and terfenadine (30 mg·kg⁻¹ p.o.); H₂ antagonist, cimetidine (30 mg·kg⁻¹ p.o.); H₃ antagonist, ABT-239 (10 mg·kg⁻¹ i.p.); H₄ antagonist, JNJ7777120 (30 mg·kg⁻¹ s.c.) and dexamethasone (10 mg·kg⁻¹ p.o.)] 30 min prior to zymosan (2 mg per animal). Lavage fluid was collected 4 h later and myeloperoxidase (MPO) activity measured as described in the Methods. Data represent the mean ± SEM of the per cent control MPO activity for five to six animals for each group.