Figure 4.

Histamine-induced eosinophil shape change is mediated by the H₄ receptor. (a) Histamine induced eosinophil shape change was blocked by the H₄ receptor antagonist JNJ 7777120, the H₃/H₄ receptor antagonist thioperamide, but not by H₁, H₂ or H₃ receptor antagonists. The H₁, H₂ and H₃ receptor antagonists used in studies were diphenhydramine, ranitidine and JNJ 6379490, respectively. Human PMNL were pretreated with 10 μM of different histamine receptor antagonists, followed by 10-min treatment with 1 μM histamine. Eosinophil shape change was monitored by flow cytometry. The percentage of cell shape change was calculated based on the increase in FSC from those of untreated samples. Data shown are a representative of three repeated experiments. Data are mean±s.d. and n=3. Statistical significance (P-value) was determined by the Student's t-test. (b) Determination of IC₅₀ values of JNJ 7777120, thioperamide and H₃ receptor antagonist on histamine-induced eosinophil shape change. Human PMNL were pretreated with different antagonists for 10 min before inducing cell shape change with 1 μM histamine. Eosinophil shape change was monitored by flow cytometry. The percentage of inhibition was calculated based on the decrease in shape change compared to samples treated with1 μM histamine only. Data shown are a representative of four repeated experiments and each data point is a mean±s.d. and n=3. IC₅₀ values were calculated with the GraphPad Prism program. (c) Concentration-dependent effects of histamine, H₃/H₄ receptor agonist imetit and H₄ receptor agonist clobenpropit on human eosinophil shape change. Data are mean±s.d. and n=3. EC₅₀ values were calculated with the GraphPad Prism program.