Figure 5.

Histamine-induced adhesion molecule expression on eosinophils is mediated by the H₄ receptor. (a) Cell surface expression of adhesion molecules CD11b/CD18 and CD54 on eosinophils was upregulated by histamine. Human PMNL were treated with different concentrations of histamine or chemokine eotaxin-2 for 10 min at 37°C. Cell samples were fixed with paraformaldehyde and stained with FITC-conjugated antibodies specific for CD11b, CD11a or CD54. Expression of adhesion molecules on eosinophils was monitored by flow cytometry. The percentage of upregulation was calculated based on the increase in expression levels from those of untreated samples. Data are mean±s.d. and n=3. (b) Histamine-induced adhesion molecule upregulation on eosinophils was blocked by the H₄ receptor antagonist JNJ 7777120 and 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 for 10 min, followed by 10-min treatment with 1 μM histamine at 37°C. Cell samples were fixed with paraformaldehyde and stained with FITC-conjugated antibodies specific for CD11b or CD54. Data are mean±s.d. and n=3. Statistical significance (P-value) was determined by the Student's t-test.