In vitro effects of cetirizine and histamine on human neutrophil function.

IgE-mediated hypersensitivity reactions are characterized by an immediate or early-phase response within the first 30 minutes of exposure to allergen, followed by a late-phase response that begins two to six hours later. Histamine is released during both the early- and late-phase responses and inhibits a variety of neutrophil functions, including superoxide anion generation, chemotaxis, and enzyme secretion. There is some debate as to whether histamine's action on neutrophils is mediated through H1 or H2 receptors, or through a single receptor that recognizes both H1 and H2 agonists. In an effort to understand the mechanism of action of the H1-antagonist cetirizine, we studied its effects on a variety of neutrophil functions. We found that at concentrations up to 35 micrograms/mL), it does not affect superoxide anion production or degranulation. However, at higher concentrations (greater than 35 micrograms/mL), a concentration-dependent inhibition of superoxide anion production is observed. This inhibition is most apparent with responses stimulated by chemotactic factors. Limited inhibition of degranulation and chemotaxis is also seen at high concentrations, but at a level far below that seen with superoxide anion production. These studies indicate that neutrophil function is not altered by the circulating concentrations of cetirizine attained during therapy (less than 10 micrograms/mL), but may be suppressed at higher concentrations. Additional effects of cetirizine on neutrophil function, possible influences of the drug on the inflammatory response, and histamine's modulation of neutrophil function are discussed.