Conjunctival eosinophil infiltration evoked by histamine and immediate hypersensitivity. Modification by H1- and H2-receptor blockade.

The present histological studies have demonstrated that histamine causes dose-dependent eosinophil infiltration into the conjunctiva. A highly directional movement toward the conjunctival epithelium was observed, and the presence of large numbers of degranulating eosinophils appeared to result in epithelial cell damage and goblet cell discharge. Blockade of H2-receptors by systemic cimetidine pretreatment significantly inhibited the eosinophil infiltration elicited by an intermediate histamine dose, whereas the H1-receptor blockade produced by systemic pyrilamine pretreatment markedly reduced the response to all histamine doses. The pyrilamine-insensitive residual eosinophil infiltrate was not affected by administering a cimetidine-pyrilamine combination. In animals presensitized to ovalbumin, antigen challenge evoked extensive and directional emigration of eosinophils toward the conjunctival epithelium with resultant exfoliation and depletion of goblet cell populations. In conjunctival immediate hypersensitivity, neither cimetidine nor pyrilamine alone produced an inhibitory effect, but a cimetidine-pyrilamine combination caused a significant reduction in the number of infiltrating eosinophils and prevented epithelial damage and goblet cell depletion. These results suggest that histamine may participate in the recruitment of eosinophils during immediate hypersensitivity reactions. The differential effect of pyrilamine on the eosinophil infiltration evoked by histamine or immediate hypersensitivity may, perhaps, reflect the importance of increased microvascular permeability in facilitating eosinophil emigration.