Dynamics of PAF-induced conjunctivitis reveals differential expression of PAF receptor by macrophages and eosinophils in the rat.

The action of platelet-activating factor (PAF) toward the PAF receptor (PAF-R) plays an important role in inflammation. We employed immunohistochemistry and quantitative confocal immunofluorescence microscopy to examine the dynamic changes of PAF-R expression in the conjunctiva in response to PAF-induced conjunctivitis in Brown Norway rats within the first 2 h after topical administration of PAF. Instillation of PAF caused an alteration in pattern of recruitment of macrophages and eosinophils into the conjunctiva, as was visualized by immunohistochemical staining for the antigens ED 1 and ED 2 (markers of macrophages) and MBP (a marker of eosinophils). An increase in the number of PAF-R positive cells was alos detected. Quantitative colocalization analysis revealed ther strongest rise in the degree of PAF-R expression by macrophages within the first 6 h, whereas their infiltration increased throughout the period of observation. However, eosinophils showed a high degree of PAF-R expression during all 24 h of the experiment, although they infiltrated strongly only within the first 2 h. Thus, for the first time, the use of quantitative colocalization analysis software developed by us has reveal intrinsic details of the interaction of PAF anf PAF-R in conjunctivitis, findings not otherwise obtainable by using qualitative approaches alone. Our results provide a theoretical basis for a definition of the proper time-frame in which to prevent and control the infiltration of macrophages and eosinophils into the conjunctiva.