Histology of ocular late-phase reaction in guinea pigs passively sensitized with IgG1 antibodies.

The ocular late-phase reaction (LPR) is a mast cell-dependent, delayed inflammatory reaction developing 4-12 h after the early-phase reaction (EPR). We developed a passive IgG1 antibody-dependent guinea pig model that clinically reproduced the biphasic reaction of ocular EPR and LPR. An EPR was observed in all animals; a biphasic, multiphasic or prolonged inflammation was observed in the animals maintained for 9 and 24 h. The substantia propria of eyes undergoing EPR (0.5 h) showed intense edema, mast cell degranulation (88%), and 4-fold increase in eosinophils. At 9 h, the neutrophils and eosinophils had increased 11- and 25-fold, respectively. The number of basophils and lymphocytes was significantly increased compared to the controls (p less than 0.05). Of the mast cells, 45% were degranulated compared with 19% for controls. Cellular reactions had subsided by 24 h. Conjunctival epithelium also accumulated inflammatory cells as did the stroma of the lid skin. These histologic changes in ocular tissues undergoing anaphylaxis demonstrated that mast cell degranulation was most severe in the early phase, whereas neutrophil, eosinophil, and basophil accumulation was most marked in the late phase.