MEDIATORS OF ACUTE INFLAMMATION AND THEIR ROLES IN MODULATING IN VI3^ LEUKOCYTE INFILTRATION AND PATHOBIOLOGIC ACTIVITY IN THE CONJUNCTIVA
Several substances alter leukocyte motility, but the relative importance of these putative meditors during acute inflammation remains unclear. The present study investigated the roles of several candidate mediators within the context of Type I allergic conjunctival leukocyte infiltration and pathobiologic activity in the guinea pig. Histamine and the leukotrienes (LTs) were found to be the likely important primary mediators of leukocyte emigration into conjunctival tissues. The prostaglandins (PGs) and platelet-activating factor (PAF) tailed to elicit pronounced conjunctival leukocyte infiltration, and leukocytes did not respond to any of the forms of the eosinophil chemotactic factor of anaphylaxis (ECF-A) or bradykinin (BK). Histamine elicited a dose-dependent conjunctival infiltrate which was pre-dominantly eosinophilic. Peak emigration occurred at six hours after treatment, at which time significant damage to the conjunctival epithelium and depletion of goblet cell numbers was correlated with the presence of degranulated and fragmenting eosinophils. In animals presensitized to ovalbumin, antigen challenge evoked extensive accumulations of degranulated and fragmenting eosinophils concurrent with exfoliation and pitting of the epithelium and goblet cell expulsion. Neither pyrilamine nor cimetidine alone produced an inhibitory effect or prevented tissue damage but a combination of these antagonists resulted in a significant reduction of eosinophil numbers and also prevented epithelial damage and depletion of goblet cells associated with Type I allergy. The peptide-containing LTs, LTD4 and LTE4, elicited dose-dependent and exclusively eosinophilic conjunctival infiltrates. Infiltrating eosinophils appeared intact and no instances of epithelial damage were ever observed in LT-treated tissues. LTB4 proved to be less potent in causing cellular infiltration, into the conjunctiva. The slow-reacting substance of anaphylaxis (SRS-A) antagonist, FPL 55712, and the potent and selective peptide-LT antagonist, SK&F 104353, abolished conjunctival eosinophil emigration induced by the peptide-LTs, whereas the cyclooxygenase inhibitor, indomethacin, had no effect. SK&F 104353 alone was ineffective in suppressing leukocyte ingress evoked by topical antigen challenge in presensitized animals, but resulted in a substantial reduction of the response when co-administed with a ovri1 amine-cimetidine combination. A synergistic interaction between LTB4 and LTD4 was also discovered in which the nature and condition of the conjunctival leukocyte infiltrate could be altered by changing the relative concentrations of the substituent LTs. The lack of eosinophil degranulation in response to topical LT treatment was confirmed at the ultrastructural level by electron microscopy, and treatment with histamine, a LT combination or antigen resulted in distinct intracellular changes that were largely confined to eosinophils that had achieved the conjunctival epithelium. In tissues treated with the LT combination or challenged with antigen, numerous close associations between eosinophils and lymphocytes were observed in or immediatly below the conjunctival epithelium. The ultrastructural characteristics noted in the eosinophil cytoplasm distal to these cell-cell appositions were similar to those of fragmented eosinophils seen in areas of heavily damaged conjunctival epithelium. Isolated human eosinophils and neutrophils were shown to possess differential sensitivities to LTB4 and LTD4 by a modified under-agarose chemotaxis assay and a novel sampling method employing digital imaging techniques. The specific eosinophil response to LTD4 was totally suppressed by SK&F 104353, demonstrating that a petide-LT can elicit directional emigration in human leukocytes, and that the response in human eosinophils can be induced by physiologically relevant concentrations of LTD4. These findings indicate that concurrent blockade of histamine- and peptide-LT-receptors may form the basis of a highly effective therapeutic strategy in the all-eviation of several pathobiologic events that characterize a number of clinically important conditions. Moreover, a basis for the selective localization and subsequent activity of the eosinophil in the conjunctival epithelium has also been suggested, which could result in research efforts that may be of broad significance in the clinic.
Networked Digital Library of Theses and Dissertations