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L. Tinios, M. Mroz, P.J. Gomes, M.B. Abelson; Flow Cytometric Analysis of ICAM-1 and HLA-DR Expression in Conjunctival Epithelium Following Allergen Challenge . Invest. Ophthalmol. Vis. Sci. 2003;44(13):3742.
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Purpose: Expression of inflammatory cell-markers has previously been shown to increase in response to allergen challenge. The purpose of this study was to determine what happens to expression after 24-hour re-challenge. Methods: Bilateral conjunctival allergen challenge (CAC) was performed the morning of Visit 1 and again 24-hours later at Visit 2. Each subject was challenged using a dose of allergen previously determined to elicit a positive reaction (defined as moderate or greater itching and redness). Impression cytology specimens were collected from neighboring areas of the superotemporal and inferotemporal bulbar conjunctiva at 4 times during the study- 1 hour prior to CAC at Visit 1 (Pre-V1); 45 minutes post CAC at Visit 1 (V1-Post); 1 hour prior to CAC at Visit 2 (Pre-V2); and 45 minutes post CAC at Visit 2 (V2-Post). Cells were processed for flow cytometry using monoclonal antibodies to ICAM-1 and HLA-DR antigens (Beckman Coulter). Percentages of positive cells were calculated and levels of expression quantified after conversion into standardized units of fluorescence (ABC units). Results: The 9 subjects enrolled all exhibited a successful allergic response to challenge. ICAM-1 expression, both in percentage of positive cells and level of expression, was significantly increased at V1-Post and Pre-V2 compared with Pre-V1 levels. ICAM-1 expression at V2-Post returned to near Pre-V1 levels. Mean percentage of ICAM-1 positive cells was 53% at Pre-V1, 67% at V1-Post (P = 0.045), 74% at Pre-V2 (P = 0.014), and 60% at V2-Post (P = 0.136). Mean level of expression of ICAM-1 was 393 ABCs at Pre-V1, 895 at V1-Post (P = 0.004), 1104 at Pre-V2 (P = 0.017), and 592 at V2-Post (P = 0.381). HLA-DR expression was similar in trend to that of ICAM-1; however, the changes were not statistically significant. Conclusions: As expected, ICAM-1 expression was significantly upregulated after the first challenge. The fact that expression decreased after re-challenge strongly suggests the presence of some sort of negative feedback mechanism, possibly regulated by mediators from cells in the tissue.
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