Short Ragweed Pollen Primes Macrophage Polarization toward an Alternatively Activated Phenotype via TSLP/TSLPR Signaling Pathway in Allergic Conjunctivitis

Abstract

Purpose : The role of macrophage in allergic disease is not well elucidated. This study was to explore a novel phenomenon that short ragweed (SRW) pollen primes macrophage polarization toward an alternatively activated (M2) phenotype that promotes allergic inflammation by producing OX40L, CCL17 and CCL22.

Methods : A murine model of experimental allergic conjunctivitis (EAC) was induced in wild-type BALB/c or TSLP receptor knockout (TSLPR-/-) mice by SRW pollen, with untreated and PBS-treated mice as controls. The eyeballs, conjunctiva, cervical lymph nodes (CLNs), and bone marrow derived macrophages were used for study. Gene expression was determined by RT-qPCR, protein production was evaluated by immunostaining, ELISA and flow cytometry.

Results : Typical allergic manifestations and stimulated TSLP signaling and Th2 hyperresponses were observed in ocular surface of EAC models in BALB/c mice induced by SRW. The mRNA levels of Arginase 1 (Arg1), FIZZ1 and Ym1, the markers for M2 phenotype, were highly expressed by conjunctival tissue and draining CLNs of BALB/c-EAC when compared with control mice. Immunofluorescent staining confirmed the increase of these M2 markers by macrophages in ocular surface and CLNs of BALB/c-EAC mice. The expression of TSLPR and OX40L at mRNA and protein levels by macrophage was detected in conjunctiva and CLNs as evaluated by RT-qPCR, double attaining with macrophage marker F4/80, and flow cytometric analysis. M2 macrophages were found to produce CCL17 and CCL22 in the ocular surface and CLNs. In contrast, EAC model with TSLPR-/- mice did not show allergic signs, did not express higher levels of Th2 cytokines, IL-4, IL-5 and IL-13, neither the M2 markers by macrophages. In vitro cultures model further revealed that SRW pollen extracts stimulate the expression of TSLPR, OX40L, CCL17 and CCL22 by macrophage derived from wild-type BALB/c but not those from TSLPR-/- mice.

Conclusions : These findings demonstrate that short ragweed pollen primes macrophages polarization toward to M2 phenotype via TSLP/TSLPR signaling, and the M2 macrophages enhance allergic inflammation by producing Th2 inducing cytokine OX40L and chemokines CCL17 and CCL22. The findings provide a new insight on allergic pathogenesis and the therapeutic potential to treat allergic diseases.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.