Kinetic studies of galectin-10 release from eosinophils exposed to proliferating T cells

Abstract

Summary Galectin-10 is involved in the T cell suppressive activity of regulatory T cells and eosinophils alike. We have identified a subpopulation of T cell suppressive eosinophils that express CD16 on the surface and contain more galectin-10 compared with conventional CD16-negative eosinophils. Our main goal was to determine how the intracellular protein galectin-10 is released from eosinophils when exposed to proliferating T cells and if such release could be inhibited. Confocal microscopy and imaging flow cytometry were used to study the release of galectin-10 from eosinophils incubated with polyclonally activated T cells. T cell proliferation was monitored by measurement of the incorporation of [3H]-thymidine. Initially, galectin-10-containing synapses formed between eosinophils and T cells. Subsequently, the plasma membrane of eosinophils began to disintegrate and cap-like accumulations of galectin-10 budded on the eosinophil cell surface. Lastly, eosinophil extracellular traps composed of nuclear DNA and galectin-10 were freed. It was solely the CD16-expressing suppressive eosinophils that formed synapses and eosinophil extracellular traps containing galectin-10. Dissolution of the extracellular traps by DNase I partly abrogated the T cell suppression exerted by eosinophils. Extracellular trap formation has mainly been associated with anti-bacterial defense, but we show a new putative function of these cellular formations, as mediators of T cell suppression by enabling the release of galectin-10 from eosinophils.

Charcot–Leyden crystals and other protein crystals driving type 2 immunity and allergy

“…The administration of CLCs together with innocuous antigen, that is, ovalbumin, was able to boost the antigen-specific T cell response in mice which was associated with increased antigen-specific antibody responses [17 ]. High levels of galectin-10 coming from a subset of CD16 + human eosinophils may also have a role in suppression of proliferating T cells [22].…”

“…However, in its soluble form, galectin-10 plays important roles in eosinophil development [8] and it is conceivable that extracellular soluble protein may have as yet undescribed roles. One report demonstrated the presentation of galectin-10 on EETs to suppress Th2 cells [22] and galectin-10 bound to secreted vesicles may be taken up by other cells to initiate cell activation.…”

Platelet association with leukocytes in active eosinophilic esophagitis

“…Yet another potential limitation is that anti-CD16 was used in gating of eosinophils to exclude neutrophils, which express a high level of CD16. Although this is a standard gating method and eosinophils in general do not express CD16 [33,34], CD16 may be induced on a subset of eosinophils in vitro by various mediators or detected on a subset of eosinophils in allergic rhinitis or asthma or even healthy subjects, according to some reports but not others [33][34][35][36][37][38][39][40]. We cannot rule out that a small proportion of eosinophils was gated out in our subjects.…”

Recent advances in understanding the role of eosinophils

“…In one such study, Lingblom et al demonstrated greater suppression of T-cell proliferation by CD16 hi eosinophils from healthy donors compared with CD16 lo eosinophils from the same donors 105 . This suppression was at least partly dependent on galectin-10 (Gal-10) released in extracellular DNA traps when eosinophils come into contact with activated T cells 111 . An area of ongoing controversy, especially in humans, is whether there are developmentally distinct populations of eosinophils that maintain their phenotype and function irrespective of their environment or whether the observed heterogeneity is entirely due to plasticity in response to external cues.…”