The Leukocyte Activation Receptor CD69 Controls T Cell Differentiation through Its Interaction with Galectin-1

Abstract

f CD69 is involved in immune cell homeostasis, regulating the T cell-mediated immune response through the control of Th17 cell differentiation. However, natural ligands for CD69 have not yet been described. Using recombinant fusion proteins containing the extracellular domain of CD69, we have detected the presence of a ligand(s) for CD69 on human dendritic cells (DCs). Pulldown followed by mass spectrometry analyses of CD69-binding moieties on DCs identified galectin-1 as a CD69 counterreceptor. Surface plasmon resonance and anti-CD69 blocking analyses demonstrated a direct and specific interaction between CD69 and galectin-1 that was carbohydrate dependent. Functional assays with both human and mouse T cells demonstrated the role of CD69 in the negative effect of galectin-1 on Th17 differentiation. Our findings identify CD69 and galectin-1 to be a novel regulatory receptor-ligand pair that modulates Th17 effector cell differentiation and function. C D69, a C-type lectin, is a member of the natural killer (NK) receptor family and is induced early following activation of leukocytes (1). The physiological role of this receptor, which is persistently expressed by infiltrating leukocytes in different chronic inflammatory diseases, has been studied in CD69-deficient mice in multiple different models of chronic inflammation (2-5). Thus, we have previously described that CD69 Ϫ/Ϫ mice develop an exacerbated form of collagen-induced arthritis (CIA) (3), a Th1 and Th17 cell-mediated autoimmune condition. Moreover, in an experimental model of autoimmune myocarditis (EAM), CD69 negatively regulates cardiac inflammation through the regulation of heart-specific Th17 responses (4). In this regard, we have detected that CD69 modulates the in vitro differentiation of T cells toward the Th17 lineage through the activation of the Jak3/Stat5 inhibitory pathway (5). On the other hand, CD69 negatively regulates the chemotactic responses of effector lymphocytes and dendritic cells (DCs) to sphingosine 1 phosphate (S1P); CD69 can associate with S1P1 in the cell membrane and induce a conformation of S1P1 that favors its internalization and degradation (6-8). It is clear that the identification of cellular ligands for CD69 is a critical next step to better understand the physiological role of this receptor.Galectins are characterized by a common structural fold and a conserved carbohydrate recognition domain (CRD) with a high affinity for beta-galactosides (9). Despite being soluble proteins, galectins are also expressed on the cell surface due to their association with membrane glycoproteins. Thus, galectin-1 (Gal-1) is expressed by most activated but not resting T and B cells, and it is significantly upregulated in activated macrophages and T regulatory lymphocytes (10). In addition, tolerogenic DCs show a high expression of Gal-1 (11), which is rapidly downregulated in response to maturation signals. Furthermore, Gal-1-deficient DCs show a greater immunogenic potential and an impaired ability to halt the inflammatory phenomenon in a ...

Glycosylation‐dependent interaction between CD69 and S100A8/S100A9 complex is required for regulatory T‐cell differentiation

“…More recently, the DC‐derived galectin‐1 ligand was shown to negatively regulate T helper (T h )17 effector cell differentiation via CD69 (24), whereas the positive expression of CD69 in Foxp3 + T reg cells was shown to maintain immune tolerance (8). However, the role of CD69 in the switch of CD4 + naive T cells into CD25 + Foxp3 + T reg cells has yet to be elucidated.…”

Clinical-Grade Human Multipotent Adult Progenitor Cells Block CD8+ Cytotoxic T Lymphocytes

“…6D). Given the fact that galectin‐1, a β‐galactoside‐binding immune‐suppressive protein, has recently been discovered as a ligand for CD69 on DCs [34], the presence of Gal‐1 on MultiStem was also studied. Fluorescence microscopy revealed Gal‐1 expression (Fig.…”

“…Based on the MultiStem‐mediated elevated levels of CD69 in T cells and the presence of its ligand Gal‐1 [34] in MultiStem, Gal‐1/CD69 binding could be an important mechanism of immune modulation by adult stem cells, independent of cytotoxicity suppression. de la Fuente et al already proved inhibition of T h 17 differentiation and function in mice and humans upon CD69 recruitment [34]. In our study, we demonstrated that Gal‐1 signaling did not mediate the inhibitory effect of MultiStem on T‐cell cytotoxicity.…”

Re‐wiring regulatory cell networks in immunity by galectin–glycan interactions

“…In fact, Gal-1-expressing DCs greatly contributed to the resolution of antigen-specific and autoimmune diseases [93]. Although the precise molecular mechanisms involved in this effect still remain to be explored, recent studies identified CD69 as a counter-receptor for DC-derived Gal-1 on T cells, suggesting that a Gal-1-CD69 axis may contribute to DC-mediated suppression of pro-inflammatory T cell responses [98]. Moreover, DC expression of Gal-1 mediates, at least in part, the tolerogenic effects triggered by IL-10 and apoptotic cells [99,100].…”