Binding of DC-HIL to Dermatophytic Fungi Induces Tyrosine Phosphorylation and Potentiates Antigen Presenting Cell Function

Abstract

APCs express receptors recognizing microbes and regulating immune responses by binding to corresponding ligands on immune cells. Having discovered a novel inhibitory pathway triggered by ligation of DC-HIL on APC to a heparin/heparan sulfate-like saccharide of syndecan-4 on activated T cells, we posited DC-HIL can recognize microbial pathogens in a similar manner. We showed soluble recombinant DC-HIL to bind the dermatophytes Trichophyton rubrum and Microsporum audouinii, but not several bacteria nor Candida albicans. Dermatophyte binding was inhibited completely by the addition of heparin. Because DC-HIL contains an ITAM-like intracellular sequence, we questioned whether its binding to dermatophytes can induce tyrosine phosphorylation in dendritic cells (DC). Culturing DC with T. rubrum (but not with C. albicans pseudohyphae) induced phosphorylation of DC-HIL, but not when the tyrosine residue of the ITAM-like sequence was mutated to phenylalanine. To examine the functional significance of such signaling on DC, we cross-linked DC-HIL with mAb (surrogate ligand), which not only induced tyrosine phosphorylation but also up-regulated expression of 23 genes among 662 genes analyzed by gene-array, including genes for profilin-1, myristoylated alanine rich protein kinase C substrate like-1, C/EBP, LOX-1, IL-1β, and TNF-α. This cross-linking also up-regulated expression of the activation markers CD80/CD86 and heightened APC capacity of DC to activate syngeneic T cells. Our findings support a dual role for DC-HIL: inhibition of adaptive immunity following ligation of syndecan-4 on activated T cells and induction of innate immunity against dermatophytic fungi.

Generation and functional characterization of MDSC-like cells

“…[18][19][20][21][22][23] Using FACS analysis, we found that IL-10-APC in contrast to moDC express higher levels of GITR, GITRL, syndecan-4 and PD-1. Furthermore, we were able to confirm our results obtained from the transcriptome analysis by showing that IL-10-APC express higher levels of osteoactivin, whereas PD-L1 was not upregulated (Fig.…”

“…18,20,21 Osteoactivin differs from other inhibitory molecules since it is not only expressed on lymphoid, but also on non-lymphoid cells such as melanocytes, keratinocytes and osteoblasts and has an intracellular ITAM. [31][32][33] Cross-linking of the osteoactivin receptor with specific antibodies was shown to induce tyrosine phosphorylation of the ITAM 20,22 suggesting that activation of osteoactivin induces MDSC to express IFNg, nitric oxide and reactive oxygen species. 20 Mice lacking the osteoactivin/syndecan-4 pathway are characterized through a massive expansion of pathogenic T cells during experimental autoimmune encephalomyelitis 20 or following allogeneic bone marrow transplantation, an effect that might be mediated through a combination of hyperactive APC and disabled MDSC.…”

Lysosomal Stress in Obese Adipose Tissue Macrophages Contributes to MITF-Dependent Gpnmb Induction

“…These mice exhibit autoimmune pigmentary glaucoma and compromising ocular immunosuppression, which is manifested by deficient anterior chamberassociated immune deviation (18,46). In the context of innate immunity, Gpnmb was demonstrated to be involved in recognition of dermatophytic fungi (24). Overexpression of Gpnmb dampens LPS responses, suggesting that Gpnmb negatively regulates inflammatory macrophage responses (17).…”

“…It is also referred to as osteoactivin, hematopoietic growth factor-inducible neurokinin 1, and the dendritic cell-associated heparin sulfate proteoglycan-dependent integrin ligand (18)(19)(20)(21). Gpnmb has been implicated in regulation of both adaptive and innate immunity (22)(23)(24). Interestingly, Gpnmb induction has also been observed in a mouse model of Gaucher disease, a macrophage lipid-storage disease characterized by deficient lysosomal acid b-glucosidase and IR in humans (25,26).…”

The Arthroderma benhamiae Hydrophobin HypA Mediates Hydrophobicity and Influences Recognition by Human Immune Effector Cells

“…It was shown previously that pathogenic ascomycetes, including dermatophytes, bind to DCs via the C-type lectin DC-SIGN (dendritic cell-specific intercellular adhesion molecule 3-grabbing nonintegrin) (12,30). A novel pattern recognition pathway to detect dermatophytes via binding to DC-HIL (dendritic cell-associated heparan sulfate proteoglycan-integrin ligand) (31) and the subsequent phosphorylation of an ITAM (immunoreceptor tyrosine-based activation motif) was suggested previously (11). Since binding and phosphorylation have been observed for Trichophyton rubrum but not for Candida albicans, it is conceivable that this mechanism is specific to dermatophytes.…”