CD101 is expressed by skin dendritic cells. Role in T-lymphocyte activation

Pro-inflammatory feedback loops define immune responses to pathogenic Lentivirus infection

BACKGROUND

The Lentivirus human immunodeficiency virus (HIV) causes chronic inflammation and AIDS in humans, with variable rates of disease progression between individuals driven by both host and viral factors. Similarly, simian lentiviruses vary in their pathogenicity based on characteristics of both the host species and the virus strain, yet the immune underpinnings that drive differential Lentivirus pathogenicity remain incompletely understood.

METHODS

We profile immune responses in a unique model of differential lentiviral pathogenicity where pig-tailed macaques are infected with highly genetically similar variants of SIV that differ in virulence. We apply longitudinal single-cell transcriptomics to this cohort, along with single-cell resolution cell-cell communication techniques, to understand the immune mechanisms underlying lentiviral pathogenicity.

RESULTS

Compared to a minimally pathogenic lentiviral variant, infection with a highly pathogenic variant results in a more delayed, broad, and sustained activation of inflammatory pathways, including an extensive global interferon signature. Conversely, individual cells infected with highly pathogenic Lentivirus upregulated fewer interferon-stimulated genes at a lower magnitude, indicating that highly pathogenic Lentivirus has evolved to partially escape from interferon responses. Further, we identify CXCL10 and CXCL16 as important molecular drivers of inflammatory pathways specifically in response to highly pathogenic Lentivirus infection. Immune responses to highly pathogenic Lentivirus infection are characterized by amplifying regulatory circuits of pro-inflammatory cytokines with dense longitudinal connectivity.

CONCLUSIONS

Our work presents a model of lentiviral pathogenicity where failures in early viral control mechanisms lead to delayed, sustained, and amplifying pro-inflammatory circuits, which in turn drives disease progression.

Evidence that Cd101 is an autoimmune diabetes gene in nonobese diabetic mice

We have previously proposed that sequence variation of the CD101 gene between NOD and C57BL/6 mice accounts for the protection from type 1 diabetes (T1D) provided by the insulin-dependent diabetes susceptibility region 10 (Idd10), a <1 Mb region on mouse chromosome 3. In this study, we provide further support for the hypothesis that Cd101 is Idd10 using haplotype and expression analyses of novel Idd10 congenic strains coupled to the development of a CD101 knockout mouse. Susceptibility to T1D was correlated with genotype-dependent CD101 expression on multiple cell subsets, including Foxp3(+) regulatory CD4(+) T cells, CD11c(+) dendritic cells, and Gr1(+) myeloid cells. The correlation of CD101 expression on immune cells from four independent Idd10 haplotypes with the development of T1D supports the identity of Cd101 as Idd10. Because CD101 has been associated with regulatory T and Ag presentation cell functions, our results provide a further link between immune regulation and susceptibility to T1D.

Interacting regions of CD81 and two of its partners, EWI-2 and EWI-2wint, and their effect on hepatitis C virus infection

CD81 is a tetraspanin protein that is involved in several essential cellular functions, as well as in the hepatitis C virus (HCV) infection. CD81 interacts with a high stoichiometry with its partner proteins EWI-2, EWI-2wint, and EWI-F. These latter proteins modify the functions of CD81 and can thereby potentially inhibit infection or modulate cell migration. Here, we characterized the cleavage of EWI-2 leading to the production of EWI-2wint, which has been shown to inhibit HCV infection. We determined the regions of EWI-2/EWI-2wint and CD81 that are important for their interaction and their functionality. More precisely, we identified a glycine zipper motif in the transmembrane domain of EWI-2/EWI-2wint that is essential for the interaction with CD81. In addition, we found that palmitoylation on two juxtamembranous cysteines in the cytosolic tail of EWI-2/EWI-2wint is required for their interaction with CD81 as well as with CD9, another tetraspanin. Thus, we have shown that palmitoylation of a tetraspanin partner protein can influence the interaction with a tetraspanin. We therefore propose that palmitoylation not only of tetraspanins, but also of their partner proteins is important in regulating the composition of complexes in tetraspanin networks. Finally, we identified the regions in CD81 that are necessary for its functionality in HCV entry and we demonstrated that EWI-2wint needs to interact with CD81 to exert its inhibitory effect on HCV infection.

In situ chemical cross-linking on living cells reveals CD9P-1 cis-oligomer at cell surface

Tetraspanins are integral membrane proteins involved in a variety of physiological and pathological processes. They associate with each other in multimolecular complexes containing numerous membrane proteins. As a first step towards the study of the supramolecular organization of tetraspanin complexes, we have implemented a proteomic approach based on in situ protein cross-linking on living cells followed by affinity purification of tetraspanin complexes. This allowed observing the presence of high molecular weight protein complexes that were characterized as containing CD9P-1/CD315 using LC-MS/MS. Western blot analyses and the use of different tags demonstrated the presence of CD9P-1 oligomer in cis-association at cell surface. A significant amount of CD9P-1 oligomer was observed on various cell types. We have shown that CD9P-1 self-associates independently from its association with tetraspanins. However, the expression level of CD9 or CD81 that associate directly and specifically with CD9P-1, positively modulates the cross-linking efficiency of CD9P-1. Thus, tetraspanins can play a role on CD9P-1 oligomerization status.

CD101 Surface Expression Discriminates Potency Among Murine FoxP3+ Regulatory T Cells

CD4+CD25+FoxP3+ regulatory T cells (Treg) have been shown to be protective in animal models of autoimmunity and acute graft-vs-host disease. However, owing to the functional heterogeneity among CD4+CD25+ T cells, surface markers expressed selectively on functionally active Treg would be useful for purposes of identifying and isolating such cells. We generated a rabbit mAb against murine CD101, a transmembrane glycoprotein involved in T cell activation. Among freshly isolated T cells, CD101 was detected on 25-30% of CD4+CD25+ Treg and approximately 20% of conventional memory T cells. CD101(high) Treg displayed greater in vitro suppression of alloantigen-driven T cell proliferation as compared with CD101(low) Treg. In a model of graft-vs-host disease induced by allogeneic bone marrow transplantation in vivo bioluminescence imaging demonstrated reduced expansion of donor-derived luciferase-labeled conventional T cells in mice treated with CD101(high) Treg, compared with CD101(low) Treg. Moreover, treatment with CD101(high) Treg resulted in improved survival, reduced proinflammatory cytokine levels and reduced end organ damage. Among the CD101(high) Treg all of the in vivo suppressor activity was contained within the CD62L(high) subpopulation. We conclude that CD101 expression distinguishes murine Treg with potent suppressor activity.

Evidence for Cd101 but not Fcgr1 as candidate for type 1 diabetes locus, Idd10

Among polygenes conferring susceptibility to type 1 diabetes in the NOD mouse, Idd10 on distal chromosome 3 has been shown to be important for disease susceptibility. In this study, we investigated the candidacy of Fcgr1 and Cd101 for Idd10, by congenic mapping and candidate gene sequencing. Among seven NOD-related strains studied, the IIS mouse was found to possess a recombinant Idd10 interval with the same sequence at Fcgr1 as the NOD mouse, but a different sequence at Cd101 from that in the NOD mouse with 10 amino acid substitutions. The frequency of type 1 diabetes in NOD mice congenic for IIS Idd10 (NOD.IISIdd10) was significantly reduced as compared to that in the NOD mouse, despite the presence of the identical Fcgr1 sequence. These data indicate that IIS mice possess a resistant allele at Idd10, and suggest that Cd101, but not Fcgr1, is responsible for the Idd10 effect.

Identification of a structurally distinct CD101 molecule encoded in the 950-kb Idd10 region of NOD mice

Genes affecting autoimmune type 1 diabetes susceptibility in the nonobese diabetic (NOD) mouse (Idd loci) have been mapped using a congenic strain breeding strategy. In the present study, we used a combination of BAC clone contig construction, polymorphism analysis of DNA from congenic strains, and sequence mining of the human orthologous region to generate an integrated map of the Idd10 region on mouse chromosome 3. We found seven genes and one pseudogene in the 950-kb Idd10 region. Although all seven genes in the interval are Idd10 candidates, we suggest the gene encoding the EWI immunoglobulin subfamily member EWI-101 (Cd101) as the most likely Idd10 candidate because of the previously reported immune-associated properties of the human CD101 molecule. Additional support for the candidacy of Cd101 is the presence of 17 exonic single-nucleotide polymorphisms that differ between the NOD and B6 sequences, 10 causing amino acid substitutions in the predicted CD101 protein. Four of these 10 substitutions are nonconservative, 2 of which could potentially alter N-linked glycosylation. Considering our results together with those previous reports that antibodies recognizing human CD101 modulate human T-cell and dendritic cell function, there is now justification to test whether the alteration of CD101 function affects autoimmune islet destruction.

Triggering CD101 molecule on human cutaneous dendritic cells inhibits T cell proliferation via IL-10 production

Since the CD101 molecule is expressed on a major subpopulation of HLA-DR(+), CD1a(+), CD1c(+) cutaneous dendritic cells (DC), we studied the functional role of CD101 on cutaneous DC. Anti-CD101 monoclonal antibody (mAb) inhibited the proliferation of T cells induced by cutaneous DC. There was a synergistic inhibition between anti-CD101 mAb and anti-CD86/anti-CD80 mAb. Anti-CD101 mAb exerted its inhibitory effect when binding to the CD101 expressed on cutaneous DC. No positive role of CD101 putative ligand expressed by T cells in T cell proliferation was demonstrated, as T cells proliferated in response to soluble anti-CD3 mAb in the presence of CD86-transfected cells but not in the presence of CD101-transfected cells. Of major significance is the fact that IL-10 was produced by cutaneous DC after CD101 triggering with anti-CD101 mAb, while IL-10 secretion was up-regulated in mixed cutaneous DC-T cell cultures after CD101 triggering. Furthermore, IL-10-neutralizing mAb could reverse the inhibition induced by anti-CD101 mAb. Our results demonstrate that the CD101 triggering on cutaneous DC inhibits T cell proliferation via IL-10 production, suggesting an important regulatory role played by the CD101 molecule on DC during T cell activation.

CD101 expression by Langerhans cell histiocytosis cells

AIMS

Our objective was to study the expression of a recently identified cell surface molecule, CD101 and in Langerhans cell histiocytosis (LCH) patients as CD101 has been shown to be present on dendritic cells. We wanted to determine if CD101 expression could be helpful for the diagnosis of LCH in conjunction with other markers (CD1a, S100 protein), and could be predictive of the evolution and dissemination of the disease.

METHODS AND RESULTS

The expression of CD101 was studied by immunohistochemical technique in 11 cases of Langerhans cell histiocytosis on frozen sections. The expression of CD101 was positive in nine cases, high in six cases and low in three cases. There was no expression in the other two cases. No correlation with the evolution, the localization or the dissemination of the disease could be evidenced.

CONCLUSIONS

CD101 is a new phenotypic marker that might be useful in combination with other markers for the diagnosis of LCH. However, as the anti-CD101 antibody works only in frozen sections, its value is limited compared to anti-CD1a antibody.