CD209 Human

What is CD209 and what are its primary functions in the human immune system?

CD209 (also known as DC-SIGN or Dendritic Cell-Specific ICAM-3-Grabbing Non-Integrin) is a C-type lectin receptor primarily expressed on immature dendritic cells (DCs). It functions as a pathogen-recognition receptor that mediates the endocytosis of pathogens which are subsequently degraded in lysosomal compartments. The receptor returns to the cell membrane surface, and pathogen-derived antigens are presented to T-cells via MHC class II proteins to initiate adaptive immune responses .

CD209 serves as a high-affinity receptor for ICAM2 and ICAM3 by binding to mannose-like carbohydrates. It may act as a DC rolling receptor that mediates transendothelial migration of DC precursors from blood to tissues by binding endothelial ICAM2. Additionally, it regulates DC-induced T-cell proliferation by binding to ICAM3 on T-cells in the immunological synapse formed between DCs and T-cells .

What is the molecular structure of CD209 protein?

The CD209 protein is organized into four distinct domains:

• A C-terminal carbohydrate recognition domain (responsible for pathogen binding)

• A flexible tandem-repeat neck domain (provides structural flexibility)

• A transmembrane region (anchors the protein to the cell membrane)

• An N-terminal cytoplasmic domain (involved in internalization processes)

This structured organization enables CD209 to bind to various pathogens through its carbohydrate recognition domain while facilitating signal transduction and internalization. The neck domain contains polymorphisms that have been associated with protection from HIV-1 infection, highlighting its functional importance .

Which pathogens are recognized by CD209 in humans?

CD209 acts as an attachment receptor for numerous pathogens, including:

Viruses:

• HIV-1 and HIV-2

• Ebolavirus

• Cytomegalovirus

• Hepatitis C virus (HCV)

• Dengue virus

• Measles virus

• Herpes simplex virus 1

• Influenza A virus

• SARS-CoV

• Japanese encephalitis virus

• Lassa virus and Marburg virus

• Respiratory syncytial virus

• West Nile virus

Bacteria and other pathogens:

• Recognizes high mannose N-linked oligosaccharides in various bacterial pathogens including:

  • Leishmania pifanoi LPG

  • Lewis-x antigen in Helicobacter pylori LPS

  • Mannose in Klebsiella pneumoniae LPS

  • Di-mannose and tri-mannose in Mycobacterium tuberculosis ManLAM

  • Lewis-x antigen in Schistosoma mansoni SEA

Recognition of M. tuberculosis by dendritic cells occurs partially via CD209 .

How does the CD209/CD14+ dendritic cell population differ in inflammatory arthritis?

Recent research has identified a novel dendritic cell population characterized as CD209/CD14+ DC in both Rheumatoid Arthritis (RA) and Psoriatic Arthritis (PsA) patients. These cells express classical DC markers (HLADR, CD11c) and the Mo-DC marker (CD209), while also retaining the monocytic marker CD14 .

Key findings about these cells include:

• Increased frequency in the circulation of RA and PsA patients compared to healthy controls

• Higher expression of inflammatory cytokines (IL-1β, IL-6, IL-12, TNFα)

• Unique chemokine receptor expression and co-expression profiles

• Enrichment in inflamed joints where they display a distinct inflammatory and maturation phenotype with increased CD40 and CD80

Importantly, there are disease-specific differences between RA and PsA CD209/CD14+ DCs:

• RA CD209+ DCs show increased expression/co-expression of CCR6, CCR7, CXCR3, CXCR4, and CXCR5 when cultured with RA synovial fluid

• PsA CD209+ DCs show increased expression of chemokines CCR3, CXCL10, and CXCL11 when cultured with PsA synovial fluid

These differences may contribute to disease-specific pathogenesis mechanisms.

What methods can be used to isolate and characterize CD209+ dendritic cells?

A novel protocol for isolating CD209+ dendritic cells has been developed with the following steps:

• PBMC isolation from whole blood

• Depletion of CD3/CD19/CD56 cells (Lineage cells) by magnetic positive isolation

• Culture of lineage-negative cells with 70 ng/mL GM-CSF and 50 ng/mL IL-4 for 48 hours to spike the CD209 population

• Positive magnetic sorting using CD209 MicroBeads

This protocol achieves >96% purity of CD209+ cells. The isolated cells display heterogeneous morphological characteristics, with a mixture of elongated and round cells, suggesting various stages of differentiation/maturation .

For comprehensive characterization, multiparameter flow cytometry can be performed using markers such as:

• CD209 (FITC, PerCP/Cy5.5, or PE)

• CD14 (PE or Brilliant Violet 510)

• CD80 (APC700), CD86 (FITC), CD83 (BV711), CD40 (BV605) (maturation markers)

• HLA-DR (Brilliant Violet 785 or 421), CD11c (PerCP/Cy5.5 or PE/CY7) (DC markers)

• Chemokine receptors: CCR6, CCR7, CXCR3, CXCR4, CXCR5

How does the synovial microenvironment influence CD209+ dendritic cell development?

Research demonstrates that the synovial microenvironment substantially impacts CD209+ dendritic cell development and function. When healthy CD209+ DCs are cultured with inflammatory arthritis (IA) synovial fluid (SF), but not osteoarthritis (OA) SF, this exposure induces the development of CD209/CD14+ DCs and leads to a poly-mature phenotype .

Specific effects include:

• Increased expression of maturation markers CD40, CD80, CD83, and CD86

• Disease-specific effects on chemokine receptor expression:

  • RA SF causes increased expression/co-expression of CCR6, CCR7, CXCR3, CXCR4, and CXCR5

  • PsA SF increases expression of CCR3, CXCL10, and CXCL11

• Differential effects may be mediated by disease-specific chemokines expressed in RA versus PsA synovial fluid

This finding suggests that the local joint environment can reprogram healthy CD209+ DCs into a pathogenic phenotype, potentially contributing to disease persistence and progression.

What transcriptional differences exist in CD209+ dendritic cells between healthy individuals and those with inflammatory arthritis?

Transcriptional analysis of isolated CD209+ dendritic cells from healthy controls, PsA, and RA patients has revealed significant differences in gene expression profiles .

Key differentially expressed genes include:

• Matrix metalloproteinases: MMP9, MMP2, MMP14

• Endosomal trafficking proteins: SNX1, SNX2, LAMP1

• Pattern recognition receptors: TLR4, TREM1

• Oxidative stress enzymes: NOX2

• Cell clustering molecules: CLU

The relative expression of these genes differs between healthy controls, PsA, and RA patients, with disease-specific patterns. This suggests distinct pathogenic mechanisms may be at play in different inflammatory arthritis conditions .

How can complex co-expression patterns of chemokine receptors on CD209+ cells be analyzed?

Analysis of complex chemokine receptor co-expression on CD209+ dendritic cells requires specialized approaches:

• SPICE (Simplified Presentation of Incredibly Complex Evaluations) algorithm flow cytometric analysis:

  • Displays the frequency of chemokine receptors (CCR6, CCR7, CXCR3, CXCR4, CXCR5)

  • Visualizes co-expression patterns through arc representations

  • Enables statistical comparison between different conditions

• Multiparameter flow cytometry with appropriate controls:

  • Use Fluorescence Minus One (FMO) controls for accurate gating of chemokine receptors

  • Analyze both single expression and co-expression of multiple receptors

  • Compare patterns between health and disease states

These approaches have revealed that CD209+ DCs from PsA and RA patients show distinct chemokine receptor co-expression profiles, which may contribute to their differential trafficking and function in inflammatory conditions .

What is the role of the JAK/STAT pathway in regulating CD209/CD14+ dendritic cell function?

Research has demonstrated that the JAK/STAT pathway, but not the NF-κB pathway (driven by TNFα), regulates CD209/CD14+ DC function in inflammatory arthritis . The JAK/STAT pathway influences:

• Activation state of CD209/CD14+ DCs

• Inflammatory cytokine production

• Migratory capacity through modulation of chemokine receptor expression

Experimental approaches to study this regulation include:

• Selective JAK inhibitor treatments in vitro

• Phospho-protein analysis to assess activation of STAT proteins

• Gene expression profiling before and after JAK inhibition

• Functional migration assays to assess the impact on chemotaxis

This finding suggests that JAK/STAT inhibition could be used as a therapeutic strategy to decrease the inflammatory state of pathogenic CD209/CD14+ DCs in autoimmune arthritis conditions .

What methods can be used to study CD209-mediated antigen uptake?

To study CD209-mediated antigen uptake, researchers have developed specific protocols including:

• DQ-OVA uptake assay:

  • Incubate CD209+ cells with DQ-OVA (self-quenched conjugate of ovalbumin)

  • Compare cells incubated at 37°C (specific uptake) with cells incubated at 4°C (non-specific uptake)

  • Analyze fluorescence using flow cytometry (excitation with 488 nm laser and fluorescence using 530/30 bandpass filter)

  • Calculate percentage of cells incorporating DQ-OVA by subtracting non-specific from specific uptake

• Flow cytometric analysis of endocytic capacity:

  • Use markers of endosomal compartments (LAMP1, SNX1, SNX2)

  • Assess expression levels of endocytic machinery components

  • Compare endocytic capacity between CD209+ DCs from different patient groups

These methods allow quantitative assessment of the antigen uptake and processing capabilities of CD209+ DCs, which are critical for their function in immune responses.

How do polymorphisms in CD209 affect pathogen binding and disease susceptibility?

Polymorphisms in CD209 have been associated with differential susceptibility to infectious diseases:

• Neck region polymorphisms:

  • Associated with protection from HIV-1 infection

  • May affect the oligomerization of CD209 molecules and thus binding avidity to pathogens

• Promoter region polymorphisms:

  • Single nucleotide polymorphisms (SNPs) affect resistance and susceptibility to infectious diseases

  • rs4804803 is specifically associated with SARS severity

These polymorphisms can alter CD209's ability to recognize and bind pathogens, potentially influencing:

• Efficiency of pathogen capture and internalization

• Subsequent antigen presentation

• Initiation of appropriate immune responses

Research methodologies to study these associations include:

• Case-control genetic association studies

• In vitro binding assays with recombinant CD209 variants

• Functional assays measuring pathogen uptake and processing efficiency

What are the key future research directions for CD209 in human health and disease?

Future research on CD209 in human health and disease should focus on several promising directions:

• Therapeutic targeting of CD209/CD14+ DCs in inflammatory arthritis:

  • Further investigation of JAK/STAT inhibition effects

  • Development of CD209-specific targeting strategies

  • Exploration of methods to reprogram pathogenic DCs towards a regulatory phenotype

• Role of CD209 in emerging infectious diseases:

  • Characterization of CD209 binding to novel pathogens

  • Investigation of polymorphisms affecting susceptibility to new infectious threats

  • Development of therapeutic strategies targeting CD209-pathogen interactions

• Single-cell analysis of CD209+ DC heterogeneity:

  • Application of single-cell technologies to better understand subpopulations

  • Integration of transcriptomic, proteomic, and functional data

  • Identification of disease-specific CD209+ DC signatures

• Development of standardized protocols:

  • Refinement of isolation and characterization methods

  • Establishment of reference datasets for normal CD209+ DC phenotypes

  • Creation of validated assays for measuring CD209-mediated functions