Dendritic Cell Immunophenotyping Assays

Dendritic cells (DCs) vital to both the innate and adaptive immune systems. DCs capture, process, and present antigens via the Major Histocompatibility Complex (MHC) class I and class II to prime naïve T-cells to initiate the primary immune response ^[1-3]. Alongside antigen presentation, DCs can utilise a repertoire of T-cell stimulatory cytokines or directly interact with co-stimulatory molecules of the peptide-MHC complex specific T-cell receptor (TCR) via their ligands e.g., CD80 and CD86, to enhance T-cell activation, differentiation, polarisation, and function ^[3]. Due to their exceptional capabilities, DCs alone can initiate and direct the specificity and magnitude of all antigen-specific immune responses ^[3].

There are several different types of DCs, each strategically located in various tissues to capture and process antigens for the activation of different arms of the immune system ^[1,2]. DC subsets are classified according to their cell lineage, driven by differential expression of key transcription factors e.g., interferon regulatory factor (IRF4) and IRF8, cytokines, chemokines, and adhesion molecule to drive their differentiation ^{[1, 3]}. At PeploBio, we currently offer a wide panel of markers for the characterization of key DCs in biological fluids and tissue extracts.

Myeloid/conventional DC1s (cDC1) are specialized in cross-presentation of antigens to CD8⁺ cytotoxic T-cells ^[1]. cDC1 cell maturation is regulated by transcription factors IRF8, BAFT3 and ID2 ^[1,3]. They excel at capturing and presenting antigens from intracellular pathogens, such as viruses and some tumours. They are primarily found in peripheral tissues and secondary lymphoid organs like lymph nodes. cDC1s are characterised by conventional markers CD141/BDCA1 ^[1].

Myeloid/conventional DC2s (cDC2) are primarily involved in presenting antigens to CD4⁺ T-helper cells ^[1]. They participate in immune responses against extracellular pathogens and contribute to antibody production. Like cDC1s, they are also found in peripheral tissues and secondary lymphoid organs. cDC2 cells can be identified by phenotypic markers CD1c/BDCA1, CD11b and CD11c, and differential transcription factors ID2, ZEB2, IRF4 and Notch2/KLF4 ^[1].

Langerhans cells (LCs) are a specialized subset of immature myeloid DCs located in the epidermis of the skin ^[1-3]. LCs are involved in immune surveillance and are often the first to encounter and capture antigens from the skin, including allergens and pathogens. Although LCs were initially identified by the presence of Birbeck granules, they are now further characterised by the expression of markers langerin/CD207, CD1a and E-cadherin and transcription factors ID2 and RUNX3 ^{[1, 2, 4]}.

Plasmacytoid DCs (pDCs) are typically found in blood and secondary lymphoid organs ^[1].  Plasmacytoid DCs present antigens to T-cells, although not as efficiently as cDCs. Among DCs, pDCs are distinct in its ability to produce large quantities of type I interferons such as INFα, INFg and INFW, as an antiviral response. Unlike cDCs, pDCs use TLR7 and TLR9 for virus detection ^[2]. Unsurprisingly, many conventional pDC surface receptors are aptly suited for these functions. Characteristic markers of pDCs include CD123, CD303/CLEC4C/BDCA2 and CD304/NRP1/BDCA4 but CD303 is most robust for their identification ^[1,2]. pDC differentiation is thought to be largely driven by transcription factors E2-2, ZEB2, IRF4 and IRF8 ^[1].

As the name implies, monocyte-derived DCs (Mo-DC) arise from monocytes recruited into tissue in response to inflammation or infection. IL4 and GM-CSF can be used to induce human Mo-DCs from monocytes in vitro and MAFB and KLF4 have been identified as differential transcription factors ^{[1, 5]}. Mo-DCs can perform antigen presentation or initiate cytokine production, depending on the context. They are unique in their ability to cross present antigens to CD8⁺ T-cells directly in peripheral tissue which leads to the prompt activation of tissue-resident CD8⁺memory T-cells ^[5]. Phenotypic markers for Mo-DCs overlap with other DCs such as CD11a and CD1c/BDCA1 with cDC2 cells or CD1a with LCs. Their identification in heterogenous cell populations can be aided with the use of extended markers such as SIRPA, S100A8, S100A9, CD206 and DC-SIGN/CD209^[1].