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Comparison of skin mononuclear phagocyte isolation techniques on function and subset definition, and the effects of collagenase blends on pathogen binding receptor cleavage., Mononuclear phagocytes are present in skin and mucosa and represent one of the first lines of defense against invading pathogens, which they detect via an array of pathogen-binding receptors expressed on their surface. However, their extraction from tissue is difficult, and the isolation technique used has functional consequences on the cells obtained. Here, we compare mononuclear phagocytes isolated from human skin using either enzymatic digestion or spontaneous migration. Cells isolated via enzymatic digestion are in an immature state, and all subsets are easily defined. However, cells isolated by spontaneous migration are in a mature state, and CD141 cross-presenting DCs (cDC1) are more difficult to define. Different pathogen-binding receptors are susceptible to cleavage by blends of collagenase, demonstrating that great care must be taken in choosing the correct enzyme blend to digest tissue if carrying out pathogen-interaction assays. Finally, we have optimized mononuclear phagocyte culture conditions to enhance their survival after liberation from the tissue.

Epidermal Langerhans cells (eLCs) uniquely express the C-type lectin receptor langerin in addition to the HIV entry receptors CD4 and CCR5. They are among the first target cells to encounter HIV in the anogenital stratified squamous mucosa during sexual transmission. Previous reports on the mechanism of HIV transfer to T cells and the role of langerin have been contradictory. In this study, we examined HIV replication and langerin-mediated viral transfer by authentic immature eLCs and model Mutz-3 LCs. eLCs were productively infected with HIV, whereas Mutz-3 LCs were not susceptible because of a lack of CCR5 expression. Two successive phases of HIV viral transfer to T cells via cave/vesicular trafficking and de novo replication were observed with eLCs as previously described in monocyte-derived or blood dendritic cells, but only first phase transfer was observed with Mutz-3 LCs. Langerin was expressed as trimers after cross-linking on the cell surface of Mutz-3 LCs and in this form preferentially bound HIV envelope protein gp140 and whole HIV particles via the carbohydrate recognition domain (CRD). Both phases of HIV transfer from eLCs to T cells were inhibited when eLCs were pretreated with a mAb to langerin CRD or when HIV was pretreated with a soluble langerin trimeric extracellular domain or by a CRD homolog. However, the langerin homolog did not inhibit direct HIV infection of T cells. These two novel soluble langerin inhibitors could be developed to prevent HIV uptake, infection, and subsequent transfer to T cells during early stages of infection.

Introduction The mechanism by which immunity to herpes simplex virus (HSV) is initiated is not completely defined. HSV initially infects the stratified squamous epithelium of the anogenital mucosa prior to entering nerve endings. We have recently reported that topical application of HSV-1 to human foreskin explants results in infection of epidermal Langerhans cells (LCs) which then emigrate into the dermis where they expressed the maturation marker CD80 and formed large cell clusters with BDCA3+ subsets of DC-SIGN+ and dermal dendritic cells (DCs) and. HSV-expressing LC fragments were observed inside the dermal DCs/macrophages. No other infected epidermal cells interacted with the dermal DCs (Kim et al. Plos Pathogens, 2015). Methods Therefore, we isolated LCs and dermal DCs from large abdominal skin specimens by collagenase digestion and flow sorting. LCs were pulsed with fluorescent tagged HSV and co-cultured with a subset of (BDCA3+) dermal DCs. Results All infected LCs showed markers of apoptosis at 18 hr p.i. Approximately 50% of BDCA3+ DCs co-localised with infected LCs and in some cases fragments of infected LCs were observed within the dermal DC cytoplasm. Such colocalizaton of HSV antigen bearing LCs and dermal DC subsets, was also detected within biopsies of initial genital herpes lesions. The mechanism of interaction of apoptotic LCs and dermal DCs, and uptake by phagocytosis are being determined. Conclusion Thus, a viral antigen relay takes place where HSV infected LCs slowly die by apoptosis during migration to the dermis and are taken up by dermal DCs by phagocytosis for subsequent antigen presentation. This provides a rationale for targeting these dermal DCs for mucosal or perhaps intradermal HSV immunisation. Disclosure of interest statement No pharmaceutical grants were received in the development of this study.