Abstract
Dendritic cells (DC) are multi-functional cells that bridge the gap between innate and adaptive immune systems. In bovine, significant information is lacking on the precise identity and role of peripheral blood DC subsets. In this study, we identify and characterize bovine peripheral blood DC subsets directly ex vivo, without further in vitro manipulation. Multi-color flow cytometric analysis revealed that three DC subsets could be identified. Bovine plasmacytoid DC were phenotypically identified by a unique pattern of cell surface protein expression including CD4, exhibited an extensive endoplasmic reticulum and Golgi apparatus, efficiently internalized and degraded exogenous antigen, and were the only peripheral blood cells specialized in the production of type I IFN following activation with Toll-like receptor (TLR) agonists. Conventional DC were identified by expression of a different pattern of cell surface proteins including CD11c, MHC class II, and CD80, among others, the display of extensive dendritic protrusions on their plasma membrane, expression of very high levels of MHC class II and co-stimulatory molecules, efficient internalization and degradation of exogenous antigen, and ready production of detectable levels of TNF-alpha in response to TLR activation. Our investigations also revealed a third novel DC subset that may be a precursor of conventional DC that were MHC class II+ and CD11c−. These cells exhibited a smooth plasma membrane with a rounded nucleus, produced TNF-alpha in response to TLR-activation (albeit lower than CD11c+ DC), and were the least efficient in internalization/degradation of exogenous antigen. These studies define three bovine blood DC subsets with distinct phenotypic and functional characteristics which can be analyzed during immune responses to pathogens and vaccinations of cattle.
Highlights
Dendritic cells (DC) are a heterogeneous population of cells that play a critical role in initiation and linking of the innate and adaptive immune response [1]
We demonstrate that three distinct DC subsets could be identified in bovine peripheral blood: one DC subset corresponds to plasmacytoid DC (pDC) that express CD4, and two conventional dendritic cells (cDC) populations that express MHC class II
We identified two populations of putative DC: CD42 MHC class II+ (0.09160.022% of peripheral blood mononuclear cells (PBMC), n = 6), and CD4+ MHC class II2 (0.008560.003% of PBMC, n = 6), that correspond to cDC and pDC, respectively (Figure 1E)
Summary
Dendritic cells (DC) are a heterogeneous population of cells that play a critical role in initiation and linking of the innate and adaptive immune response [1]. Several studies have generated bovine moDC from monocyte precursors isolated from peripheral blood to assess their function in response to pathogen infections [16,17,18,19,20]. A recent study has demonstrated that investigation of in vitro derived moDC does not accurately represent in vivo populations [21]. These investigators show that in vitro, moDC had an increased capacity for proteolysis, a characteristic exhibited by macrophages, but not ex vivo isolated DC [21]. The physiological relevance of in vitro derived moDC is problematic, and caution is necessary when using moDC as a model for DC
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