Porcine peripheral blood dendritic cells and natural interferon‐producing cells

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Abstract
Peripheral blood contains two major particular infrequent dendritic cells (DC) subsets linking the innate and specific immune system, the myeloid DC and plasmacytoid DC equivalent to the natural interferon‐producing cells (NIPC). The functional characterization of these cells demands large volumes of blood, making a large animal model more appropriate and beneficial for certain studies. Here, two subsets of porcine blood mononuclear cells expressing swine workshop cluster 3 (SWC3, a SIRP family member), are described and compared to monocytes. The blood DC specialized in T‐cell stimulation were major histocompatibility complex (MHC) class II+, CD80/86+, CD1+/–, CD4−, and in contrast to monocytes CD14−. A CD16− and a CD16+ subset could be discriminated. Granulocyte–macrophage colony‐stimulating factor and interleukin‐3 were survival factors for this DC subset, and culture induced an up‐regulation of MHC class II and CD80/86. The second subset described, are porcine NIPC, typically CD4++, MHC class IIlow, CD80/86low, CD1−, CD8−/low, CD16−/low and CD45RA−/low. Porcine NIPC had high interleukin‐3 binding capacity, and survived in response to this cytokine. Their unique function was strong interferon type I secretion after virus stimulation. Both subsets were endocytically active when freshly isolated, and down‐regulated this activity after in vitro maturation. Taken together, the present report has delineated porcine blood DC and NIPC, permitting a more detailed understanding of innate immune defences, particularly in response to infections.