Abstract
Dendritic cells (DCs) are highly specialized antigen-presenting cells that bridge innate and adaptive immune responses in vertebrates, being key modulators in the initiation of specific responses. Although teleost fish present the main elements of a fully developed adaptive immune system, not many studies have focused on identifying specific DC subsets in teleost species. Previous work from our group identified in rainbow trout (Oncorhynchus mykiss) skin a DC subpopulation co-expressing CD8α and major histocompatibility complex II β on the cell surface. Interestingly, these CD8+ DCs expressed common unique markers of mammalian cross-presenting DCs, a DC subset with an important role in antigen presentation and activation of CD8+ T cytotoxic lymphocytes. In this study, we have identified a similar DC subset in rainbow trout gills that also transcribes molecules uniquely expressed on diverse mammalian cross-presenting DC populations such as CD8, CD103, CD141, Batf3, IFN regulatory protein 8, and toll-like receptor 3. Hence, we have undertaken a broad phenotypic and functional characterization of this new DC subset that includes the confirmation of novel capacities for DCs in teleost, such an IgM-binding capacity and responsiveness to CD40 ligand. Furthermore, our results show that in gills, this DC subset shows some different phenotypic and functional characteristics when compared with their homologs in the skin, suggesting an adaptation of the cells to different mucosal tissues or different maturation status depending on their location. Our findings contribute to increase our knowledge on fish cross-presenting DCs, an important cell population to take into account for the future design of mucosal vaccination strategies.
Highlights
Dendritic cells (DCs) are professional antigen-presenting cells (APCs) that play a key role orchestrating adaptive immune responses
Because in mammals cross-presenting DCs are found in the lungs, we examined whether a CD8+ DC subset equivalent to that previously reported in rainbow trout skin [10] was found in gills
A subset of cells expressing surface CD8 and high levels of surface major histocompatibility complex (MHC) II cells were found in the gills, representing 1.29% of the cells in the myeloid gate (Figure 1A, top panels), in a similar trend to that seen on the spleen, where this subset was found in a similar percentage (Figure 1A, bottom panels)
Summary
Dendritic cells (DCs) are professional antigen-presenting cells (APCs) that play a key role orchestrating adaptive immune responses. DCs express a wide range of pattern recognition receptors including toll-like receptors (TLRs) that allow them to sense foreign antigens. Cross-Presenting DCs in Teleost Gills the capacity to internalize antigens, process them and present them in the context of major histocompatibility complex (MHC) I or MHC II to T cells [2]. Unlike other phagocytes such as macrophages or neutrophils, DCs are not involved in pathogen clearance. Phagosomal degradation and acidification are much lower in DCs than in other phagocytes, and the antigen is best preserved and a wider range of peptides are presented in MHC I and MHC II molecules, being this the reason for the increased capacity of DCs to prime and stimulate T cells [3]
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