Identification of Teleost Skin CD8α+ Dendritic-like Cells, Representing a Potential Common Ancestor for Mammalian Cross-Presenting Dendritic Cells

Abstract

Although fish constitute the most ancient animal group in which an acquired immune system is present, the presence of dendritic cells (DCs) in teleosts has been addressed only briefly, and the identification of a specific DC subset in teleosts remained elusive because of the lack of specific Abs. In mice, DCs expressing CD8α+ in lymphoid tissues have the capacity to cross-present extracellular Ags to T cells through MHC I, similarly to tissue-derived CD103+ DCs and the human CD141+ DC population. In the current study, we identified a large and highly complex subpopulation of leukocytes coexpressing MHC class II and CD8α. This CD8α+ MHC II+ DC-like subpopulation constituted ∼1.2% of the total leukocyte population in the skin, showing phenotypical and functional characteristics of semimature DCs that seem to locally regulate mucosal immunity and tolerance in a species lacking lymph nodes. Furthermore, we identified trout homologs for CD141 and CD103 and demonstrated that, in trout, this skin CD8+ DC-like subpopulation expresses both markers. To our knowledge, these results provide the first evidence of a specific DC-like subtype in nonimmune tissue in teleosts and support the hypothesis of a common origin for all mammalian cross-presenting DCs.

Tissue Microenvironments in the Nasal Epithelium of Rainbow Trout (Oncorhynchus mykiss) Define Two Distinct CD8α+ Cell Populations and Establish Regional Immunity

“…We found very low levels of expression of CD141 in systemic (HK) and nasal CD8 + T cells but high expression in gut CD8 + cells. Our results are in agreement with a previous study that showed low CD141 expression in trout splenic CD8 + T cells (32). With regards to the high CD103 and CD141 expression in gut, it is worth mentioning that teleost and mammalian DCs can also express CD103 and CD141 (32, 67–69) and therefore the presence of few CD8 + /DC-SIGN−/CD103 + /CD141 + DCs or DC progenitors in the gut CD8α + cell population, although unlikely, cannot be ruled out.…”

“…Previously, CD103 and integrin β7 were shown to be abundantly expressed in thymic and mucosal (gill and gut) trout CD8α + lymphocytes (31). Moreover, unlike their mucosal counterparts, trout splenic CD8 + T cells do not express CD103 (32). Here we show that trout nasal CD8α + lymphocytes have a significantly lower expression of CD103 but much higher expression of integrin β2 than gut CD8α + lymphocytes.…”

“…Based on our microscopy results, no double CD8 + /MHC-II + cells were identified in NALT. Recently, CD8 + /MHC-II + cells within the myeloid gate with a DC-like cell phenotype have been characterized in the skin of rainbow trout (32). Thus, it seems that this population is absent at this mucosal site in trout.…”

“…For immunostaining, trout olfactory organs were snap frozen in OCT for cryosectioning and 5-µm-thick cryosections were post-fixed in acetone followed by 4% paraformaldehyde and labeled with rat anti-trout CD8α antibody (31) followed by FITC-donkey anti-rat IgG (Jackson Immunoresearch). For detection of MHC-II+ cells in the nasal mucosa, cryosections were stained with mouse anti-trout MHC-II β-chain IgG (2 µg/ml) (32) followed by Alexa 647 donkey anti-mouse IgG (2 µg/ml). For detection of IHNV, a pool of anti-IHNV monoclonal antibodies containing Mabs 1H8, 6A7 and 5AG (2 µg/ml) followed by Cy3 anti-mouse IgG (Jackson Immunoresearch, 1 µg/ml) was used.…”

CK12a, a CCL19-like Chemokine That Orchestrates both Nasal and Systemic Antiviral Immune Responses in Rainbow Trout

“…rCK12a treated and i.p. rCK12a treated (n = 3) rainbow trout were stained with anti-trout CD8α + and MHC-II antibody as explained elsewhere (29, 61, 62). Nuclei were stained with DAPI DNA stain and slides were observed under a Nikon Ti fluorescence microscope.…”