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

Abstract

Mucosal surfaces require balancing different physiological roles and immune functions. In order to effectively achieve multifunctionality, mucosal epithelia have evolved unique microenvironments that create unique regional immune responses without impairing other normal physiological functions. Whereas examples of regional immunity are known in other mucosal epithelia, to date, no immune microenvironments have been described in the nasal mucosa, a site where the complex functions of olfaction and immunity need to be orchestrated. In this study we identified for the first time the presence of CD8α+ cells in the rainbow trout (Oncorhynchus mykiss) nasal epithelium. Nasal CD8α+ cells display a distinct phenotype suggestive of CD8+ T cells with high integrin β2 expression. Importantly, nasal CD8α+ cells are located in clusters at the mucosal tip of each olfactory lamella but scattered in the neuroepithelial region. The grouping of CD8α+ cells may be explained by the greater expression of CCL19, ICAM-1, and VCAM-1 in the mucosal tip compared to the neuroepithelium. Whilst viral antigen uptake occurred via both tip and lateral routes, tip resident MHC-II+ cells are located significantly closer to the lumen of the nasal cavity than their neuroepithelial counterparts, therefore having quicker access to invading pathogens. Our studies reveal for the first time compartmentalized mucosal immune responses within the nasal mucosa of a vertebrate species, a strategy that likely optimizes local immune responses while protecting olfactory sensory functions.

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

“…These results were consistent regardless of the source of cells used (HKLs, SLs or GLs) in vitro even when we pre-activated leucocytes were used. We have previously shown that HK and gut CD8α + cells express CCR7 (29) indicating that the source of cells used in our studies should not be reason why chemotaxis results were negative. Some reports have shown the importance of PGE2 on the migratory ability of CCL19 in mammalian monocytes (83–86).…”

“…Leucocyte recruitment is easily visualized by histological examination due to the presence of an enlarged LP in the olfactory lamellae of vaccinated animals compared to controls (27). Furthermore, we have shown in the past that nasal delivery of IHNV vaccine results in MHC-II + responses in the OO of trout (29). Since in vitro Transwell assays may not mimic in vivo immune responses, we delivered rCK12a I.N.…”

“…delivery of IHNV vaccine changes the morphology of the MHC-II + cells dramatically (29). The present study revealed that delivery of rCK12a (I.N.)…”

“…We also showed that nasal vaccination of rainbow trout with a live attenuated viral vaccine results in both local nasal and systemic immune responses (27, 29). The latter opened up many questions including what are the molecular mechanisms that explain the protective effects of nasal vaccines in fish and how are nasal and systemic immune responses orchestrated in cold-blooded vertebrates.…”

“…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.…”