IgD-transcript positive cells suggest hypersensitivity in feed-related intestinal inflammation in the Atlantic salmon

CCR7A defines a subpopulation of IgD+IgM- B cells with higher IgD secreting capacity in the rainbow trout skin

B cells exclusively expressing IgD on the cell surface (IgD+IgM- B cells) have been identified in mammals, where they seem to play a still not well-defined role in peripheral tolerance. These cells have also been reported in catfish (Ictalurus punctatus) peripheral blood and in several mucosal tissues of rainbow trout (Oncorhynchus mykiss), including gut, gills and skin. As in mammals, the precise function of these cells remains obscure, yet, in rainbow trout mucosal surfaces, these cells have been shown to be differentiated to plasma-like cells. Interestingly, in the gills, these IgD+IgM- B cells expressed high levels of the CC chemokine receptor 7 (CCR7), receptor that in mammals controls the migration of B and T cells to secondary lymphoid organs. In this work, we have established that this is also true for the trout skin, where CCR7 defines a specific subset of IgD+IgM- B cells that are further differentiated to a plasma-like profile than those not expressing CCR7. These findings increase the current understanding of this enigmatic B cell population and point to CCR7 as a key differentiation marker for these cells.

There and back again? A B cell's tale on responses and spatial distribution in teleosts

Teleost B cells are of special interest due to their evolutionary position and involvement in vaccine-induced adaptive immune responses. While recent progress has revealed uneven distribution of B cell subsets across the various immune sites and that B cells are one of the early responders to infection, substantial knowledge gaps persist regarding their immunophenotypic profile, functional mechanisms, and what factors lead them to occupy different immune niches. This review aims to assess the current understanding of B cell diversity, their spatial distribution in various systemic and peripheral immune sites, how B cell responses initiate, the sites where these responses develop, their trafficking, and the locations where long-term B cell responses take place.