Analysis of long-lived plasma cell production and regulation: Implications for vaccine design for aquaculture

The importance of long-lived plasma cells (LPC), over other antibody-secreting cells (ASC), in the generation of long-term immunity and memory in mammals has been the focus of considerable recent interest. Studies suggest that long-term immunity to infectious agents, such as viruses, may be primarily due to the expression of antibody from this unique population of ASC. Unfortunately due to the relative paucity of studies on teleost immune cells, virtually no information exists on LPC, or ASC diversity in these species. However, recent work in our laboratory has revealed that trout possess functionally diverse ASC populations, including plasmablasts, short-lived plasma cells and long-lived plasma cells. Importantly, as in mammals, these populations are not uniformly distributed among all immune tissues. This is of particular significance with respect to long-lived plasma cells, which appear to exclusively reside within, or migrate to, the anterior kidney. Previous teleost studies have operated under the assumption that all ASC are plasma cells. However, we have found that virtually the entire peripheral blood lymphocyte (PBL) ASC response is comprised of plasmablasts, while the trout plasma cell response resides within the anterior kidney. Thus, the assumption that the in vitro behavior of ASC from PBL is identical to that of plasma cells and that they are responsible for in vivo antibody responses, is flawed. Based on this information we propose an alternative model of functional differentiation and regional distribution of ASC in the trout and pose some important implications for the development of immunological memory and aquaculture vaccines based on this model.