Rag1−/− Mutant Zebrafish Demonstrate Specific Protection following Bacterial Re-Exposure

Abstract

BackgroundRecombination activation gene 1 deficient (rag1−/−) mutant zebrafish have a reduced lymphocyte-like cell population that lacks functional B and T lymphocytes of the acquired immune system, but includes Natural Killer (NK)-like cells and Non-specific cytotoxic cells (NCC) of the innate immune system. The innate immune system is thought to lack the adaptive characteristics of an acquired immune system that provide enhanced protection to a second exposure of the same pathogen. It has been shown that NK cells have the ability to mediate adaptive immunity to chemical haptens and cytomegalovirus in murine models. In this study we evaluated the ability of rag1−/− mutant zebrafish to mount a protective response to the facultative intracellular fish bacterium Edwardsiella ictaluri.Methodology/Principal FindingsFollowing secondary challenge with a lethal dose of homologous bacteria 4 and 8 weeks after a primary vaccination, rag1−/− mutant zebrafish demonstrated protective immunity. Heterologous bacterial exposures did not provide protection. Adoptive leukocyte transfers from previously exposed mutants conferred protective immunity to naïve mutants when exposed to homologous bacteria.Conclusions/SignificanceOur findings show that a component of the innate immune system mounted a response that provided significantly increased survival when rag1−/− mutant zebrafish were re-exposed to the same bacteria. Further, adoptive cell transfers demonstrated that kidney interstitial leukocytes from previously exposed rag1−/− mutant zebrafish transferred this protective immunity. This is the first report of any rag1−/− mutant vertebrate mounting a protective secondary immune response to a bacterial pathogen, and demonstrates that a type of zebrafish innate immune cell can mediate adaptive immunity in the absence of T and B cells.

Proinflammatory Caspase A Activation and an Antiviral State Are Induced by a Zebrafish Perforin after Possible Cellular and Functional Diversification from a Myeloid Ancestor

“…Interestingly, rainbow trout perforin is also induced in the monocyte/macrophage-like RTS-11 cell line after viral hemorrhagic septicemia virus infection [38], suggesting that teleost perforins are commonly expressed in the myeloid cell population. These results also agreed with our results obtained in RAG1 -/- mutant zebrafish, which have a reduced lymphocyte-like cell population [39]. RAG1 -/- fish have more perforin mRNAs in the kidney than RAG1 +/+ fish, including more expression of prf19b , which is probably related to their increased myelomonocyte population compared with that of RAG1 +/+ fish [40].…”

B Cells in Teleost Fish Act as Pivotal Initiating APCs in Priming Adaptive Immunity: An Evolutionary Perspective on the Origin of the B-1 Cell Subset and B7 Molecules

“…All fish used in the experiments were offspring of a single AB strain parent pair after five generations of partial inbreeding (26,27). Only healthy fish, as determined by general appearance and level of activity, were used for the study.…”

Perspectives on antigen presenting cells in zebrafish

“…For example, zebrafish B cells appear to have little to no role in the response against Edwardsiella tarda (Yang et al, 2013). Additionally, Rag1 −/− zebrafish, which lack functional T and B cells, immunized with Edwardsiella ictaluri demonstrate greater survival against subsequent specific challenge compared to non-immunized fish (Petrie-Hanson et al, 2009; Hohn and Petrie-Hanson, 2012). Thus, zebrafish may be capable of mounting an acquired immune response in the absence of B and T cell activity.…”

“…In fact, Ikaros mutant fish, which lack most B and T cells do not have impaired survival rates (Schorpp et al, 2006). Furthermore, Rag1 mutant fish, which completely lack B and T lymphocytes, are remarkably resistant to secondary infection and are suggested to achieve specific protective immunity through innate mechanisms (Petrie-Hanson et al, 2009; Hohn and Petrie-Hanson, 2012). This contrasts with the apparent susceptibility of zebrafish to infection in the absence of key innate immune components.…”