Effects of Live Attenuated Vaccine and Wild Type Strains of Edwardsiella ictaluri on Phagocytosis, Bacterial Killing, and Survival of Catfish B Cells.

Adef O Kordon,Lesya M Pinchuk,Safak Kalindamar,Wei Tan,Kara Majors,Hossam Abdelhamed,Attila Karsi

doi:10.3389/fimmu.2019.02383

Adef O Kordon, Lesya M Pinchuk + Show 5 more

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https://doi.org/10.3389/fimmu.2019.02383

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Abstract

Edwardsiella ictaluri, a Gram-negative facultative intracellular pathogen, is the causative agent of enteric septicemia of catfish (ESC). The innate functions of B cells have been demonstrated in several teleost fish, including zebrafish, rainbow trout, and channel catfish. Recently, our group has developed several protective E. ictaluri live attenuated vaccines (LAVs). However, the innate role of catfish B cells to phagocytose and destroy E. ictaluri wild-type (WT) and live attenuated vaccine (LAV) strains has not been evaluated. In this study, we assessed the efficacy of E. ictaluri WT and two LAVs on phagocytosis, microbial killing, and survival of catfish anterior kidney (AK) B cells. Initially, we documented active uptake of E. ictaluri WT and two LAVs in B cells by flow cytometry and light microscopy. Then, we observed the E. ictaluri strains-induced phagosome and/or phagolysosome formation in the cytoplasm of catfish magnetically sorted IgM+ B cells. Furthermore, we demonstrated that AK B cells were able to destroy the internalized E. ictaluri WT and LAV strains efficiently. Finally, we documented early and late apoptotic/necrotic manifestations induced by E. ictaluri in catfish AK B cells. In conclusion, our results suggest that both LAVs and WT strain initiate similar innate immune responses such as active phagocytic uptake, induced bactericidal activity as well as promote early and late apoptotic changes in catfish B cells. Our data suggest that phagocytic and microbicidal B cells may serve as professional APCs in initiation of protective adaptive immune responses against ESC in channel catfish.

Highlights

The primary function of B cells in the humoral branch of adaptive immunity is to secrete antibodies of increasing affinity and maintain an immunological memory [1]
We determined the active uptake of E. ictaluri WT and two live attenuated vaccine (LAV) strains in catfish B cells (Figure 2A)
We used an additional protocol for active bacterial uptake assessment in the anterior kidney (AK) B cells exposed to the WT E. ictaluri strain opsonized with normal catfish serum (Figure 2B)

Summary

Introduction

The primary function of B cells in the humoral branch of adaptive immunity is to secrete antibodies of increasing affinity and maintain an immunological memory [1]. Two subsets of mammalian B cells, marginal zone (MZ) and B-1 B cells, were classified as “innate B lymphocytes” based on their developmental, phenotypic, and Innate B Cell Responses to E. ictaluri functional characteristics contributing to innate immune responses, such as phagocytosis [3, 4]. Phagocytic B cells from the peritoneal cavity were able to ingest bacteria, produce mature phagolysosomes, destroy the ingested bacteria and present the bacterial antigens to CD4+ T cells [5]. The ability of B cells to uptake soluble, particulate and bacterial antigens by phagocytosis has been documented in zebrafish and Atlantic salmon [11, 12]. The phagocyting B cells that possessed phagolysosomes were described in rainbow trout suggesting their essential role in bacterial killing [6, 13]. Contrary to other teleost fish, the large amount of phagocytic B cells has been found in catfish blood [6, 14]

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