B Cell Functions Can Be Modulated by Antimicrobial Peptides in Rainbow Trout Oncorhynchus mykiss: Novel Insights into the Innate Nature of B Cells in Fish.

Nu Zhang,Peng Wang,Jia-Le Li,Dan-Dan Chen,Pin Nie,Xu-Jie Zhang,Yong-An Zhang

doi:10.3389/fimmu.2017.00388

Abstract

B cells in fish were recently proven to have potent innate immune activities like macrophages. This inspired us to further explore the innate nature of B cells in fish. Moreover, antimicrobial peptides (AMPs) are representative molecules of innate immunity, and they can modulate the functions of macrophages. These make fish an appropriate model to study the interactions between B cells and AMPs. Interestingly, the results in this study revealed that the IgM+ and IgT+ B cells of rainbow trout could express multiple AMP genes, including four cathelicidin genes and one β-defensin gene. The expression levels of the cathelicidin genes were obviously higher than that of the β-defensin gene. Further studies revealed that intracellular, extracellular, in vitro, and in vivo stimulations could significantly increase the expression of the cathelicidin genes in trout IgM+ and IgT+ B cells but not the expression of the β-defensin gene, indicating that cathelicidin peptides are the main innate immune effectors of trout B cells. More interestingly, we found that cathelicidin peptides could significantly enhance the phagocytic, intracellular bactericidal, and reactive oxygen species activities of trout IgM+ and IgT+ B cells, a phenomenon previously reported only in macrophages, and these activities might also be mediated by the P2X7 receptor. These results collectively suggest that B cells play multiple roles in the innate immunity of fish, and they provide new evidence for understanding the close relationship between B cells and macrophages in vertebrates.

Highlights

The immune system of fish is composed of an innate immune system and an adaptive immune system
Since CATH-2a and CATH-2b are highly homologous genes (99% cDNA sequence identity), the PCR products were sequenced to verify the co-expression of both genes in trout IgM+ and IgT+ B cells, and the results showed that the expression level of CATH-2a was much higher than that of CATH-2b
Since antimicrobial peptides (AMPs) represent an evolutionarily old component of the innate immune system of animals, it was assumed that investigating the interactions between fish B cells and AMPs would provide novel insights into the innate nature of B cells in lower vertebrates

Summary

Introduction

The immune system of fish is composed of an innate immune system and an adaptive immune system. Phagocytosis, one of the innate immune responses, plays important roles in the defense against the invasion of pathogenic bacteria, as well as in the initiation of the adaptive immune responses [2, 3]. The phagocytosis of pathogenic bacteria is mainly conducted by professional phagocytes, such as monocytes, macrophages, and granulocytes [4]. Unlike these phagocytes, early studies have proven that primary. Recent studies demonstrated that B cells in fish have potent in vitro and in vivo phagocytic abilities like macrophages [7,8,9,10]. The abovementioned reports indicate that B cells in ectotherms, especially in fish, still play multiple roles in the innate immunity

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Results

Conclusion