DISCOVERY OF CYTOTOXIC KILLER IGT+ B CELLS IN FISH

03 Jun 2019
13:00 - 13:20

DISCOVERY OF CYTOTOXIC KILLER IGT+ B CELLS IN FISH

Oriol Sunyer, University of Pennsylvania

Yasuhiro Shibasaki1,2, Fumio Takizawa1,3, Michael Gonzalez4, Pierre Boudinot5, J. Oriol Sunyer1

1 Department of Pathobiology, School of Veterinary Medicine, University of Pennsylvania,
2 JSPS, Overseas Research Fellow,
3 Faculty of Marine Science and Technology, Fukui Prefectural University,
4 Children’s Hospital of Philadelphia,
5 Virologie et Immunologie Moléculaires, INRA, Université Paris-Saclay

Our previous work has shown that IgT plays a key role in teleost fish mucosal immune responses. We have demonstrated that IgT is produced by a subset of B cells that uniquely express membrane IgT while lacking membrane IgD. In addition to playing a key role in adaptive mucosal immune responses, we have also shown an involvement of IgT+ B cells in innate immunity as they possess a high phagocytic and microbicidal capacity. To understand further the roles of these cells in innate immunity, we performed the first comparative transcriptome analysis on FACS-sorted IgT+ and IgM+ B cells. To our surprise the gene that showed the highest differential expression between these two B cell subsets was perforin, a molecule that is not typically associated with B cells. The results obtained by transcriptome were expanded by further RT-PCR analysis confirming that unlike IgM+ B cells, IgT+ B cells expressed high transcript levels of several perforin isoforms, including, prf1-like-B, prf1-like-C and prf1-like-D. We also confirmed the unique expression of these perforin genes in IgT+ B cell by single cell transcriptome analysis. Moreover, we produced antibodies against these perforin molecules and demonstrated by immunohistochemistry the presence of several of these perforin isoforms in IgT+ B cells. Since perforin is a cytolytic protein that forms pores on the cell membrane of target cells, we hypothesized that IgT+ B cells could possess cytotoxic activity similar to that of other perforin-expressing cells, including CD8+ T cells and NK cells. To confirm this hypothesis, we tested the potential cytotoxic capacity of IgT+ B cells towards several mammalian cell lines, such as HL-60. Our results show that the killing activity of IgT+ B cells was significantly greater than that of IgM+ B cells. These data demonstrate a previously unrecognized new function for IgT+ B and vertebrate B cells in immunity.