Development and use of two Xenopus laevis spleen stromal cell lines to study the role of splenic stromal cells in anuran immune processes

Abstract

The spleen is an important immune organ in adult Xenopus laevis, supporting the differentiation of B cells and acting as the main peripheral lymphoid organ. Key to these processes are the supporting non-hematopoietic cells, or stromal cells, within the spleen tissue. Despite the importance of the spleen to frog immunity, few frog cell lines originating from spleen tissue have been reported. In this study, we report on the establishment and characterization of two cell lines originating from X. laevis spleen tissue, Xela S5F and Xela S5E. Morphological observations and gene expression profiling suggest that Xela S5F is fibroblast-like and Xela S5E is epithelial-like. Both cell lines express transcripts corresponding to a variety of hematopoietic growth factors, suggesting their potential utility as a feeder cell line to support ex vivo myelopoietic cell differentiation. Xela S5F and Xela S5E produce transcripts for a diversity of pattern recognition receptors including toll-like receptors, scavenger receptors, and cytosolic nucleic acid sensors, suggesting anuran spleen stromal cells may be important cellular sensors of pathogens filtered through the spleen. This idea is supported by the increase in transcript levels for antiviral and proinflammatory genes in both cell lines in response to treatment with the commercially available toll-like receptor ligands, flagellin and poly(I:C). However, despite the ability to sense extracellular synthetic analogues of viral nucleic acids [i.e. poly(I:C)] and susceptibility and permissibility of both cell lines to frog virus 3 (FV3), a large double-stranded DNA virus that infects amphibians, neither cell line upregulates key antiviral or proinflammatory transcripts when challenged with FV3. The establishment of Xela S5F and S5E cell lines expands the current X. laevis invitrome and provides new in vitro cell model systems to investigate the role of splenic stromal cells in anuran immune functions.

Keywords: Cell lines; Frog Virus 3; Frogs; Splenic stromal cells; Xela S5E; Xela S5F.