Comparative transcriptome analysis of the transcriptional heterogeneity in different IgM+ cell subsets from peripheral blood of Nile tilapia (Oreochromis niloticus)

In teleost fish, IgM(+) B cells play important roles in innate and adaptive immunity. Different IgM(+) B cells are detected in teleost, named IgM(lo) and IgM(hi) B cell subsets, according to the distinct expression levels of membrane IgM (mIgM). However, the study on the heterogeneity in IgM B cell subsets remains poorly understood. In this study, the comparative transcriptomic profiles of IgM(-), IgM(lo) and IgM(hi) from peripheral blood of Nile tilapia (Oreochromis niloticus) were carried out by using RNA-sequencing technique. A total of 6045 and 5470 differentially expressed genes (DEGs) were detected in IgM(lo) and lgM(hi) cells, respectively, as compared with IgM(-) lymphocytes, whereas 3835 genes were differentially expressed when IgM(lo) compared to IgM(hi) cells. Analysis of the KEGG database indicated that the DEGs were enriched in immune system categories and signaling transduction and interaction in IgM(-) vs IgM(hi), IgM(-) vs IgM(hi) and IgM(lo) vs IgM(hi). Comparatively, in IgM(lo) vs IgM(hi), GO enrichment analysis indicated that the DEGs enriched in nucleic acid binding transcription factor activity. Analysis of crucial transcription factors for B cell differentiation indicated that IgM(lo) and IgM(hi) cell clusters belonged to the different B cell subsets. The data generated in this study may provide insights into understanding the heterogeneity of IgM(+) cells in teleost, and suggest that IgM(+) B cells play a crucial role in innate immunity.