Seq'ing Answers to Equine Common Variable ImmunoDeficiency

Our laboratory investigates a late-onset immunodeficiency in horses called Common Variable ImmunoDeficiency (CVID).  CVID is characterized by recurrent bacterial infections, decreased serum IgM and IgG concentrations, and depletion of peripheral B cells.  We have determined that the loss of B cells is due to a failure of differentiation in the bone marrow.  Transcriptome sequencing was undertaken to assess the expression of genes and transcription factors known to be essential for B cell differentiation, and simultaneously obtain a comprehensive view of gene expression in the bone marrow.  Analysis of bone marrow mRNA expression from CVID horses revealed a significant decrease in E2A (p < 0.05) and a marked decrease in PAX5 (p < 0.01) expressions in comparison to healthy horses.  E2A and PAX5 are transcription factors essential to successful B cell differentiation, and are indicative of specific B cell stages.  Subsequently, MethylSeq was performed to compare the genome-wide methylation status between CVID and healthy horses.  Differential methylation of the PAX5 gene body was identified in the bone marrow of CVID horses.  These results imply that the loss of B cell hematopoiesis in CVID horses occurs at the transition from pre-pro B cells to pro-B cells, and may be due to a difference in the epigenetic status of a key B cell gene that leads to gene silencing.  Finally, although CVID-affected horses are of various breeds and geographic regions, a genome-wide association study has been initiated to determine whether genetic markers are associated with susceptibility to CVID.