Arthritis & Rheumatism, Volume 60,
October 2009 Abstract Supplement

The 2009 ACR/ARHP Annual Scientific Meeting
Philadelphia October 16-21, 2009.


Allelic Imbalance of BLK Detected in CD4 T Cells Suggesting That BLK Acts Via T Cell Pathways in Autoimmune Pathogenesis

Olsson1,  Lina M., Graham2,  Robert R., Gregersen1,  Peter K.

Feinstein Institute for Medical Research, Manhasset, NY
Genentech, Inc., South San Francisco, CA

Purpose:

The intracellular tyrosine kinase, B-lymphocyte kinase (BLK) is associated with both Rheumatoid Arthritis and Systemic Lupus Erythematosus. Three associated SNP variants in BLK are located in the same haplotype covering the 5'UTR/promoter region and upstream sequences. Studies in B cell lines show that the RA associated allele of the upstream SNP rs13277113 is associated with a lower mRNA expression of BLK. The SNP marker rs922483 in the 5'UTR of BLK is in high LD with all the associated variants (r2= 0.8–0.9). We wished to determine the effect of the Blk risk haplotype on expression in freshly isolated and separated peripheral blood cells.

Method:

Transfection experiments suggest that rs922483 is a causative variant for Blk expression differences in B cell lines. Its location in the mature BLK transcript permitted us to use this variant to directly investigate allele specific expression in freshly isolated peripheral blood cells in heterozygous individuals. We separated B cells, CD4+ and CD8+T cells, granulocytes, monocytes, macrophages and dendritic cells in normal subjects with defined BLK genotype.

Results:

Using TaqMan assays, we documented high Blk expression in B cells, with decreased Blk after activation with anti IgM and/or CD40. T cells expressed lower levels of Blk and Blk transcript was extremely low in most other cells types. Using a sensitive pyrosequencing assay for allelic imbalance we have made two unexpected observations. First, both resting and activated B cells showed no evidence of allelic imbalance, in contrast to published reports in B cell lines. Secondly, prominent allelic imbalance was present in CD4+ T cells in 5/6 individuals, with lesser degrees of allelic imbalance in CD8+ T cells. Compared to the DNA reference allele ratio (A/G) of 0.4 ± 0.03, the ratio in CD4+ T cells was lower and ranges between 0.1 and 0.3 in the 5 individuals showing allelic expression differences.

Conclusion:

These data suggest that the causative Blk allele may play a role in disease pathogenesis by its action in T cells as opposed to, or in addition to, B cells. The contrasting data in fresh B cells compared with B cell lines suggests that if Blk plays a role in autoimmune pathogenesis in B cells, it may be in particular subsets of B cells. Future studies will investigate the role of Blk alleles in regulating expression in specific B cell subsets.

To cite this abstract, please use the following information:
Olsson, Lina M., Graham, Robert R., Gregersen, Peter K.; Allelic Imbalance of BLK Detected in CD4 T Cells Suggesting That BLK Acts Via T Cell Pathways in Autoimmune Pathogenesis [abstract]. Arthritis Rheum 2009;60 Suppl 10 :1087
DOI: 10.1002/art.26163

Abstract Supplement

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