Tumor Necrosis Factor-Alpha and Interleukin-6 Promoter Gene Polymorphisms in Acquired Bone Marrow Failure Syndromes.

Some acquired aplastic anemia (AA) results from immune mediated destruction of the hematopoetic stem cells. Immunosuppressive therapy is successful in majority of AA patients and substantial laboratory data are consistent with an immune pathophysiology. Substantial research has implicated differences in cytokine gene expression profiles and polymorphisms in the genes controlling cytokine expression in other autoimmune diseases such as lupus erythematosus and rheumatoid arthritis. Interlukin-6 (IL-6) and tumor necrosis alpha (TNF-α) are two potent pro-inflammatory cytokines that have implicated in a variety of immune-mediated conditions. TNF-α results in Fas expression and apoptosis of in progenitor cells and the TNF-alpha −308 allele was significantly associated with SLE in Caucasians. Levels both IL-6 and TNF-α have been reported elevated in AA patients. In the promoter region of the IL-6 gene, at position −174, exists a single nucleotide polymorphism (G/C) in close proximity to a glucocorticoid-responsive element; patients homozygous for the G allele have circulating IL-6 concentrations close to twice as high as those homozygous for the C allele. The TNF-α gene, located in the class III region of the major histocompatibility complex (MHC), has a polymorphism at position −308, TNF2, where the presence of adenine instead of guanine is associated with higher cytokine production. In our study, we characterized the IL-6/−174 and the TNF-α/−308 polymorphisms in patients with acquired bone marrow failure syndromes to assess if the higher production genotypes were more prevalent that in established controls. We identified seventy-three patients (age range 3–84) treated at our institution for AA. Following an established protocol for the identification of single nucleotide polymorphisms, genomic DNA was amplified with primers designed for the promoter regions of the IL-6 and TNF-α genes where intentional mismatches were inserted at 1–3 nucleotide positions to incorporate a restriction site for endonucleases. The amplicons were digested with four restriction endonucleases (BlsI, BsaBI, EcoNI, RsaI) then analyzed by electrophoresis in 3% agarose gels. The resulting fragments allowed for the identification and confirmation of the specific nucleotide polymorphism at the 174 and 308 position of the IL-6 and TNF-α promoter, respectively. The frequency of the high cytokine producing genotypes in the cohort was compared to established controls and the statistical significance determined by the two-tailed Fishers exact test. The GG genotype of the IL-6/−174 polymorphism was present in 32 of 73 (44%) of affected patients versus 80 of 250 (32%) historical controls of the control population (p =0.0698) while the AA genotype of the TNF-α/−308 polymorphism was found in 8 of 73 AA patients (11%) and in only 9 of 354 historical controls (2.5%) (p= 0.0034). Three of 73 AA patients had both gene polymophisms p<0.0001. Two patients’ BM was cultured and ELISA performed for TNF-α as part of a larger study, which included 20 normal controls and 30 patients with marrow failure; both of these patients demonstrated significant elevations in TNF-α. In conclusion, we showed that some patients with acquired bone marrow failure have cytokine gene polymophisms which are linked to high production of pro-inflammatory cytokines, particularly TNF-α.