A group from Japan has conducted a retrospective study of 130 patients who underwent stem cell transplantation in an attempt to identify a risk factor for the development of encephalopathy. Although HLA mismatch and unrelated donor status were strongly associated with HHV-6 reactivation (odds ratio of 5.6 and 4.5, respectively) these factors were not associated with HHV-6 encephalopathy, a condition that can often result in permanent neurologic disability and/or death of the patient.
Interestingly, however, the investigators found a remarkably increased level of risk (odds ratio of 31.1) for the development of encephalopathy when transplant occurred with HLA class I allele HLA-B*40:06 in particular. HLA class I alleles have been associated with several autoimmune diseases as well as viral infections, and higher levels of this allele have been reported in patients with HIV compared to healthy controls. The authors speculate that this association may be due to reduced function of cytotoxic T cells. Other associations with this allele include progressive multifocal luekoencephalopathy, ocular Behcet’s disease and Rasmussen syndrome. In addition, Yashiki et al reported that HLA-B*40:06 predisposes patients to adult T cell leukemia (Yashiki 2001).
HLA-B, or human leukocyte antigen-B is part of the major histocompatibility complex (class I, part B), and is a gene that plays an important role in the immune system by providing instructions for making proteins and displaying peptides on the surface of cells to be recognized by the immune system. Once the peptides are recognized, the infected cell can then be destroyed.
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