Human foamy virus genome in the thymus of myasthenia gravis patients.

The etiological relationship of human foamy virus (HFV), which is a spumaretrovirus, with human diseases is not clear. We analyzed thymus specimens from four patients with myasthenia gravis for the presence of HFV proviral genome by polymerase chain reaction (PCR). The results showed the presence of both 257 base pair (bp) and 299 bp DNA fragments representing a part of gag and bel-2 sequences, respectively, in all four thymuses. Their specificity was confirmed by Southern blot hybridization with the corresponding probes. This was also confirmed by sequence analysis, although there were some point mutations. We confirmed the presence of gag related sequence, a 1353 bp Xba I-cleaved DNA fragment in all four thymus samples, a 693 bp fragment in two (#3 and #4) and a 4300 bp Hind III-cleaved DNA fragment in another two (#1 and #4), indicating possible chromosomal integration of the HFV partial genome. To our knowledge, this is the first report on the presence of HFV genome in thymus tissues of myasthenia gravis patients. Our efforts to isolate the infectious HFV by cultivation of the tissues were not successful. Low titers of neutralizing antibody were detected in all four patients' serum samples. The possible role of the HFV in this autoimmune disease needs further investigation.