[The nervous system involvement in human retroviral infection]

Human T-lymphotropic virus type I (HTLV-I) is a pathogenic retrovirus associated with a chronic progressive myelopathy, termed HTLV-I-associated myelopathy (HAM). A chronic inflammatory process has been implicated in HAM by a pathological study, but the exact mechanism still remains to be elucidated. Our quantitative polymerase chain reaction study indicated that the large increase in the HLTV-I proviral DNA in peripheral blood is associated with the development of HAM. The nucleotide sequence analysis of HTLV-I in central nervous system (CNS) tissue of HAM patients revealed that the sequences of HTLV-I genome were heterogenous in all cases, and that the pX-defective mutants were found frequently in the CNS. Thus, HTLV-I exists as quasispecies in vivo, as shown in the case of human immunodeficiency virus. It is possible that the HTLV-I pX microvariants contribute to the neural damage, since the pX gene products are essential for the transactivation of various cellular genes as well as for viral replication.