Presence of HTLV‐I proviral DNA in central nervous system of patients with HTLV‐I–associated myelopathy

The polymerase chain reaction (PCR) method was used to determine the presence and amount of human T lymphotropic virus type I (HTLV‐I) proviral DNA in central nervous system (CNS) tissue obtained at autopsy from 6 patients with HTLV‐I–associated myelopathy (HAM)/tropical spastic paraparesis (TSP), 1 patient with adult T‐cell leukemia (ATL) and CNS infiltration of leukemic cells, and 9 control subjects with other neurological disorders. HTLV‐I pX and env but not pol DNA were detected in CNS tissue from 5 of 6 patients with HAM/TSP. The ATL samples were positive for pX, env, and pol DNA by PCR. None of the control samples was consistently positive for HTLV‐I by PCR, but all showed positive bands on β‐globin PCR. Quantitative PCR combined with histological studies showed no correlation between HTLV‐I proviral DNA amounts and extent of perivascular mononuclear cell infiltration in the HAM/TSP CNS. Also, the amounts of pX and probably env DNA were greater in the HAM/TSP samples than in the ATL sample, although the extent of mononuclear cell infiltration was far less in the HAM/TSP samples than in the ATL sample. Therefore, in addition to infiltrating mononuclear cells, constituent cells of the CNS may harbor the HTLV‐I genome, at least in the pX and env regions, in patients with HAM/TSP.