A neuropathological study of paraparetic rats injected with HTLV-I-producing T cells.

In order to clarify the pathogenesis of HTLV-I-associated myelopathy or tropical spastic paraparesis (HAM/TSP), we injected HTLV-I-producing rabbit or human T cells intravenously into WKA and F344 rats. Infection was confirmed from increase in the anti-HTLV-I antibody titer and from the presence of HTLV-I proviral DNA. Only WKA rats developed hindlimb paraparesis 78-124 weeks after the injection. Neuropathological examination of 5 rats showed degeneration of the anterolateral and posterior funiculi as well as the peripheral nerves, and this degeneration was characterized by prominent vacuolation and macrophage infiltration. The myelopathy and neuropathy were grossly similar to those in human HAM/TSP. Although pathological changes of the spinal cord were very mild in 2 paretic rats, and similar lesions were found in the spinal cords and peripheral nerves of 2 control WKA rats, the myelopathy, radiculoneuropathy, or both in the paretic rats showed greater severity than in the controls. The contribution of the aging process to the lesions of the spinal cord and peripheral nerve is discussed. It appears possible that HTLV-I may accelerate the aging process and give rise to paraparesis. The precise role of HTLV-I in the pathogenesis of rat paraparesis remains to be elucidated taking the role of the aging process of the spinal cord and peripheral nerve into account.