Neurologic diseases associated with human T-cell lymphotropic virus ty
pe I (HTLV-T) infection have a clinical spectrum that includes myelopa
thy (HTLV-I-associated myelopathy/tropical spastic paraparesis, HAM/TS
P) as the central manifestation. Many clinical signs of involvement ou
tside the central nervous system (CNS) have been described in some pat
ients with HAM/TSP and have triggered and advanced the discovery of so
me HTLV-I-associated concepts In HTLV-I-infected individuals without s
igns of CNS involvement. Most of these HTLV-I-associated diseases exhi
bit common viroimmunologic characteristics that include a distribution
al bias of HTLV-I activation between the blood flow and the affected l
esions and accumulated cellular immune responses in the lesions. These
facts suggest that the vulnerable tissue(s) in some HTLV-I-infected i
ndividuals may not be defined by an exclusive tissue specificity, but
that common steps df HTLV-I-versus-host interactions may have an impor
tant role in the pathologic process(es) in these diseases. This review
summarizes the recent perspectives of the clinical spectrum and the p
athogenesis of HAM/TSP in Japan. Furthermore, the feasible pathogenic
involvement of cellular interactions between infected cells and respon
ding immunocompetent. cells in the affected tissues is emphasized.