Elevated levels of iC3b and C4d, but not Bb, complement fragments from plasma of persons infected with human T cell leukemia virus (HTLV) with HTLV-I-associated myelopathy/tropical spastic paraparesis.

Plasma levels of complement (C) fragments iC3b, C4d, and Bb from human T cell leukemia virus (HTLV)-positive subjects with HTLV-I-associated myelopathy (HAM)/tropical spastic paraparesis (TSP) were analyzed by EIA. Both iC3b and C4d levels were significantly elevated in persons with HAM/TSP. These levels were similar to those in patients with human immunodeficiency virus (HIV) infection or rheumatoid arthritis (RA), who are known to have increased C fragments. Bb levels in persons with HAM/TSP wer unaffected, suggesting that C activation occurred only via the classical pathway. This differed from findings in HIV-infected or RA patients, who had elevated levels of Bb. The results showed an increase in C activation in persons with HAM/TSP and activation via the classical pathway, likely mediated by virus or immune complexes. It is possible that the C activation observed in these subjects contributed to the inflammatory pathogenesis of HAM/TSP.