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

Abstract

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 HAMITSP. 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 HAMITSP were 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 HAMITSP 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.