Abstract
We have investigated the isotypic and IgG subclass profile of the antibody response to HTLV-I structural proteins ( gag and env) in patients with HTLV-I-associated myelopathy (HAM; n = 20), adult T-cell leukemia (ATL; n = 15), and HTLV-I-positive asymptomatic carriers (ASY; n = 21). IgG, IgM, and IgA were the predominant antibody responses in all HTLV-I-infected individuals; minimal IgE response was detectable in the HAM and ATL groups. Among the IgG subclasses, IgG 1 was the most predominant antibody detected in responses to HTLV-I antigens, followed by IgG 3 and IgG 2; IgG 4 could not be detected in any patient group. Levels of both IgG 1 and IgG 3 were significantly higher in patients with HAM, when compared to ATL and ASY ( P < 0.01 for both comparisons). In addition, Ig isotypes and IgG subclass antibody in patient sera reactive with purified viral proteins and several immunodominant epitopes, represented by synthetic peptides, Gag-1a 102-117, Env-1 191-214, Env-5 212-257, and recombinant proteins, MTA-1 162-209 and r21e 303-410, were examined to delineate specific epitopes responsible for inducing the host immune responses of each isotype and subclass to the structural proteins of HTLV-I. IgG, IgM, and IgA responses were directed against both the gag and env gene products. Among IgG subclasses, the IgG 1 and IgG 3 responses were directed against both the gag (p53, p24, p19, and Gag-1a) and env (recombinant MTA-1, r21e, and synthetic Env-1, Env-5) proteins; IgG 2 responses were mainly restricted to gag proteins. The frequency profile of HTLV-I-specific antigen recognition in all four IgG subclasses were similar in all of the clinical groups. These results further define the fine specificity of anti-HTLV-I immune reaction for understanding the mechanism of pathogenesis in these individuals and suggest that factors other than the humoral immune responses may be associated with the clinical manifestation of the disease.
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