HTLV-I specific IFN-γ+ CD8+ lymphocytes correlate with the proviral load in peripheral blood of infected individuals

Abstract

Human T lymphotropic virus type I (HTLV-I)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) is an inflammatory neurological disease caused by HTLV-I infection. It has been shown that HAM/TSP patients have high proviral loads and an extraordinarily high frequency of circulating CD8+ cytotoxic T lymphocytes specific for HTLV-I in their peripheral blood when compared to asymptomatic HTLV-I carriers (AC). We have previously described an intracellular cytokine detection assay, in which interferon-γ (IFN-γ)+ CD8+ lymphocytes are specific for HTLV-I in infected individuals. Here, we have established a competitive polymerase chain reaction assay to measure the proviral load of patients and investigate a potential relationship between proviral load and virus-specific CD8+ lymphocytes. Genomic DNA was extracted from peripheral blood lymphocytes (PBL) from eight HAM/TSP patients and seven AC for the measurement of HTLV-I measuring proviral loads. The same PBL were analyzed for intracellular IFN-γ expression by flow cytometry. In the HAM/TSP patients and AC, the average proviral loads were 34,482 and 9784 copy/μg DNA ( P=0.021), and the average of IFN-γ+ CD8+ lymphocytes in total PBL were 1.47 and 0.08% ( P=0.001), respectively. It was confirmed that HAM/TSP patients have both high proviral loads and increased HTLV-I-specific CD8+ lymphocytes. Furthermore, we found a positive correlation between both factors in the patients with HAM/TSP ( P=0.044) but not in the AC ( P=0.508). These findings suggest that the high number of HTLV-I-specific lymphocytes may result from the increased proviral load in HAM/TSP patients.