Decreased Dipeptidyl Peptidase IV Enzyme Activity of Plasma Soluble CD26 and Its Inverse Correlation with HIV-1 RNA in HIV-1 Infected Individuals

Human plasma contains soluble CD26/dipeptidyl peptidase IV (sCD26/DPPIV) although its physiological significance remains unclear. To determine whether the plasma sCD26 levels have clinical relevance in HIV-1 infected individuals, the concentration and DPPIV enzyme activity of plasma sCD26 were measured. While there is no significant difference between the plasma levels of sCD26 in 90 HIV-1 infected individuals and in 79 uninfected controls, specific DPPIV enzyme activity of sCD26 was significantly decreased HIV-1 infected individuals (P < 0.0001). Specific DPPIV enzyme activity was correlated with the levels of CD4+ T cells (r = 0.247; P < 0.02), CD8+ T cells (r = 0.236; P < 0.03), and adenosine deaminase (r = 0.227; P < 0.05) and had an inverse correlation with HIV-1 RNA (Spearman's r = 0.474; P = 0.0012). Furthermore, recombinant sCD26 enhanced the in vitro PPD-induced response of lymphocytes from HIV-1 infected individuals with decreased specific DPPIV enzyme activity. These results suggest that the specific DPPIV enzyme activity of plasma sCD26 may contribute to the immunopathogenesis of HIV infection.