Decreased expression of the membrane inhibitor of complement-mediated cytolysis CD59 on T-lymphocytes of HIV-infected patients

Objective: To study the expression of the membrane inhibitor of complement-mediated cytolysis, CD59, on peripheral blood mononuclear cells (PBMC) from HIV-infected individuals. Methods: CD59 membrane expression was investigated by double immunofluorescent staining on purified PBMC from HIV-infected patients and seronegative controls. Results: CD59 expression was decreased on peripheral blood T-lymphocytes from HIV-infected patients. Decreased expression of CD59 antigen did not correlate with clinical stage of disease. Low CD59 expression on T-lymphocytes was mediated by several mechanisms, including (1) decrease in number of CD4+ cells which normally express high amounts of the antigen; (2) relative increase in CD8+ cells, more specifically in CD8+ CD57+ cells expressing a low density of the antigen; (3) loss of or decreased CD59 expression on a subpopulation of CD3+ belonging either to the CD4+ or to the CD8+ subset. Decreased CD59 expression was consistently observed on CD8+ lymphocytes. CD59 expression was normal on patient red blood cells, monocytes and B-lymphocytes. Conclusions: HIV infection is associated with a T-cell-specific defect in CD59 membrane expression. Decreased CD59 expression may result in increased susceptibility of T-lymphocytes from HIV-infected patients to complement-mediated lysis.