Soluble Fas in serum of patients with HIV/AIDS.

To the Editor: In HIV infection, the mechanism of destruction of the CD41 T cells is unknown. Apoptosis may play an important role in the pathogenesis of HIV. One apoptotic pathway is mediated through the Fas-Fas ligand pathway. Soluble Fas (sFas) in serum is thought to act as an inhibitor of Fas-Fas ligand binding and to block Fas-mediated apoptosis (1 ). We studied the role of sFas as a marker for CD4 cell destruction. Sera were obtained from 60 HIV/ AIDS patients in Chiang Mai, Thailand and stored at 220 °C until use. Serum sFas was measured by ELISA (Medical & Biological Laboratories) according to the manufacturer’s instructions (2 ). Briefly, serum or calibrator was incubated in wells coated with anti-Fas polyclonal antibody. After washing, a peroxidase-conjugated anti-Fas monoclonal antibody was added in each microwell and incubated. After another washing, the peroxidase substrate was added. After incubation, acid was added to each well to stop the enzymatic reaction and to stabilize the developed color. The assay is linear between 0.5 and 2.0 mg/L, and the detection limit is 0.5 mg/L. Absolute CD41 T-lymphocyte counts were obtained on EDTA blood (Coulter Manual CD4 Count Kit). Briefly, blood was combined with MY4 Cyto-Spheres Monocyte Blocking Reagent, and then CD4 Cyto-Sphere reagent was added. An aliquot of the mixture was added to a lysing reagent to lyse the erythrocytes, and crystal violet was used to stain the nuclear material of the leukocytes. The lymphocytes coated with CD4-coated latex spheres were counted in a hemocytometer chamber. Complete blood counts were obtained with an automated cell counter (Hemacell, DATA Cell 16; Hycel). The sFas concentration (mean 6 2 SD) in HIV/AIDS patients was not statistically different from reference values (1.22 6 0.58 vs 0.93 6 0.6 mg/L; P .0.05) and did not correlate with CD4 and absolute lymphocyte number (Table 1). sFas could block apoptosis induced by the Fas ligand in vitro. An increased serum concentration of sFas may be associated with autoimmune-like conditions, (e.g., angioimmunoblastic T-cell lymphoma and systemic lupus erythematosus), adult T-cell leukemia, B-nonHodgkin lymphoma, bladder cancer, hepatocellular cancer, graft-vs-host disease, multiple sclerosis, Graves disease, and AIDS (3–13). The increase in serum sFas does not directly cause autoimmune disease because some healthy elderly individuals had high concentrations of sFas. sFas was correlated with soluble interleukin-2 receptor as well as with cells expressing membrane Fas. Healthy cells undergo apoptosis as part of the normal process of development and maintenance of complex tissues. In HIV/AIDS patients, Casella and Finkel (1 ) in 1997 proposed one major pathway of apoptosis that is mediated through the tumor necrosis family receptor Fas. The Tat protein of HIV-1-infected cells increases Fas ligand expression and may up-regulate Fas ligand on uninfected cells. By contrast, Katsikis et al. (4 ) reported that apoptosis of peripheral blood T cells was Fas-independent in HIV-infected individuals. We conclude that sFas in AIDS patients is not statistically different from reference values and does not correlate with CD4 and absolute lymphocyte counts. sFas detection cannot serve as a marker for CD4 cell destruction.