Comparative studies of decay‐accelerating factor and HLA‐DR within the CD8‐brightly positive population

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Abstract
Decay‐accelerating factor (DAF) is a membrane protein that inhibits C3 convertase activity of autologous complement at the cell surface. We found that DAF+ cells and DAF− (DAFlow, if any) cells are clearly separated from each other among CD8‐brightly positive (CD8bright) cells. Using three‐color fluorescence flow cytometry, we found that whereas the CD8brightDAF− population express HLA‐DR (class II major histocompatibility complex antigens, and an activated T cell marker), the CD8brightDAF+ population does not. Therefore, among the CD8bright T cells, DAF and HLA‐DR are mutually exclusive. In addition, the CD8brightDAF+ population proliferates in the presence of recombinant interleu‐kin 2 (rIL2) while the CD8brightDAF− population does not. After a 4‐day cultivation of peripheral blood lymphocytes in the presence of rIL2, expression of HLA‐DR increased in the CD8brightDAF− population and expression of IL 2Rp55 (α chain, the receptor for IL2, and a marker of T cell activation) occurred in the CD8brightDAF+ population. Furthermore, C3 deposition occurred in the CD8brightHLA‐DR+ population which lacks DAF when lymphocytes, that had been cultured for 3 days in the presence of rIL2, were incubated with fresh autologous serum. This result suggests that the absence of DAF on CD8brightHLA‐DR+ T cells might play a role in permitting complement reaction on the cells in vivo and may be related to the regulation of T cell activation.