Influence of acute-phase proteins on the activity of natural killer cells

The effects of₁-antitrypsin (₁,-AT),₁,-acid glycoprotein (₁AGP), and haptoglobin (Hp), the main constituents of-globulin and which belong to acute phase proteins, on NK activity were examined using K562 cells as the NK target cells. Among the three proteins,₁,-AT and₁AGP had inhibitory effects on NK activity for fast target K562 cells. The,-AT preparations having the same protein concentration and a different trypsin inhibitory capacity (TIC) had an equal effect. Although₁AT and₁,-AGP equally reduced the NK activity, the mechanism involved in the reduction differed, in that the effect of₁,-AT directed toward NK cells reduced their binding capacity with the target cells,₁,-AGP probably interacts with a cytotoxic factor secreted from NK cells following effector-target interaction. These studies suggest that each of the acute-phase proteins, which increase following inflammation, inhibits NK cell function by two distinct mechanisms.