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

The effects of α₁-antitrypsin (α₁,-AT), α₁,-acid glycoprotein (α₁AGP), and haptoglobin (Hp), the main constituents of α-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, α₁,-AT and α₁AGP had inhibitory effects on NK activity for "fast target" K562 cells. The α,-AT preparations having the same protein concentration and a different trypsin inhibitory capacity (TIC) had an equal effect. Although α₁AT and α₁,-AGP equally reduced the NK activity, the mechanism involved in the reduction differed, in that the effect of α₁,-AT directed toward NK cells reduced their binding capacity with the target cells, α₁,-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.