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

The effects of alpha 1-antitrypsin (alpha 1-AT), alpha 1-acid glycoprotein (alpha 1-AGP), and haptoglobin (Hp), the main constituents of alpha-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, alpha 1-AT and alpha 1-AGP had inhibitory effects on NK activity for "fast target" K562 cells. The alpha 1-AT preparations having the same protein concentration and a different trypsin inhibitory capacity (TIC) had an equal effect. Although alpha 1-AT and alpha 1-AGP equally reduced the NK activity, the mechanism involved in the reduction differed, in that the effect of alpha 1-AT directed toward NK cells reduced their binding capacity with the target cells. alpha 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.