Distribution and localization of inter-alpha-trypsin inhibitor and its active component acid-stable proteinase inhibitor: comparative immunohistochemical study.

Inter-alpha-trypsin inhibitor (ITI) is a complex that consists of three components. One of these is the acid-stable proteinase inhibitor (ASPI), which is an acute-phase reactant and a broad-spectrum inhibitor. The tissue distribution of ITI and ASPI were investigated and compared using immunohistochemical methods. ITI immunoreactivity was revealed only in the liver and plasma, while ASPI immunoreactivity was found to be distributed in the brain, liver, kidney, gastrointestinal tract, plasma, and urine. Both immunoreactivities were demonstrated in Kupffer cells of the liver, which is thought to be an ITI-producing organ. From these results, it seems unlikely that ASPI is distributed as a part of the ITI molecule. The residual component of ITI may act as a carrier protein of ASPI, or ASPI in the tissues may be produced independently of ITI.