Immunohistochemical demonstration of inter-alpha-trypsin inhibitor light chain (bikunin) in human mast cells

We recently reported that the rat mast cell proteinase inhibitor trypstatin is genetically identical with the second half of inter-alpha-trypsin inhib itor light chain (ITI-LC), also known as bikunin or urinary trypsin inhibit or (UTI). In this study, therefore, immunoreactivities of mast cells of var ious human tissues were examined with three antibodies, anti-human ITI-LC, anti-ITI, which recognizes mainly heavy chains or the sugar moiety of ITI, and anti-a l-microglobulin (alpha 1mG). ITI-LC immunoreactivity was strongl y found in mast cells in the connective tissues of various organs except fo r those of the propria mucosae of small intestine. Neither anti-In antibody nor anti-alpha 1mG antibody reacted with mast cells in various tissues. By reverse transcription-polymerase chain reaction (RT-PCR) analysis, alpha 1 mG/ITI-LC mRNA was not detected in the skin and tongue, and only weakly in small intestine, although ITI-LC immunoreactivity was strongly detected in these tissues. Furthermore, the mRNA was not expressed in cultured human ma st cells. These results suggest that ITI-LC protein is stored in the granul es of human connective tissue mast cells, though is not produced by them.