Characterization of a tryptase mRNA expressed in the human basophil cell line KU812

The expression of a tryptic serine protease was detected in the cell line KU812 by Northern blot analysis with an oligonucleotide probe directed against a conserved region present in all of the five presently cloned human mast cell tryptases. PCR primers designed for the amplification of a nearly full-length copy of tryptase mRNAs were used to study the identity of the KU812 tryptase. Ten clones were characterized and all were found to be identical to one of the tryptases previously cloned from a human skin cDNA library. This tryptase has been thought to originate from mast cells of the skin. Two possible explanations may account for the observed identity between the presumed mast cell tryptase and the KU812 tryptase. Firstly, it is possible that the KU812 tryptase is a basophil-specific tryptase which has previously been cloned from a human skin cDNA library containing low levels of cDNA copies derived from basophils in the starting material. Secondly, the KU812 cell line, and possibly normal basophils, express a tryptase which is identical to one of the tryptases expressed in normal skin mast cells. We cannot at present rule out any of the two possibilities, but we favour the second explanation as being the most likely.