Quantitative measurement of the novel human plasma protein, IHRP, by sandwich ELISA

Inter-alpha-trypsin inhibitor family heavy chain-related protein (IHRP), which has a sequence similarity to the heavy chains of the inter-alpha-trypsin inhibitor (ITI) family, is a novel glycoprotein found in human plasma, We prepared two clones (1A4 and 6E11) of anti-IHRP mouse monoclonal antibody. Both of them recognized the C-terminal 35-kDa fragment which was produced by plasma kallikrein-digestion of IHRP. We developed a sandwich ELISA for measurement of the plasma IHRP concentration with the monoclonal antibody coated microtiter plate and the anti-N-terminal 57-kDa fragment of IHRP rabbit polyclonal antibody (anti-GP57). We found that the average concentration of IHRP in the plasma of healthy donors was 101,3 +/- 31,8 mug/ml (average +/- S.D.). The IHRP concentration in the plasma of patients with inflammatory disorders was slightly increased (137.5 +/- 40.2 mug/ml: average +/- S.D.). Together with the previous data indicating the induction of the porcine mRNA, which is thought to be the species counterpart of human IHRP mRNA, in the liver after resuscitation from cardiogenic shock, we propose that IHRP is a member of the acute-phase protein family.