Development and validation of an ELISA for the quantification of bovine ITIH4 in serum and milk

Inter alpha trypsin inhibitor heavy chain 4 (ITIH4) is a serum protein belonging to the Inter alpha trypsin inhibitor (ITI) family, which was previously characterized by our group as a new APP in cattle. This protein was firstly described in pigs where is known to be a major acute phase protein, also denominated Pig-MAP. Increases of ITIH4 of up to 12 times the pre-infection values were previously reported in the serum of heifers with experimentally induced summer mastitis. ITIH4 was detected in the milk of cows with mastitis by western blot, but the method previously used to quantify this protein, radial immunodiffusion, was not sensitive enough to quantify it in milk samples. In this study we developed an ELISA method which allows the quantification of bovine ITIH4 in serum and milk samples. Previously developed antibodies were used to perform the assay, including anti bovine ITIH4 polyclonal antibodies and a monoclonal antibody against pig ITIH4 that also recognizes the bovine homologous protein. The ELISA developed showed an adequate precision, with inter and intra- assay coefficients of variation lower than 10% for serum and milk samples. The assay keeps linearity under dilution for both serum and milk samples. A good agreement was observed between the values measured by ELISA and radial immunodiffusion in serum samples.