Improved hepatic and pancreatic localisation of the equine alpha-1-proteinase inhibitor family of serpins using an antigen enhancement technique and a monoclonal antibody

Equine alpha-1-proteinase inhibitor (API) consists of three, occasionally f our, serum glycoproteins. This study investigated the immunohistochemical l ocalisation of equine API in paraformaldehyde fixed, paraffin embedded equi ne tissue samples of liver, lung, stomach, pancreas, jejunum and colon in f ive horses using affinity purified sheep polyclonal and protein A purified mouse monoclonal antibodies, whose specificities were verified by Western b lotting. Exposing tissue sections to boiling citrate buffer greatly enhance d antigen recovery and improved immunostaining with both antibodies, result ing in discovery of novel tissue distribution patterns for the horse. In th e horses studied, all hepatocytes showed some degree of cytoplasmic stainin g, many having perinuclear intense granular inclusions. This finding is con trary to findings in human studies where hepatocytes of Pi MM phenotype hav e proven difficult to stain for human API, despite evidence at the molecula r level suggesting hepatocytes as the major source of serum API. This discr epancy may be due to the use of different tissue fixation and antigen recov ery techniques. Tn all other tissues examined, the distribution of equine A pr was similar to human studies.