SERUM HAPTOGLOBIN AS AN INDICATOR OF THE ACUTE-PHASE RESPONSE IN BOVINE RESPIRATORY-DISEASE

The early stages of the host response to infectious agents include a n umber of physiologic changes, collectively known as the acute phase re sponse. The acute phase response is comprised of reactions localized a t the site of infection, as well as the initiation of systemic respons es, which include a rapid increase in the serum concentration of some proteins, known as acute phase proteins (APP). Using polyacrylamide ge l electrophoresis, we detected two APP of approximately 22 and 37 kDa molecular weight in sera obtained from cattle with bovine respiratory disease (BRD), Based on their presence in the sera of sick, but not no rmal animals, the molecular weights, N-terminal amino acid sequence an alysis, and the ability to bind hemoglobin, we identified these protei ns as the a and beta subunits of haptoglobin. The haptoglobin molecule and the alpha subunit were isolated from serum, purified, and used to produce monoclonal and polyclonal antibodies. With these reagents, an enzyme linked immunosorbent assay was developed to measure the concen tration of haptoglobin in bovine serum. Using an experimental model of BRD induced by a sequential challenge of calves with bovine herpesvir us type-1 and Pasteurella haemolytica, we observed a temporal relation ship between the increase in haptoglobin concentration in serum and th e onset of bacterial infection. The haptoglobin concentration ranged f rom undetectable in the serum of most calves prior to challenge, to gr eater than 1 mg ml(-1) in over one-third of the calves at the height o f disease. Furthermore, the concentration of haptoglobin was associate d significantly with other measures of the severity of disease. Togeth er, these results indicate that quantification of acute phase proteins in animals with BRD could be a valuable diagnostic and prognostic aid .