Abstract
A 14 kilodalton (kDa) serum amyloid A (apoSAA) protein was purified from cow serum. Rabbit antiserum to the 14 kDa apoSAA recognized, in addition to the 14 kDa protein, a 7.5-9.0 kDa protein and a protein having a molecular mass of less than 6.5 kDa (<6.5 kDa protein). The possibility that the two proteins were contaminants was excluded by results showing that the two proteins detected in early stages of purification procedures were not found in the purified 14 kDa apoSAA fraction, as revealed by immunoblot analysis. As in the 14 kDa apoSAA, the 7.5-9.0 kDa protein was localized in the high-density lipoprotein fraction, while the <6.5 kDa protein was in the low-density lipoprotein fraction. In calves with pneumonia induced by inoculation to the lungs of Pasteurella haemolitica, the serum concentration of the 14 kDa apoSAA was increased, whereas those of the 7.5-9.0 kDa and the <6.5 kDa proteins were conversely decreased. The time-course study indicated that the increase in concentration of the 14 kDa apoSAA and decrease in that of the <6.5 kDa protein occurred almost simultaneously. These results suggest that the 14 kDa apoSAA and the immunologically related 7.5-9.0 kDa and <6.5 kDa proteins act as positive and negative acute phase reactants, respectively, and also that concentrations of the three proteins are regulated in concert in acute phase plasma.
