Acute phase response of serum amyloid A protein and C reactive protein to the common cold and influenza.

C reactive protein (CRP) and serum amyloid A protein (SAA) are sensitive and rapid acute phase reactants, and their measurement for monitoring inflammatory disease and assessing the prognosis in secondary amyloidosis is gaining widespread acceptance. The changes in these proteins in eight subjects suffering from natural colds, 15 subjects with experimentally induced colds (rhinoviruses E1, 3, 9, 14, or 31), and eight with experimentally induced influenza (A/Eng/40/83) were studied. SAA concentration increased in 21 of the 23 subjects with natural or experimental rhinovirus colds (mean increase 95 mg/l); CRP concentration increased in 11 (mean increase 11 mg/l). All subjects with influenza showed pronounced increases in SAA concentrations (mean increase 642 mg/l) while six showed increases in CRP concentration (mean increase 22 mg/l). All these increases were highly significant (p less than 0.001). Asymptomatic excretors of both rhinovirus and influenza virus showed significant increases in SAA concentration (p = 0.015 for rhinovirus and p less than 0.001 for influenza virus) but not in CRP concentration. No changes in SAA or CRP values were seen in 12 volunteers after challenge with saline. These observations suggest that caution is required in the interpretation of estimations of SAA concentration and that it may be too sensitive an acute phase protein for clinical use as its concentration may be raised in both trivial and asymptomatic viral infections.