MEASUREMENT OF SERUM AMYLOID A(4) (SAA(4)) - ITS CONSTITUTIVE PRESENCE IN SERUM

Newly described human serum amyloid A(4) (SAA(4)) was measured in seru m by an enzyme-linked immunosorbent assay using anti-SAA(4) monoclonal antibody and recombinant human SAA(4) as the assay standard. Interfer ence by elevated acute phase SAA (aSAA) was abolished by the addition of rabbit anti-human aSAA antiserum prior to the addition of anti-SAA( 4) to the test samples. Normal levels of SAA(4) ranged between 80-140 mg/L, substantially higher than those of aSAA. No statistically signif icant difference in SAA(4) levels between normal subjects and patients with Mycoplasma pneumonia was seen, indicating that SAA(4) does not b ehave as an acute phase reactant. Low SAA(4) levels were found in some patients with high aSAA, although no significant relationship between SAA(4) and aSAA was apparent. The constitutive presence of SAA(4) in serum suggests a physiologic function different from that of aSAA.