Measurement of serum amyloid A4 (SAA₄): Its constitutive presence in serum

Abstract

Newly described human serum amyloid A4 (SAA₄) was measured in serum by an enzyme-linked immunosorbent assay using anti-SAA4 monoclonal antibody and recombinant human SAA₄ as the assay standard. Interference by elevated acute phase SAA (aSAA) was abolished by the addition of rabbit anti-human aSAA antiserum prior to the addition ofanti-SAA₄ to the test samples. Normal levels of SAA₄ ranged between 80–140 mg/L, substantially higher than those ofaSAA. No statistically significant difference in SAA₄ levels between normal subjects and patients with Mycoplasma pneumonia was seen, indicating that SAA4 does not behave as an acute phase reactant. Low SAA₄ levels were found in some patients with high aSAA, although no significant relationship between SAA₄ and aSAA was apparent. The constitutive presence of SAA₄ in serum suggests a physiologic function different from that ofaSAA.

Key Words:

• SERUM AMYLOID A
• SAA_e MONOCLONAL ANTIBODY
• RECOMBINANT PROTEIN
• ENZYME-UNKED IMMUNOSORBENT ASSAY
• ACUTE PHASE REACTANT