INTENDED USE

This Human SAA ELISA Kit is to be used for the in vitro quantitative determination of human serum amyloid A (SAA) concentrations in serum, plasma, and other biological fluids. This kit is intended FOR LABORTORY RESEARCH USE ONLY and is not for use in diagnostic or therapeutic procedures.

INTRODUCTION

Serum Amyloid A (SAA) is an acute-phase protein. During acute events, the rise in SAAlevels is the most rapid and intense increase of all acute phase proteins. Cytokines such as IL-1, IL-6, and TNF are considered mediators of SAAprotein synthesis. They stimulate hepatocytes in the liver to produce and release SAAinto the bloodstream. When elevated above normal levels SAAis almost exclusively bound to High Density Lipoproteins (HDL), causing SAAto behave like an apolipoprotein - a protein moiety occurring in plasma lipoprotiens. SAAcirculates at trace levels (1-7 µg/mL) during normal conditions; however 4-6 hours after inflammatory stimulus, SAAlevels can increase by as much as 1000 fold to remarkably elevated levels (500-1000 µg/mL), thus making SAAa sensitive marker. ^1,2

Structural analysis revealed this 104 amino acid (a.a.) polypeptide in its native state has a molecular mass of 12-14 kDa. Serum amyloid A is the serum precursor of amyloid A (AA) protein (8.5 kDa), which is formed when the first 76 amino acids of amyloid A protein are cleaved. The human SAAprotein is polymorphic being made up of a family of several related proteins (SAA₁ to SAA₄). SAA genes are located on chromosome 11p.¹ SAA₁ and SAA₂ are similar genes, which differ by 7 amino acids or more, and encode acute-phase SAAs. SAA₃ appears to be a pseudogene and is substantially different from the others. SAA₄ does not vary significantly during the acute phase response and is an isoform that is present on HDL during homeostasis.^3,4 Each of the acute phase proteins have a unique function in modulating host immune responses but the role of SAA remains unclear. It is known that HDL inhibits SAA"s function. This suggests that SAA needs to be released from HDL complexes in order to become active.⁵ It was reported that SAA may have an important pro-inflammatory and immunostimulating role by recruiting neutrophils, monocytes, and T-lymphocytes into inflammatory lesions.^5,6 As a result of SAA"s association with HDL, a role in cholesterol metabolism has been proposed. SAA, after dissociation from HDL, may play a role in cholesterol transport at local tissues sites during inflammation by binding cholesterol.^2,7

High levels of SAAcan be seen in patients with acute and chronic inflammation. Secondary amyloidosis may develop as a result prolonged or repeated inflammatory conditions in which SAAlevels remain elevated. This progressive, fatal condition is characterized by a gradual loss of organ function, in which fibrils are deposited in peripheral tissues and major organs. The fibrils are caused by the incomplete degradation of SAAin which the AA fragment (8.5 kDa) from the original SAAprotein has been enzymatically cleaved. Measuring SAAlevels in these patients may be a useful indicator of degree of inflammation and response to therapy. Inflammatory disorders such as rheumatoid arthritis, juvenile arthritis, ankylosing spondylitis, familial mediterranean fever, progressive sclerosis as well as chronic infections such as tuberculosis and osteomyelitis are predisposed to developing amyloidosis.^8,9 Measuring SAA levels is also significant in determining pulmonary inflammation in patients with cystic fibrosis,¹⁰ diagnosing and predicting renal allograft rejection,¹¹ determining anti-microbial therapy response in urinary tract infections,¹² opportunistic infections in AIDS,¹³ inflammation in acute viral infections,¹⁴ biocompatiblility of hemodialysis,¹⁵ tissue damage in post-acute myocardial infarction, ¹⁷ and the outcome in severe unstable angina.¹⁶ Also, a differential diagnosis of inflammatory disease may be employed by measuring SAA levels. Acute viral infections may be distinguished from bacterial infections by determining SAA levels.^14-17 It may be useful to confirm diagnosis of acute viral diseases if SAA is assayed at the same time as C-reactive protein, which is a useful inflammatory marker for bacterial infections and does not rise during viral disease.¹⁶

This SAA ELISA is a 2.5-hour solid phase immunoassay readily applicable to measure SAA in serum, plasma, and other biological fluids in the range of 0 to 16mg/mL. It showed no cross reactivity with other cytokines tested. This SAA ELISA is expected to be effectively used for further investigations into the relationship between SAA and the various conditions mentioned.