α2-Macroglobulin (α2-M) ELISA

Alpha-2-Macroglobulin (α2M) is one of the biggest plasma proteins, with a molecular
weight of 650–900kDa, depending on the degree of glycosylation. It consists of
4 identical subunits. α2M inhibits all known classes of endopeptidases by binding
them and thereby blocking their active sites. The α2M-endopeptidase complex is
then cleared rapidly from the circulation by the endocytotic proteinase clearance
pathway. α2M also binds, transports and regulates many other molecules like defensins,
myelin basic protein, and a host of other cytokines, growth factors, and hormones.
Measuring urinary proteins allows the diagnosis of proteinuria, which is defined as
150mg protein/day. Proteinuria can be divided into prerenal, renal (glomerular or
tubular), and postrenal proteinuria depending on the localisation of the kidney damage.
Differential diagnosis can be achieved by measuring certain marker proteins of
different molecular weights. Very large proteins, such as α2M, are completely restricted
from glomerular filtration in the kidneys. Thus, detecting α2M in urine is evidence
of postrenal damage, when unfiltered serum proteins leak into the urine. Causes of
postrenal damage are inflammation or hematuria as a consequence of renal stones
or carcinomas.