Serum Proteins
Serum Proteins:
The bloodstream is home to hundreds of different proteins. A smaller subset is used in clinical testing. A common test run in the clinical lab is serum protein electrophoresis (SPEP). This test separates proteins into five different groupings based on electrical charge. The five groups are: albumin, alpha-1, alpha-2, beta, and gamma. The albumin is mostly homogenous but the other four groups (globulins), have a wide variety of proteins that make up each group.
About 50-60% of the total protein is albumin. The remaining four groups named the globulins make up the rest of the protein. When an SPEP is run, qualitative peaks are extrapolated based off of the density of the band on the gel.
Proteins flow based off of surface charge, and all of the serum proteins have a net negative surface charge. Here is a typical normal pattern which shows all five groups as well as the application point of the sample.
Endosmosis:
An important concept in protein electrophoresis is endosmosis. All of the proteins have a net negative charge but gamma globulin can flow toward the cathode due to endosmosis. Endosmosis is the motion of liquid induced by an applied potential. The effects are fairly negligible but since the net negative charge of the gamma globulins can be small it can travel backward. Endosmosis is somewhat analogous to the wake created while lap swimming.
Nerdy Note:
Michael Faraday, (1791-1867), a famous English scientist known for his work on electricity and magnetism popularized the words cation, anion, cathode, and anode.
Study Tip:
To some it may seem counterintuitive that cations are positively charged but cathodes are negatively charged. These terms were created to be intuitive because cations flow to cathodes. Likewise, anions flow to anodes. If you’re ever in doubt Just remember “cats with ions are positive,” and you can logically figure out the rest.
There are four common SPEP patterns the clinical scientist should absolutely be aware of that result from the four following conditions: active cirrhosis, nephrotic syndrome, hypogammaglobulinemia, and monoclonal gammopathy.
Active cirrhosis:
In active cirrhosis, the pattern will have a decrease in albumin and an increase in the beta and gamma regions dubbed beta-gamma bridging. The decreased albumin is due to decreased synthesis. Albumin is synthesized in the liver. The increase in the beta-gamma region is due to decreased clearance of IgA antibodies which migrate in the beta and gamma regions. Increased IgA is related to the liver cirrhosis.
Nephrotic syndrome:
In nephrotic syndrome, the pattern will have a decrease in albumin and an increase in the alpha-2 region. The decreased albumin is due to increased permeability in the glomerular membrane of the kidney. The increased permeability causes an increase in protein lost in the urine. The increase in the alpha-2 region is due to the size of the protein α₂-macrogloblin (A2MG). Even with the increased permeability of the kidneys, it’s too big. In addition, the liver will increase protein synthesis of A2MG and A2MG can fill in for albumin in regards to oncotic pressure.
Hypogammaglobulinemia:
In hypogammaglobulinemia, the pattern will have a really low gamma globulin region. Anything that causes a decrease in the gamma globulins (IgG, IgA, IgM) like an immune deficiency can cause hypogammaglobulinemia.
Monoclonal gammopathy:
In a monoclonal gammopathy, the pattern will have a large spike in the gamma region. An immunoglobulin (IgG, IgM, IgA) from a single B-cell clone is produced in excess. These are mostly caused by hematological disorders including: multiple myeloma, lymphoma, CLL, Waldenstroms macroglobulinemia, heavy chain disease, and MGUS.
Immunofixation electrophoresis (IFE):
To further diagnose a monoclonal gammopathy an IFE can be performed. An IFE will separate the gamma region into IgG, IgA, IgM, kappa chains, and lambda chains. This test can help further differentiate what type of monoclonal gammopathy a patient has. IgG, IgA, and IgM are termed heavy chains and kappa and lambda, are termed light chains.
