Changes in Serum Protein Levels

Electrophoresis and other tests of serum proteins
The basic screening examination is the electrophoresis of serum proteins. A drop of serum is put onto the electrophoretic agarose gel and spread across the "starting line". It is then subjected to the electric field in a buffer-filled box. Thus, the strip with electrophoretic gel can become part of an electric circuit. Electric field causes the proteins to move in the gel. Different proteins travel through the gel with different speed and thus cover various distances from the origin during the given amount of time (generally half an hour). The speed depends on the size of the molecules (the bigger the molecule the slower the movement - this is due to the bigger resistance of the gel to the movement) and electric charge (more charged molecules travel faster due to bigger electric force acting on them). Thus, a protein or a group of proteins makes bands (or peaks) with maximum at the given distance from the origin. After fixation and staining, the amount of protein in individual bands is determined by absorption photometry. Concentrations of individual serum protein can be also assessed, using various separation and analytic methods.

Electrophoresis divides serum proteins into following bands:


 * Albumin: Covers the greatest distance, because its molecules are relatively small and carry significant negative charge in alkalic pH (at which serum protein electrophoresis is undertaken).
 * &alpha;1-globulin: Within this fraction is &alpha;1-antitrypsin, high density lipoprotein (HDL), thyroxine binding protein (TBG) and many acute phase proteins.
 * &alpha;2-globulin: Within is &alpha;2-macroglobulin, &alpha;2-antiplasmin, ceruloplasmin (binds copper), very low density lipoproteins (VLDL), haptoglobin (binds free plasma hemoglobin) and many acute phase proteins.
 * &beta;-globulin: This fraction is very often further divided into &beta;;1-globulin and &beta;;2-globulin fraction. Contains proteins as fibrinogen, transferrin, low density lipoprotein (LDL), C3 and C4 complement components.
 * &gamma;-globulin: Within is for example factor VIII, C-reactive protein and most importantly all the immunoglobulins

Dysproteinemia
Disproteinemia is any disorder/abnormality of protein content of blood. The concentration of a protein in blood depends on the ration between the rate of its synthesis and breakdown or excretion. If one or more fractions of globulins becomes more prominent, the ratio albumin-globulin - so called A/G coefficient changes (norm 1.5 - 2).

General causes of dysproteinemias:


 * Congenital (mutation or loss of a gene) or acquired
 * Loss of certain protein fractions:
 * Kidneys - proteinuria, damage to glomeruli
 * Skin - serious burns, extensive infections
 * Intestine - exsudative enteropathy
 * Disorders of proteosynthesis:
 * Liver - loss of function in cirhosis, hepatitis - decreased synthesis of many serum proteins, e.g. albumin, factor II and I.
 * Insufficient dietary protein intake - kwashiorkor
 * Hemoconcentration by loss of water, e.g. to interstice
 * Changes of plasma cell numbers (synthesize immunoglobulins)

Dysproteinemias comprised of changes in more fractions or proteins

 * Hyperproteinemia: Increase in concentration of all serum proteins or (alternatively) increase in some proteins only which leads, however, to increase of protein concentration as a whole. If all the proteins are in increased concentration, then the increase is in fact relative - caused only by the loss of water which has concentrating effect on plasma. The resulting increase of oncotic pressure leads to movement of water from interstitical fluid to plasma. Hyperproteinemia (and paraproteinemia) can result in hyperviscosity syndrome (see lower).
 * Hypoproteinemia: Decrease of the total concentration of serum proteins, particularly albumin. It is caused either by losses of proteins (to urine, to burned areas)or defficient protein production in liver.  It results in decrease of oncotic pressure of plasma and edemas.
 * Acute inflamation: A typical change is so called acute phase reaction, which is seen mainly as an increase in fractions of &alpha;1-globulins and &alpha;2-globulins.
 * Chronic inflamation: A typical change is an increase of the &gamma;-globulin fraction caused by magnified synthesis of IgG (or IgM). This in fact constitutes a polyclonal hyperimmunoglobulinemia, where the whole immune system is stimulated. It can be found in chronic infectious diseases, alergies, autoimmune disorders, malignancies. An increased level of Ig often represents more then a half of plasma proteins. Remark: Monoclonal hyperimmunoglobulinemia is the same thing as paraproteinemia.

Changes in Albumin
Analbuminemia: Rare genetic disorder, causing generalized or localized edemas. The oncotic pressure is decreased. Although albumin generally represents about 60% of serum proteins, it can be completely absent without causing serious complications. The level of globulins is elevated by compensatory reaction, the total protein concentration is, however, still below normal.

Changes in &alpha;1-globulins
Lack of &alpha;1-antitrypsin: Its level is decreased to about 10% of the norm. Large amounts of the protein are found in hepatocytes, apparently due to the defect in excretion mechanism, which can later result in cirhosis. Increased levels of elastase, trypsin and other proteinases in blood. There is a damage to the pulmonary connective tissue, causing an obstructive disease (juvenile emphysema). The heredity is autosomal recessive. However, heterozygotes also have a slight decrease of serum levels.

Changes in &alpha;2-globulins
Decrease in haptoglobin: Primary decrease is a result of a rare genetic disorder. Secondary decrease is due to hemolysis, when all the haptoglobin is spend by binding hemoglobin and free haptoglobin is not detectable. Whatever the form is, there aren't any significant clinical consequences.

Lack of ceruloplasmin - Wilson's disease: Ceruloplasmin is the most important copper binding protein in plasma. Its absence causes fast loss of copper into tissues or its excretion by kidneys. Subsequently is augmented the enteral absorption of copper, which keeps the positive balance of intake over losses. The copper is deposited mainly in brain, liver, proximal tubules of kidneys and cornea. For more information, you can visit regular wikipedia.

Changes in &beta;-globulins
Lack of transferin: Defect of iron transport in plasma; insufficient suply of iron to the hematopoietic tissue. The result is an iron defficiency anemia and hemosiderosis. Heredity is autosomal dominant.

Changes in &gamma;-globulins
Agammaglobulinemia:
 * Hereditary form is X-linked. There is almost complete lack of &gamma;-globulins in serum, their levels being around 100 mg/100ml (norm is 1600 mg/100 ml). Plasma cells are absent from the bone marrow, spleen and lymph nodes, apparently due to a defect in stem cell maturation.  The onset takes place after weaning of the baby, when protection by mother's antibodies is lost. There is a low resistance to bacterial infections (pneumonias, sepsis). Treatment: i.m. injections of immunoglobulins.
 * Acquired form is rare, manifestation takes place in adult men and women. The immunoglobulin levels are below 500 mg/ml. Plasma cells are absent from lymph nodes. The spleen and liver are enlarged. Symptoms:  Frequent infections, susceptibility to autoimmune diseases.

Dysgammaglobulinemia: Some types of Ig are missing, others are in normal or increased concentration. Most commonly, IgG or IgA is missing and IgM is increased (as well as the number of plasma cells synthesizing IgM). Symptoms: Susceptibility to infections, thrombocytopenia, autoimmune hemolytic anemia.

Hyperimmunoglobulinemia: Increased level of &gamma;-globulins caused by their elevated synthesis. Each clone of plasma cells produces just one immunoglobulin. Presence of elevated levels of Ig can be divided into monoclonal hyperimmunoglobulinemia (=paraproteinemia) and polyclonal hyperimmunoglobuilnemia.

Paraproteinemia
Paraproteinemia is a finding of a high concentration of monoclonal immunoglobulin or immunoglobulin fragment, so called paraprotein or serum M component (M for monoclonal) produced in any one of a diverse group of immunoproliferative disorders involving the proliferation of a single clone of cells. Alternativelly the group of (generally malignant) disorders causing paraproteinemia.

Based on the type of the plasma cells, either whole immunoglobulins of IgG or IgM class are produced or just light or heavy chains are synthesised. The presence of paraproteins manifests itself in serum electrophoresis as a narrow and high peak in the band of &gamma;-globulins. If only light chains are synthesized, it is called Bence-Jones protein. Bence-Jones protein is filtered into urine, but the dipstick method for proteinuria is not sensitive to it. Electrophoresis of urine or denaturation of the protein by heating it up is necessary to pick them up. Bence-Jones protein can cause a damage to the renal tubuli. Protein casts may form in distal tubuli and cause a nephropathy, while crystals may accumulate in the cytoplasm of proximal tubular cells (typically in MGUS -see lower), causing Fanconi syndrome.

The concentration of paraprotein in blood reflects the size of the pathological clone of plasma cells. A substantial increase in concentration can cause a so called hyperviscosity syndrome (retinopathy and other sight disorders, thrombosis, neurological manifestations). If the M component is composed of cryoglobulins, a specific disorder of microcirculation, so called Raynauld syndrome appears (cryoglobulins precipitate in colder acral parts of the body). The synthesis of paraprotein is also accompanied by reduction of synthesis of normal (other) immunoglobulins and by their increased degradation. Consequently, there is low immunity against infections.

The presence of paraprotein is characteristic of following lymphoproliferative disease: Multiple myeloma (plasmocytoma), primary amyloidosis, Waldenström's macroglobulinemia, heavy chain disease and MGUS (Monoclonal gammopathy of undetermined significance).

Multiple myeloma (plasmocytoma): Progresive damage to skeleton caused by diffuse neoplastic proliferation of plasma cells. There is an increased production of IgG or IgA, Bence-Jones protein (light chains), IgM. Liver, spleen nor lymph nodes are not enlarged. Bone tissue is excessively resorbed by osteoclasts, leading to fast development of osteoporosis, destructive and osteolytic changes of axial skeleton and pathological fractures. Hypercalcemia, damage to renal tubular function (glycosuria, aminoaciduria..). Normocytic and normochromic anemia.

Waldenström's macroglobulinemia: Significant increase of IgM (no proteinuria) caused by neoplastic proliferation of plasma cells in bone marrow, spleen, liver and lymph nodes. Hepatomegaly, splenomegaly, lymphadenopathy. Bone metabolism is not affected. Possibly presence of cryoglobulins and Raynauld's syndrome, anemia, haemorrhagic diathesis.

Primary amyloidosis: Develops on the basis of multiple myeloma. Fibrils of amyloid are composed of parts of light chains or whole light chains or parts of heavy chains. Symptom are non-specific (tiredness, loss of weight, syncopes...).

Heavy chain disease: Pathological production of parts of immunoglobulin heavy chains that are present in plasma as well as in urine. There are three types of the disease (based on three types of heavy chains): &gamma;,&alpha;,&mu;. It can accompany lymphoma or other lymphoproliferative disease.

MGUS - monoclonal gammopathy of undetermined significance: Expansion of one clone of plasma cells (producing mostly IgG or IgA), which, however, does not display malignant behaviour for unknown reasons. Relatively common, treatable.