Serum free light-chain measurement

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Serum free light-chain measurement
PurposeMeasurement of the serum level of FLCs

Free light chains (FLCs) are immunoglobulin light chains that are found in the serum (blood) in an unbound (free) state. In recent decades, measuring the amount of free light chains (FLCs) in the blood has become a practical clinical test. FLC tests can be used to diagnose and monitor diseases like multiple myeloma and amyloidosis.

Contents

Structure

Each immunoglobulin light-chain molecule contains approximately 220 amino acids in a single polypeptide chain that is folded to form constant and variable region domains. Each domain comprises two β-pleated sheets. The sheets are linked by a disulfide bridge and together form a roughly barrel-shaped structure known as a β-barrel. The variable (V) domain of light chains has a high degree of structural diversity, particularly the antigen-binding region. In addition, the first 23 amino acids of the 1st variable domain framework region have a number of variations known as subgroups. Four kappa (Vκ1–Vκ4) and six lambda subgroups (Vλ1–Vλ6) can be identified. [1] The subgroup structures of FLCs influence their ability to polymerize (combine) and form proteins like amyloid fibrils. For example, the Vλ6 subgroup of FLCs is associated with a type of amyloidosis called AL amyloidosis, while the Vκ1 and Vκ4 subgroups are associated with a different type of amyloidosis called light-chain deposition disease. [2]

Synthesis

Kappa light-chain molecules are constructed from approximately 40 functional Vκ gene segments (chromosome 2), five Jκ gene segments and a single Cκ gene. Lambda molecules (chromosome 22) are constructed from about 30 Vλ gene segments and four pairs of functional Jλ gene segments and a Cλ gene. [3]

Light chains are incorporated into immunoglobulin molecules during B-cell development and are expressed initially on the surface of pre B-cells. Production of light chains occurs throughout the rest of B-cell development and in plasma cells, where secretion is highest. [2]

Production

The production of free immunoglobulin light chains in normal individuals is approximately 500 mg/day from bone marrow and lymph node cells. [1] [4] The production of immunoglobulin light chains is about 40% greater than the production of immunoglobulin heavy chains. This may simply be to allow for the proper structure of the intact immunoglobulin molecules, but it is also possible that free light chains have an immunological function. [5] There are approximately twice as many kappa-producing plasma cells as lambda plasma cells. Kappa free-light chains are normally monomeric, while lambda free-light chains tend to be dimeric, joined by disulphide bonds. Polymeric forms of both types of free light chain can also occur. [6]

Metabolism

In normal individuals, free light chains are rapidly cleared from the blood and catabolised by the kidneys. Monomeric free light chains are cleared in 2–4 hours, and dimeric light chains in 3–6 hours. [7] Removal may be prolonged to 2–3 days in people with complete renal failure. [1] [4] [8] Human kidneys are composed of approximately half a million nephrons. Each nephron contains a glomerulus with basement membrane pores that allow filtration of immunoglobulin light chains and other small molecules from the blood into the proximal tubule of the nephron. [1]

Filtered molecules are either excreted in the urine or may be specifically re-absorbed. Protein molecules that pass through the glomerular pores are either absorbed unchanged (such as albumin), degraded in the proximal tubular cells and absorbed (such as free light chains), or excreted as fragments. [9] This re-absorption is mediated by a receptor complex (megalin/cubulin) and prevents the loss of large amounts of protein into the urine. It is very efficient and can process 10–30 g of low-molecular-weight proteins per day, so under normal conditions no light chains pass beyond the proximal tubules. [10] [11] [12]

If immunoglobulin light chains are produced in sufficient amounts to overwhelm the proximal tubules' absorption mechanisms (usually due to the presence of a plasma cell tumour) the light chains enter the distal tubules and can appear in the urine (Bence Jones protein). The passage of large amounts of immunoglobulin light chains through the kidneys may cause inflammation or blockage of the kidney tubules. [2]

The distal tubules of the kidneys secrete large amounts of uromucoid (Tamm–Horsfall protein). This is the dominant protein in normal urine and is thought to be important in preventing ascending urinary infections. It is a relatively small glycoprotein (80 kDa) that aggregates into polymers of 20–30 molecules. It contains a short amino-acid sequence that can specifically bind to some free light chains. [13] Together they can form an insoluble precipitate which blocks the distal part of the nephrons. This is termed "cast nephropathy" or "myeloma kidney" and is typically found in patients with multiple myeloma. [14] [15] This can block the flow of urine causing the death of the respective nephrons. Rising concentrations of light chains are filtered by the remaining nephrons leading to a cycle of accelerating renal damage with rising concentrations of free light chains in the blood. [16] At the same time, the amount of free light chains entering the urine will be decreased and will be zero if the patient stops producing urine (anuria). Conversely, urine concentrations of free light chains could increase if renal function improved in a multiple myeloma patient receiving treatment. This could account for the poor correlation frequently seen when urine and serum free light-chain concentrations are compared. [17] [18] [19] [20]

The 500 mg of FLCs produced per day by the normal lymphoid system, however, flows through the glomeruli and is completely processed by the proximal tubules. If the proximal tubules of the nephrons are damaged or stressed (such as in hard exercise), filtered FLCs may not be completely metabolised and small amounts may then appear in the urine. [9]

Clinical use

Serum free light-chain assays have been used in a number of published studies which have indicated superiority over the urine tests, particularly for patients producing low levels of monoclonal free light chains, as seen in nonsecretory multiple myeloma [21] [22] [23] and AL amyloidosis. [23] [24] [25] [26] This is primarily because of the re-absorption of free light chains in the kidneys, creating a threshold of light chain production which must be exceeded before measurable quantities overflow into the urine. [17] [18] [19] While there are a number of publications indicating that serum free light chain analysis is preferable to urine analysis at diagnosis, [27] [28] [29] [30] there is currently no consensus on whether urine tests for monitoring should be replaced. [18] [19] [20] [31]

A series of studies, principally from the Mayo Clinic, have indicated that patients with an abnormal free kappa to free lambda ratio have an increased risk of progression to active myeloma from precursor conditions including monoclonal gammopathy of undetermined significance (MGUS), [32] [33] smouldering myeloma [34] and solitary plasmacytoma of the bone. [35] Abnormal free light chain production has also been reported to be prognostic of a worse outcome in multiple myeloma [36] [37] [38] and chronic lymphocytic leukaemia. [39] An abnormal light-chain ratio has been defined as a kappa to lambda chain ratio of less than 0.26 or more than 1.65. [32]

Guidelines

In 2009, the International Myeloma Working Group published guidelines making recommendations of when serum free light-chain analysis should be used in the management of multiple myeloma. [40]

Diagnosis

The serum free light-chain assay in combination with serum protein electrophoresis and serum immunofixation electrophoresis is sufficient to screen for pathological monoclonal plasmaproliferative disorders other than AL amyloidosis which requires all the serum tests as well as 24 h urine immunofixation electrophoresis.

Monitoring

Serial serum free light-chain measurement should be routinely performed in patients with AL amyloidosis and multiple myeloma patients with oligosecretory disease. It should also be done in all patients who have achieved a complete response to treatment to determine whether they have attained a stringent complete response. [41]

Other guidelines for the use of serum free light chain measurement in the management of AL amyloidosis, [42] plasmacytoma [43] and the comparison of treatment responses in clinical trials [44] have also been published.

Technical and clinical reviews of serum free light-chain measurement have recently been written by Pratt and Jagannath. [45] [46]

Related Research Articles

<span class="mw-page-title-main">Proteinuria</span> Presence of an excess of serum proteins in the urine

Proteinuria is the presence of excess proteins in the urine. In healthy persons, urine contains very little protein, less than 150 mg/day; an excess is suggestive of illness. Excess protein in the urine often causes the urine to become foamy. Severe proteinuria can cause nephrotic syndrome in which there is worsening swelling of the body.

<span class="mw-page-title-main">Serum protein electrophoresis</span> Laboratory test

Serum protein electrophoresis is a laboratory test that examines specific proteins in the blood called globulins. The most common indications for a serum protein electrophoresis test are to diagnose or monitor multiple myeloma, a monoclonal gammopathy of uncertain significance (MGUS), or further investigate a discrepancy between a low albumin and a relatively high total protein. Unexplained bone pain, anemia, proteinuria, chronic kidney disease, and hypercalcemia are also signs of multiple myeloma, and indications for SPE. Blood must first be collected, usually into an airtight vial or syringe. Electrophoresis is a laboratory technique in which the blood serum is applied to either an acetate membrane soaked in a liquid buffer, or to a buffered agarose gel matrix, or into liquid in a capillary tube, and exposed to an electric current to separate the serum protein components into five major fractions by size and electrical charge: serum albumin, alpha-1 globulins, alpha-2 globulins, beta 1 and 2 globulins, and gamma globulins.

<span class="mw-page-title-main">Multiple myeloma</span> Cancer of plasma cells

Multiple myeloma (MM), also known as plasma cell myeloma and simply myeloma, is a cancer of plasma cells, a type of white blood cell that normally produces antibodies. Often, no symptoms are noticed initially. As it progresses, bone pain, anemia, kidney dysfunction, and infections may occur. Complications may include hypercalcemia and amyloidosis.

<span class="mw-page-title-main">Cryoglobulinemia</span> Medical condition

Cryoglobulinemia is a medical condition in which the blood contains large amounts of pathological cold sensitive antibodies called cryoglobulins – proteins that become insoluble at reduced temperatures. This should be contrasted with cold agglutinins, which cause agglutination of red blood cells.

<span class="mw-page-title-main">Monoclonal gammopathy of undetermined significance</span> Medical condition

Monoclonal gammopathy of undetermined significance (MGUS) is a plasma cell dyscrasia in which plasma cells or other types of antibody-producing cells secrete a myeloma protein, i.e. an abnormal antibody, into the blood; this abnormal protein is usually found during standard laboratory blood or urine tests. MGUS resembles multiple myeloma and similar diseases, but the levels of antibodies are lower, the number of plasma cells in the bone marrow is lower, and it rarely has symptoms or major problems. However, since MGUS can lead to multiple myeloma, which develops at the rate of about 1.5% a year, or other symptomatic conditions, yearly monitoring is recommended.

<span class="mw-page-title-main">Bence Jones protein</span> Urinary protein

Bence Jones protein is a monoclonal globulin protein or immunoglobulin light chain found in the urine, with a molecular weight of 22–24 kDa. Detection of Bence Jones protein may be suggestive of multiple myeloma, or Waldenström's macroglobulinemia.

<span class="mw-page-title-main">Plasmacytoma</span> Growth of a plasma cell tumour within soft tissue or the axial skeleton

Plasmacytoma is a plasma cell dyscrasia in which a plasma cell tumour grows within soft tissue or within the axial skeleton.

<span class="mw-page-title-main">Monoclonal gammopathy</span> Excess myeloma protein or monoclonal gamma globulin in the blood

Monoclonal gammopathy, also known as paraproteinemia, is the presence of excessive amounts of myeloma protein or monoclonal gamma globulin in the blood. It is usually due to an underlying immunoproliferative disorder or hematologic neoplasms, especially multiple myeloma. It is sometimes considered equivalent to plasma cell dyscrasia. The most common form of the disease is monoclonal gammopathy of undetermined significance.

<span class="mw-page-title-main">Cardiac amyloidosis</span> Medical condition

Cardiac amyloidosis is a subcategory of amyloidosis where there is depositing of the protein amyloid in the cardiac muscle and surrounding tissues. Amyloid, a misfolded and insoluble protein, can become a deposit in the heart's atria, valves, or ventricles. These deposits can cause thickening of different sections of the heart, leading to decreased cardiac function. The overall decrease in cardiac function leads to a plethora of symptoms. This multisystem disease was often misdiagnosed, with a corrected analysis only during autopsy. Advancements of technologies have increased earlier accuracy of diagnosis. Cardiac amyloidosis has multiple sub-types including light chain, familial, and senile. One of the most studied types is light chain cardiac amyloidosis. Prognosis depends on the extent of the deposits in the body and the type of amyloidosis. New treatment methods are actively being researched in regards to the treatment of heart failure and specific cardiac amyloidosis problems.

<span class="mw-page-title-main">Myeloma protein</span> Abnormal immunoglobulin fragment

A myeloma protein is an abnormal antibody (immunoglobulin) or a fragment thereof, such as an immunoglobulin light chain, that is produced in excess by an abnormal monoclonal proliferation of plasma cells, typically in multiple myeloma or Monoclonal gammopathy of undetermined significance. Other terms for such a protein are monoclonal protein, M protein, M component, M spike, spike protein, or paraprotein. This proliferation of the myeloma protein has several deleterious effects on the body, including impaired immune function, abnormally high blood viscosity, and kidney damage.

In hematology, plasma cell dyscrasias are a spectrum of progressively more severe monoclonal gammopathies in which a clone or multiple clones of pre-malignant or malignant plasma cells over-produce and secrete into the blood stream a myeloma protein, i.e. an abnormal monoclonal antibody or portion thereof. The exception to this rule is the disorder termed non-secretory multiple myeloma; this disorder is a form of plasma cell dyscrasia in which no myeloma protein is detected in serum or urine of individuals who have clear evidence of an increase in clonal bone marrow plasma cells and/or evidence of clonal plasma cell-mediated tissue injury. Here, a clone of plasma cells refers to group of plasma cells that are abnormal in that they have an identical genetic identity and therefore are descendants of a single genetically distinct ancestor cell.

Amyloid light-chain (AL) amyloidosis, also known as primary amyloidosis, is the most common form of systemic amyloidosis. The disease is caused when a person's antibody-producing cells do not function properly and produce abnormal protein fibers made of components of antibodies called light chains. These light chains come together to form amyloid deposits which can cause serious damage to different organs. An abnormal light chain in urine is known as Bence Jones protein.

AA amyloidosis is a form of amyloidosis, a disease characterized by the abnormal deposition of fibers of insoluble protein in the extracellular space of various tissues and organs. In AA amyloidosis, the deposited protein is serum amyloid A protein (SAA), an acute-phase protein which is normally soluble and whose plasma concentration is highest during inflammation.

<span class="mw-page-title-main">Light chain deposition disease</span> Medical condition

Light chain deposition disease (LCDD) is a rare blood cell disease which is characterized by deposition of fragments of infection-fighting immunoglobulins, called light chains (LCs), in the body. LCs are normally cleared by the kidneys, but in LCDD, these light chain deposits damage organs and cause disease. The kidneys are almost always affected and this often leads to kidney failure. About half of people with light chain deposition disease also have a plasma cell dyscrasia, a spectrum of diseases that includes multiple myeloma, Waldenström's macroglobulinemia, and the monoclonal gammopathy of undetermined significance premalignant stages of these two diseases. Unlike in AL amyloidosis, in which light chains are laid down in characteristic amyloid deposits, in LCDD, light chains are deposited in non-amyloid granules.

Onconephrology is a specialty in nephrology that deals with the study of kidney diseases in cancer patients. A nephrologist who takes care of patients with cancer and kidney disease is called an onconephrologist. This branch of nephrology encompasses nephrotoxicity associated with existing and novel chemotherapeutics, kidney disease as it pertains to stem cell transplant, paraneoplastic kidney disorders, paraproteinemias, electrolyte disorders associated with cancer, and more as discussed below.

Smouldering myeloma is a disease classified as intermediate in a spectrum of step-wise progressive diseases termed plasma cell dyscrasias. In this spectrum of diseases, a clone of plasma cells secreting monoclonal paraprotein causes the relatively benign disease of monoclonal gammopathy of undetermined significance. This clone proliferates and may slowly evolve into more aggressive sub-clones that cause smouldering multiple myeloma. Further and more rapid evolution causes the overtly malignant stage of multiple myeloma and can subsequently lead to the extremely malignant stage of secondary plasma cell leukemia. Thus, some patients with smouldering myeloma progress to multiple myeloma and plasma cell leukemia. Smouldering myeloma, however, is not a malignant disease. It is characterised as a pre-malignant disease that lacks symptoms but is associated with bone marrow biopsy showing the presence of an abnormal number of clonal myeloma cells, blood and/or urine containing a myeloma protein, and a significant risk of developing into a malignant disease.

<span class="mw-page-title-main">Serum B-cell maturation antigen</span> Cleaved form of B-cell maturation antigen

Serum B-cell maturation antigen (sBCMA) is the cleaved form of B-cell maturation antigen (BCMA), found at low levels in the serum of normal patients and generally elevated in patients with multiple myeloma (MM). Changes in sBCMA levels have been found to correlate with a MM patient’s clinical status in response to treatment.

Monoclonal immunoglobulin deposition disease, or MIDD, is a disease characterised by the deposition of monoclonal immunoglobulins on the basement membrane of the kidney. Monoclonal immunoglobulins are produced by monoclonal plasma cells, which are found in a variety of plasma cell dyscrasias. The deposition of monoclonal immunoglobulins on the basement membrane of the kidney causes renal impairment. As well as the kidney, MIDD may also affect the liver, heart, peripheral nerves, lung and skin.

Crystal-storing histiocytosis is a form of histiocytosis which mostly occurs in people with monoclonal gammopathies. Histiocytosis is an excessive number of histiocytes. In the vast majority of crystal-storing histiocytosis cases, immunoglobulins accumulate within the cytoplasm of histiocytes; in rare cases clofazimine, cystine, silica, or Charcot–Leyden crystals may be found in the histiocytes instead. Non-immunoglobulin crystal-storing histiocytosis is mostly associated with non-malignant disorders, such as chronic inflammation or autoimmune abnormality conditions such as rheumatoid arthritis, Crohn's disease, or Helicobacter pylori gastritis. It may be a localised or generalised disease. Examples of locations where histiocytosis may occur include the lungs, pleura, stomach, kidney, bone marrow, thyroid, thymus, and parotid gland. The disease is described as generalised if two or more unrelated sites are involved.

Monoclonal gammopathy of renal significance (MGRS) are a group of kidney disorders that present with kidney damage due to nephrotoxic monoclonal immunoglobulins secreted by clonal plasma cells or B cells. By definition, people with MGRS do not meet criteria for multiple myeloma or other hematologic malignancies. The term MGRS was introduced in 2012 by the International Kidney and Monoclonal Gammopathy Research Group (IKMG). MGRS is associated with monoclonal gammopathy of undetermined significance (MGUS). People with MGUS have a monoclonal gammopathy but does not meet the criteria for the clonal burden nor the presence of end organ damage seen in hematologic malignancies. In a population based study based on the NHANES III health survey; 6% of patients with MGUS were subsequently classified as having MGRS. The prevalence and incidence of MGRS in the general population or in specific populations is not known but it is more prevalent in those over the age of 50 as there is a monoclonal protein (M-protein) present in 3% of those 50 and years older and 5% of those 70 years and older, placing those 50 and older at increased risk of MGRS.

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  36. ↑ Kyrtsonis MC, Vassilakopoulos TP, Kafasi N, et al. (May 2007). "Prognostic value of serum free light chain ratio at diagnosis in multiple myeloma". British Journal of Haematology. 137 (3): 240–43. doi:10.1111/j.1365-2141.2007.06561.x. PMID   17408464. S2CID   36047195.
  37. ↑ Snozek CL, Katzmann JA, Kyle RA, et al. (October 2008). "Prognostic value of the serum free light chain ratio in newly diagnosed myeloma: Proposed incorporation into the international staging system". Leukemia. 22 (10): 1933–7. doi:10.1038/leu.2008.171. PMC   2614406 . PMID   18596742.
  38. ↑ van Rhee F, Bolejack V, Hollmig K, et al. (August 2007). "High serum-free light chain levels and their rapid reduction in response to therapy define an aggressive multiple myeloma subtype with poor prognosis". Blood. 110 (3): 827–32. doi:10.1182/blood-2007-01-067728. PMC   1924775 . PMID   17416735.
  39. ↑ Pratt G, Harding S, Holder R, et al. (January 2009). "Abnormal serum free light chain ratios are associated with poor survival and may reflect biological subgroups in patients with chronic lymphocytic leukaemia". British Journal of Haematology. 144 (2): 217–22. doi:10.1111/j.1365-2141.2008.07456.x. PMID   19016722. S2CID   28394748.
  40. ↑ Dispenzieri A, Kyle R, Merlini G, et al. (February 2009). "International Myeloma Working Group guidelines for serum-free light-chain analysis in multiple myeloma and related disorders". Leukemia. 23 (2): 215–24. doi: 10.1038/leu.2008.307 . hdl: 2318/70035 . PMID   19020545. S2CID   28720792.
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  42. ↑ Gertz MA, Comenzo R, Falk RH, et al. (August 2005). "Definition of organ involvement and treatment response in immunoglobulin light chain amyloidosis (AL): A consensus opinion from the 10th International Symposium on Amyloid and Amyloidosis, Tours, France, 18–22 April 2004". American Journal of Hematology. 79 (4): 319–28. doi:10.1002/ajh.20381. PMID   16044444. S2CID   21769919.
  43. ↑ Hughes M, Soutar R, Lucraft H, Owen R, Bird J. "Guidelines on the diagnosis and management of solitary plasmacytoma of bone, extramedullary plasmacytoma and multiple solitary plasmacytomas: 2009 update" (PDF). UKMF Guidelines Working Group. Archived from the original (PDF) on 13 April 2009. Retrieved 8 July 2009.
  44. ↑ Durie BG, Harousseau JL, Miguel JS, et al. (September 2006). "International uniform response criteria for multiple myeloma". Leukemia. 20 (9): 1467–73. doi:10.1038/sj.leu.2404284. PMID   16855634. S2CID   14838196.
  45. ↑ Pratt G (May 2008). "The evolving use of serum free light chain assays in haematology". British Journal of Haematology. 141 (4): 413–22. doi: 10.1111/j.1365-2141.2008.07079.x . PMID   18318757. S2CID   40081613.
  46. ↑ Jagannath S (September 2007). "Value of serum free light chain testing for the diagnosis and monitoring of monoclonal gammopathies in hematology". Clinical Lymphoma & Myeloma. 7 (8): 518–23. doi:10.3816/CLM.2007.n.036. PMID   18021469.
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