2010-Biology of immunoglobulin light chains

Josieh — Wed, 08 Sep 2010 10:54:00 GMT

2010-Sep-Guidelines for use of serum free light chain assays

AmyC — Thu, 02 Sep 2010 14:11:45 GMT

25.6. “Uniform Response Criteria for MM” incorporating FLCs (2009):

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	<font color=#6633CC>'''Table 25.3. Diagnostic criteria for MM requiring systemic therapy'''</font><br>		<font color=#6633CC>'''Table 25.3. Diagnostic criteria for MM requiring systemic therapy'''</font><br>
-	<div style="text-align: left"><font color=#6633CC><nowiki>*</nowiki> ''In patients with no detectable M-~~component~~, serum ~~FREELITE~~ chain ~~(FLC)~~ assays can substitute and satisfy this criterion. For patients with no serum or urine M-~~component~~, the baseline bone marrow must have ~~>30~~% plasma cells. These patients are referred to as "nonsecretory myeloma".''</font><br>	+	<div style="text-align: left"><font color=#6633CC><nowiki></nowiki> ''In patients with no detectable M-protein, serum Freelite chain assays can substitute and satisfy this criterion. For patients with no serum or urine M-protein, the baseline bone marrow must have ≥30% plasma cells. These patients are referred to as "nonsecretory myeloma".'' </font><br><nowiki>*</nowiki> Must be attributable to the underlying plasma cell disorder.</div><br>
-	<nowiki>**</nowiki> Must be attributable to the underlying plasma cell disorder</div><br>	+

	<table class="type-d" width="800">		<table class="type-d" width="800">

Wikilite - Recent changes [en-gb]

2010-03-08-Sensitivity of serum free light chain assays

2010-Biology of immunoglobulin light chains

2010-03-08-Sensitivity of serum free light chain assays

2010-Biology of immunoglobulin light chains

2010-Sep-Guidelines for use of serum free light chain assays

2010-Biology of immunoglobulin light chains

2010-Sep-Guidelines for use of serum free light chain assays

← Older revision		Revision as of 10:54, 8 September 2010
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	== 3.1 Structure ==		== 3.1 Structure ==
	[[File:Fig3.1.jpg\|300px\|thumb\|left\|<font color=#6633CC>'''Figure 3.1''' An antibody molecule showing the heavy and light chain structure, together with free κ and λ FLCs.</font>]]		[[File:Fig3.1.jpg\|300px\|thumb\|left\|<font color=#6633CC>'''Figure 3.1''' An antibody molecule showing the heavy and light chain structure, together with free κ and λ FLCs.</font>]]
-	[[File:New_Pic_3.2.jpg\|300px\|thumb\|right\|<font color=#6633CC>'''Figure 3.2''' Aκ FLC molecule showing the constant region (left), and the variable region (right) with its alpha helix (red). </font> (Courtesy of J Hobbs)]]	+	[[File:New_Pic_3.2.jpg\|300px\|thumb\|right\|<font color=#6633CC>'''Figure 3.2''' A κ FLC molecule showing the constant region (left), and the variable region (right) with its alpha helix (red). </font> (Courtesy of J Hobbs)]]

	Antibody molecules have a two-fold symmetry and are composed of two identical heavy and light chains, each containing variable and constant domains. The variable domains of each light chain/heavy chain pair combine to form an antigen-binding site, so that both chains contribute to the antigen-binding specificity of the antibody molecule. Light chains are of two types, κ and λ, and in any given antibody molecule only one type occurs. Approximately twice as many κ as λ molecules are produced in humans but in other mammals this ratio can vary. Each free light chain (FLC) molecule contains approximately 220 amino acids in a single polypeptide chain that is folded to form the constant and variable region domains ''(Figures 3.1 and 3.2)''.		Antibody molecules have a two-fold symmetry and are composed of two identical heavy and light chains, each containing variable and constant domains. The variable domains of each light chain/heavy chain pair combine to form an antigen-binding site, so that both chains contribute to the antigen-binding specificity of the antibody molecule. Light chains are of two types, κ and λ, and in any given antibody molecule only one type occurs. Approximately twice as many κ as λ molecules are produced in humans but in other mammals this ratio can vary. Each free light chain (FLC) molecule contains approximately 220 amino acids in a single polypeptide chain that is folded to form the constant and variable region domains ''(Figures 3.1 and 3.2)''.
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	\|Val(191)		\|Val(191)
	\|}		\|}
-	<font color=#6633CC> '''Table 3.1''' – Amino acid substitutions in k constant domains.</font>	+	<font color=#6633CC> '''Table 3.1''' Amino acid substitutions in κ constant domains.</font>

	In contrast, the variable (V) domain has huge structural diversity, particularly in association with the antigen binding amino acids. In addition, the first 23 amino acids of the 1st variable domain framework region have a limited number of variations known as subgroups. Using monoclonal antibodies, 4 kappa (Vκ1 - Vκ4) and 6 lambda subgroups (Vλ1 - Vλ6) can be identified <ref name=Solomon>Solomon A. Light chains of human immunoglobulins. Methods Enzymol 1985; 116: 101 – 21 [http://www.ncbi.nlm.nih.gov/pubmed/3937021 PMID:3937021]</ref>. The specific subgroup structures influence the potential of the FLCs to polymerise such that AL amyloidosis is associated with Vλ6 and light chain deposition disease (LCDD) with Vκ1 and Vκ4.		In contrast, the variable (V) domain has huge structural diversity, particularly in association with the antigen binding amino acids. In addition, the first 23 amino acids of the 1st variable domain framework region have a limited number of variations known as subgroups. Using monoclonal antibodies, 4 kappa (Vκ1 - Vκ4) and 6 lambda subgroups (Vλ1 - Vλ6) can be identified <ref name=Solomon>Solomon A. Light chains of human immunoglobulins. Methods Enzymol 1985; 116: 101 – 21 [http://www.ncbi.nlm.nih.gov/pubmed/3937021 PMID:3937021]</ref>. The specific subgroup structures influence the potential of the FLCs to polymerise such that AL amyloidosis is associated with Vλ6 and light chain deposition disease (LCDD) with Vκ1 and Vκ4.
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	Figure 3.6 shows a nephron, of which there are approximately half a million in each kidney. Each nephron contains a glomerulus with basement membrane fenestrations, which allow filtration of serum molecules into the proximal tubules. The pore sizes are variable with a restriction in filtration commencing at about 20-40kDa and being complete by 60kDa. Protein molecules that pass through the glomerular pores are then either absorbed unchanged (as with albumin) or degraded in the proximal tubular cells and absorbed or excreted as fragments <ref name=Russo>Russo LM, Bakris GL, Comper WD. Renal handling of albumin: a critical review of basic concepts and perspective. Am J Kidney Dis 2002; 39: 899 – 919 [http://www.ncbi.nlm.nih.gov/pubmed/11979334 PMID:11979334] </ref>. This megalin/cubulin absorption pathway is important and is designed to prevent loss of large amounts of proteins and peptides into urine. It is very efficient and can process between 10-30g of small molecular weight proteins per day, so under normal conditions, none passes beyond the proximal tubules <ref name=Abraham>Abraham GN, Waterhouse C. Evidence for defective immunoglobulin metabolism in severe renal insufficiency. Am J Med Sci 1974; 268: 227 – 33 [http://www.ncbi.nlm.nih.gov/pubmed/4217565 PMID:4217565] </ref><ref name=Wochner>Wochner RD, Strober W, Waldmann TA. The role of the kidney in the catabolism of Bence Jones proteins and immunoglobulin fragments. J Exp Med 1967; 126: 207 – 21 [http://www.ncbi.nlm.nih.gov/pubmed/4165739 PMID:4165739] </ref><ref name=Maack> Maack T, Johnson V, Kau ST, Figueiredo J, Sigulem D. Renal filtration, transport, and metabolism of low-molecular-weight proteins: a review. Kidney Int 1979; 16: 251 – 70 [http://www.ncbi.nlm.nih.gov/pubmed/393891 PMID:393891] </ref>.		Figure 3.6 shows a nephron, of which there are approximately half a million in each kidney. Each nephron contains a glomerulus with basement membrane fenestrations, which allow filtration of serum molecules into the proximal tubules. The pore sizes are variable with a restriction in filtration commencing at about 20-40kDa and being complete by 60kDa. Protein molecules that pass through the glomerular pores are then either absorbed unchanged (as with albumin) or degraded in the proximal tubular cells and absorbed or excreted as fragments <ref name=Russo>Russo LM, Bakris GL, Comper WD. Renal handling of albumin: a critical review of basic concepts and perspective. Am J Kidney Dis 2002; 39: 899 – 919 [http://www.ncbi.nlm.nih.gov/pubmed/11979334 PMID:11979334] </ref>. This megalin/cubulin absorption pathway is important and is designed to prevent loss of large amounts of proteins and peptides into urine. It is very efficient and can process between 10-30g of small molecular weight proteins per day, so under normal conditions, none passes beyond the proximal tubules <ref name=Abraham>Abraham GN, Waterhouse C. Evidence for defective immunoglobulin metabolism in severe renal insufficiency. Am J Med Sci 1974; 268: 227 – 33 [http://www.ncbi.nlm.nih.gov/pubmed/4217565 PMID:4217565] </ref><ref name=Wochner>Wochner RD, Strober W, Waldmann TA. The role of the kidney in the catabolism of Bence Jones proteins and immunoglobulin fragments. J Exp Med 1967; 126: 207 – 21 [http://www.ncbi.nlm.nih.gov/pubmed/4165739 PMID:4165739] </ref><ref name=Maack> Maack T, Johnson V, Kau ST, Figueiredo J, Sigulem D. Renal filtration, transport, and metabolism of low-molecular-weight proteins: a review. Kidney Int 1979; 16: 251 – 70 [http://www.ncbi.nlm.nih.gov/pubmed/393891 PMID:393891] </ref>.

-	The distal tubule secretes 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 (80kDa) that aggregates into polymers of 20-30 molecules. Interestingly, it contains a short peptide motif that specifically binds FLCs <ref name=Ying>Ying WZ, Sanders PW. Mapping the Binding Domain of Immunoglobulin Light Chains for Tamm-Horsfall protein. Am J Path 2001; 158: 1859-1866 [http://www.ncbi.nlm.nih.gov/pubmed/11337384 PMID: 11337384]</ref>. Together they form waxy casts that are characteristically found in acute renal failure associated with light chain multiple myeloma (LCMM) (Figures 3.7A, 3.7B and [[The_kidney_and_monoclonal_free_light_chains\|Chapter 13]]) <ref name=Sanders> Sanders PW, Booker BB, Bishop JB, Cheung HC. Mechanisms of intranephronal proteinaceous cast formation by low molecular weight proteins. J Clin Invest 1990; 85: 570 - 6 [http://www.ncbi.nlm.nih.gov/pubmed/2298921 PMID:2298921] </ref><ref name=Sanders2> Sanders PW, Booker BB. Pathobiology of cast nephropathy from human Bence Jones proteins. J Clin Invest 1992; 89: 630 – 9 [http://www.ncbi.nlm.nih.gov/pubmed/1737851 PMID:1737851] </ref>.	+	The distal tubule secretes 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 (80kDa) that aggregates into polymers of 20-30 molecules. Interestingly, it contains a short peptide motif that specifically binds FLCs <ref name=Ying>Ying WZ, Sanders PW. Mapping the Binding Domain of Immunoglobulin Light Chains for Tamm-Horsfall protein. Am J Path 2001; 158: 1859-1866 [http://www.ncbi.nlm.nih.gov/pubmed/11337384 PMID: 11337384]</ref>. Together they form waxy casts that are characteristically found in acute renal failure associated with light chain multiple myeloma (LCMM) ''(Figures 3.7A, 3.7B and [[The_kidney_and_monoclonal_free_light_chains\|Chapter 13]])'' <ref name=Sanders> Sanders PW, Booker BB, Bishop JB, Cheung HC. Mechanisms of intranephronal proteinaceous cast formation by low molecular weight proteins. J Clin Invest 1990; 85: 570 - 6 [http://www.ncbi.nlm.nih.gov/pubmed/2298921 PMID:2298921] </ref><ref name=Sanders2> Sanders PW, Booker BB. Pathobiology of cast nephropathy from human Bence Jones proteins. J Clin Invest 1992; 89: 630 – 9 [http://www.ncbi.nlm.nih.gov/pubmed/1737851 PMID:1737851] </ref>.

	In normal individuals, 1-10mg of FLCs is excreted per day into the urine. Its exact origin is unclear but it probably enters the urine via the mucosal surfaces of the distal part of the nephrons and the urethra, alongside secretory IgA. This secretion is part of the mucosal defence system that prevents infectious agents entering the body. The 500mg of FLCs produced each day by the normal lymphoid system therefore flow through the glomeruli and is completely processed by the proximal tubules <ref name=Russo> Russo LM, Bakris GL, Comper WD. Renal handling of albumin: a critical review of basic concepts and perspective. Am J Kidney Dis 2002; 39: 899 – 919 [http://www.ncbi.nlm.nih.gov/pubmed/11979334 PMID:11979334] </ref>.		In normal individuals, 1-10mg of FLCs is excreted per day into the urine. Its exact origin is unclear but it probably enters the urine via the mucosal surfaces of the distal part of the nephrons and the urethra, alongside secretory IgA. This secretion is part of the mucosal defence system that prevents infectious agents entering the body. The 500mg of FLCs produced each day by the normal lymphoid system therefore flow through the glomeruli and is completely processed by the proximal tubules <ref name=Russo> Russo LM, Bakris GL, Comper WD. Renal handling of albumin: a critical review of basic concepts and perspective. Am J Kidney Dis 2002; 39: 899 – 919 [http://www.ncbi.nlm.nih.gov/pubmed/11979334 PMID:11979334] </ref>.
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	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 enter the urine. Although important as markers of general renal function, particularly glomerular function, serum creatinine and cystatin C measurements cannot detect such minor degrees of nephron dysfunction.		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 enter the urine. Although important as markers of general renal function, particularly glomerular function, serum creatinine and cystatin C measurements cannot detect such minor degrees of nephron dysfunction.

-	As noted above, due to their smaller size κ FLC monomers are cleared 2-3 times faster than dimeric λ molecules <ref name=Arfors>Arfors KE, Rutili G, Svensjo E. Microvascular transport of macromolecules in normal and inflammatory conditions. Acta Physiol Scand Suppl 1979; 463: 93 – 103 [http://www.ncbi.nlm.nih.gov/pubmed/382749 PMID:382749] </ref>. Although κ production rates are twice that of λ, their faster removal ensures that the actual serum concentrations are approximately 50% lower ([[Normal_ranges_and_reference_intervals\|Chapter 5]] and [[Renal_diseases_and_free_light_chains\|20]]).	+	As noted above, due to their smaller size κ FLC monomers are cleared 2-3 times faster than dimeric λ molecules <ref name=Arfors>Arfors KE, Rutili G, Svensjo E. Microvascular transport of macromolecules in normal and inflammatory conditions. Acta Physiol Scand Suppl 1979; 463: 93 – 103 [http://www.ncbi.nlm.nih.gov/pubmed/382749 PMID:382749] </ref>. Although κ production rates are twice that of λ, their faster removal ensures that the actual serum concentrations are approximately 50% lower ''([[Normal_ranges_and_reference_intervals\|Chapter 5]] and [[Renal_diseases_and_free_light_chains\|20]])''.

	Because of the huge metabolic capacity of the proximal tubule, the amount of FLCs in urine, even when production is considerably increased, is more dependent upon renal function than synthesis by the tumour. As a consequence, serum and urine FLC concentrations may not be similar during the evolution of LCMM. This is shown in a hypothetical patient in Figure 3.10. The red line shows the steady increase in sFLCs as the tumour grows over the first 12 months. When synthesis of FLCs exceeds 10-30g/day (greater than 30 times normal) there is an overflow proteinuria and large amounts of FLCs enter the urine. It is normally at this point that patients with LCMM are identified.		Because of the huge metabolic capacity of the proximal tubule, the amount of FLCs in urine, even when production is considerably increased, is more dependent upon renal function than synthesis by the tumour. As a consequence, serum and urine FLC concentrations may not be similar during the evolution of LCMM. This is shown in a hypothetical patient in Figure 3.10. The red line shows the steady increase in sFLCs as the tumour grows over the first 12 months. When synthesis of FLCs exceeds 10-30g/day (greater than 30 times normal) there is an overflow proteinuria and large amounts of FLCs enter the urine. It is normally at this point that patients with LCMM are identified.

-	When FLCs overwhelm the proximal tubules’ absorption mechanisms, they enter the distal tubules and may cause inflammation or precipitate as casts. This can block the flow of urine causing affected nephrons to perish (Figures 3.7A and 3.7B and [[The_kidney_and_monoclonal_free_light_chains\|Chapter 13]] and [[Renal_diseases_and_free_light_chains\|20]]). Rising concentrations of sFLCs are filtered by the remaining nephrons leading to a vicious cycle of accelerating renal damage with further increases in sFLC concentrations.	+	When FLCs overwhelm the proximal tubules’ absorption mechanisms, they enter the distal tubules and may cause inflammation or precipitate as casts. This can block the flow of urine causing affected nephrons to perish ''(Figures 3.7A and 3.7B)'' and ''([[The_kidney_and_monoclonal_free_light_chains\|Chapter 13]] and [[Renal_diseases_and_free_light_chains\|20]])''. Rising concentrations of sFLCs are filtered by the remaining nephrons leading to a vicious cycle of accelerating renal damage with further increases in sFLC concentrations.

	This process lengthens the serum half-life of FLCs so that concentrations rise rapidly as urine excretion decreases with the onset of terminal renal failure, falling to zero as the patient becomes aneuric ''(Figure 3.8)''. Consequently, the amounts of FLCs in serum and urine diverge during disease progression. While increasing serum concentrations indicate worsening disease, falling urine concentrations may falsely suggest disease stabilisation or improvement. For example, Nowrousian et al. showed that urine FLC excretion decreased at high sFLC concentrations when there was significant renal impairment <ref name=Nowrousian>Nowrousian, M. R., D. Brandhorst, et al. (2005). "Serum free light chain analysis and urine immunofixation electrophoresis in patients with multiple myeloma." Clin Cancer Res 11(24 Pt 1): 8706-14.</ref>. In contrast, successful treatment of tumours may lead to a reduction of tubular casts, increased urine flow and more FLCs in urine.		This process lengthens the serum half-life of FLCs so that concentrations rise rapidly as urine excretion decreases with the onset of terminal renal failure, falling to zero as the patient becomes aneuric ''(Figure 3.8)''. Consequently, the amounts of FLCs in serum and urine diverge during disease progression. While increasing serum concentrations indicate worsening disease, falling urine concentrations may falsely suggest disease stabilisation or improvement. For example, Nowrousian et al. showed that urine FLC excretion decreased at high sFLC concentrations when there was significant renal impairment <ref name=Nowrousian>Nowrousian, M. R., D. Brandhorst, et al. (2005). "Serum free light chain analysis and urine immunofixation electrophoresis in patients with multiple myeloma." Clin Cancer Res 11(24 Pt 1): 8706-14.</ref>. In contrast, successful treatment of tumours may lead to a reduction of tubular casts, increased urine flow and more FLCs in urine.

-	Understanding the nephrotoxicity of FLCs and how it can influence FLC concentrations in serum and urine is important. The inevitable conclusion, from the physiological and pathological mechanisms described above, is that serum is ~~preferableto~~ urine for assessing FLC concentrations.	+	Understanding the nephrotoxicity of FLCs and how it can influence FLC concentrations in serum and urine is important. The inevitable conclusion, from the physiological and pathological mechanisms described above, is that serum is preferable to urine for assessing FLC concentrations.

	{\| class="qacol collapsible" width=100% align=center		{\| class="qacol collapsible" width=100% align=center
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	#Is Bence Jones proteinuria “overflow”, “glomerular” or “tubular” in origin?”		#Is Bence Jones proteinuria “overflow”, “glomerular” or “tubular” in origin?”
	#What are the normal serum half-lives of IgG and FLCs?		#What are the normal serum half-lives of IgG and FLCs?
-	#Serum albumin concentrations are reduced in patients with nephrotic syndrome with gross proteinuria. Are ~~serum FLC~~ concentrations also reduced in these circumstances?	+	#Serum albumin concentrations are reduced in patients with nephrotic syndrome with gross proteinuria. Are sFLC concentrations also reduced in these circumstances?
	#Which protein binds FLCs in the distal tubules?		#Which protein binds FLCs in the distal tubules?
-	#Do urine FLC concentrations always increase alongside rising ~~serum FLC~~ concentrations?	+	#Do urine FLC concentrations always increase alongside rising sFLC concentrations?