Recognize foreign antigens and triggers a biologic response to eliminate the antigen.

Circulating antibodies protect by binding to and neutralizing some protein toxins by blocking attachment of some viruses, bacterial cells, by opsonizing bacteria, and by activating complement.

Play crucial roles in the immune response by recognizing foreign antigens and triggering effector mechanisms and physiologic responses that attempt to eliminate the invading organism bearing that antigen.

9 known isotypes named after the heavy chain isotype: IgG1, IgG2,

IgG3, IgG4, IgM, IgA1, IgA2, IgD and IgE.

Made up of four polypeptide chains-2 heavy chains and 2 light chains.

The 2 heavy chains and 2 light chains are identical.

The light chains are either kappa encoded on chromosome 2 or lambda encoded on chromosome 22.

IgG isotypes represents approximately 85% of all antibodies in serum.

IgG4 accounts for less than 5% of the total IgG and healthy adults.

There are four types of IgG, IgG1 makes up 60-70% of the total IgG, followed by IgG2 (20-30%), IgG3 (5-8%), and IgG4 (1-4%). 

IgA predominates in secretions.

Immunoglobulins bind to receptors for their Fc regions, and mediate many functions, including antibody-dependent cell-mediated cytotoxicity, phagocytosis, and clearance of immune complexes.

IgM plays a major role in the primary immune response.

IgM, IgG1, IgG3, and, to a lesser degree, IgG2, fix and activate complement by the classical pathway.

Most types of phagocytes bear receptors for the Fc of IgG.

Two types of light chains kappa and lambda.

Kappa/lambda ratio of whole immunoglobulin molecules is 2:1.

Kappa/lambda ratio of free light chains is 1:1.5.

There are eight types of heavy chains.

Chains are joined by disulfide bridges which allow mobility.

Intrachain disulfide bridges are present as well.

Heavy chains are flexible at the hinge region.

Heavy chains are encoded on chromosome 14 by a cluster of immunoglobulin heavy chain C-region genes for the production of 5 classes and subclasses of immunoglobulins that are IgM, IgG, IgA, IgG1-4, IgA1-2 and IgE.

Heavy chains have a variable region (V), containing highly variable amino acids sequence.

Heavy chains have a diversity (D) segment in which amino acids are highly variable and a constant segment (C ) where the amino acid sequence is constant.

Heavy chains have a (J) joining segment with moderately variable amino acid sequences.

B lymphocytes respond to antigens by switching from its original production of IgA and and IgD to any of the heavy chain isotope.

The selection of light chain kappa or lambda is retained oral the life of the B-cell, all of its clone and terminally differentiated plasma cells.

B cells and immunoglobulin secreting plasma cells manufacture almost twice as many light chains in their cytoplasm as heavy chains, preventing aggregation toxic free heavy chains.

Both normal and malignant plasma cells secrete both whole immunoglobulin and free light chains (F LC).

Light chains have a V,J and C segments as well.

V segments form part of the antigen binding sites, the Fab portion of the molecule.

The portion of the immunoglobulin which mediates the reactions of the antibody is the Fc portion.

Immune system can produce 10 to the 9th different antibody species to interact with antigens.

IgG1 major component to respond to protein antigens (anti tetanus and anti diptheria antibodies).

IgG2 responds to polysaccharide antigens (anti pneumococcal antibodies).

Catabolism is concentration dependent, with higher concentrations being cleared faster.

IgG has a half-life of 21-28 days.

The human immune system is capable of producing up to 10 to the ninth different anti-bodies that can interact with a variety of antigens.

The nine isotypes of immunoglobulin are named after their heavy chains.

85% of all adult aantibodies in the serum are made up of IgG isotypes.

Receptors in immunoglobulin Fc regions bound by their targets can mediate anti-body dependent cell mediated cytotoxicity, phagocytosis and clearance of immune complexes.

IgM plays a significant role in the primary immune response.

Immunoglobulins IgM, IgG1, IgG3, and IgG2 can fix and activate complement.

IgG1 is a major component of response to protein antigens.

IgG2 and some IgG3 are produced in response to polysaccharide antigens.

IgG 3 active in responding to respiratory viruses.

IgA is produced locally and secreted by mucosal membranes.

IgM is produced by mucosal membranes to a much lesser extent than is IgA.

The mucosal immune system represents the largest component of the immune system, containing approximately 75% of all lymphocytes and producing the majority of immunoglobulin in healthy persons.

IgG is the only immunoglobulin that can cross the placenta, and this occurs during the third trimester of pregnancy and provides the newborn infant with humeral immunity.

IgG is protective of the newborn for about six months, at which time and endogenous production of the IgG occurs.

Immunoglobulin analysis on serum protein electrophoresis divides globulins into three major fractions: alpha, the fastest moving, beta and gamma the slowest moving proteins.

The gamma globulin fraction on serum protein electrophoresis is primarily composed of immunoglobulins, with IgG as the largest component.

IgG is distributed throughout the volume of extracellular fluid.

Immunoglobulins are made by plasma cells.

Intact immunoglobulins are not cleared by the kidneys, but immunoglobulin fragments are.

Immunogloblin fragments may be detected in the urine in certain diseases, such as multiple myeloma.

Acquired hypogammaglobulinemia may be due to drugs, renal loss of immunoglobulins, gastrointestinal loss of immunoglobulins, B-cell related malignancies, and severe burns.

Acquired decrease in immunoglobulins seen in poor nutrition and severe illness.

Renal loss of immunoglobulins is seen with the nephrotic syndrome, along with loss of albumin.

Loss of immunoglobulins via the gastrointestinal tract can occur with protein losing enteropathies and lymphangiectasia.

Increased catabolism of immunoglobulins can occur with B-cell malignancies, severe burns and dystrophic myotonia.

Hypogammaglobulinemia seen with thymoma, lymphoma, protein losing enteropathy, proteinuria, malnutrition, and the use of immunosuppressive drugs.

Impaired production may be related to congenital disorders of B-cell development with partial or complete absence of Ig subtypes.

Whole immunoglobulins and free light chains were secreted from myriads of clones of plasma cells in response to 100s of milligrams of different antigens and spontaneously.

Immunoglobulin secreting plasma cells are found in the medullary cords nodes, the red pulp of the spleen, the bone marrow, and the mucosa.

The plasma cells in the lymph nodes and spleen mostly secrete IgM, the bone marrow IgG, IgA, IgM D., and IgE, and the mucosa IgA.

Secretion of kappa and lambda free light chains by the total body plasma cell pool is about 1 g per day.

Free light chains all mostly cleared through the renal glomeruli, with a serum half-life of 2-4 hours.

Free light chains and not detectable in the urine of healthy individuals because they are metabolized in the proximal tubules of the nephron.

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