Misplaced Pages

#428571

62-422: Antibodies are major components of humoral immunity . IgG is the main type of antibody found in blood and extracellular fluid , allowing it to control infection of body tissues . By binding many kinds of pathogens such as viruses , bacteria , and fungi , IgG protects the body from infection. It does this through several mechanisms: IgG antibodies are generated following class switching and maturation of

124-439: A B cell encounters an antigen, a signal is activated, the antigen binds to the receptor and is taken inside the B cell by endocytosis . The antigen is processed and presented on the B cell's surface again by MHC-II proteins . The MHC-II proteins are recognized by helper T cells , stimulating the production of proteins, allowing for B cells to multiply and the descendants to differentiate into antibody-secreting cells circulating in

186-451: A diagnostic tool for certain conditions, such as autoimmune hepatitis , if indicated by certain symptoms. Clinically, measured IgG antibody levels are generally considered to be indicative of an individual's immune status to particular pathogens. A common example of this practice are titers drawn to demonstrate serologic immunity to measles, mumps, and rubella (MMR), hepatitis B virus , and varicella (chickenpox), among others. Testing of IgG

248-599: A highly conserved N-glycosylation site at asparagine 297 in the constant region of the heavy chain. The N-glycans attached to this site are predominantly core-fucosylated biantennary structures of the complex type. In addition, small amounts of these N-glycans also bear bisecting GlcNAc and α-2,6-linked sialic acid residues. The N-glycan composition in IgG has been linked to several autoimmune, infectious and metabolic diseases. There are four IgG subclasses (IgG1, 2, 3, and 4) in humans, named in order of their abundance in serum (IgG1 being

310-592: A major tool in the standardization of immunity and the identification of lingering infections . Antibodies or Immunoglobulins are glycoproteins found within blood and lymph . Structurally, antibodies are large Y-shaped globular proteins . In mammals, there are five types of antibodies: immunoglobulin A , immunoglobulin D , immunoglobulin E , immunoglobulin G , and immunoglobulin M . Each immunoglobulin class differs in its biological properties and has evolved to deal with different antigens. Antibodies are synthesized and secreted by plasma cells that are derived from

372-647: A mechanism known as antibody-dependent enhancement of infection. There are several different types of Fc receptors (abbreviated FcR), which are classified based on the type of antibody that they recognize. The Latin letter used to identify a type of antibody is converted into the corresponding Greek letter, which is placed after the 'Fc' part of the name. For example, those that bind the most common class of antibody, IgG , are called Fc-gamma receptors (FcγR), those that bind IgA are called Fc-alpha receptors (FcαR) and those that bind IgE are called Fc-epsilon receptors (FcεR). The classes of FcRs are also distinguished by

434-536: A mixture of compounds including histamine , proteoglycans , and serine proteases . Activated mast cells also synthesize and secrete lipid -derived mediators (such as prostaglandins , leukotrienes , and platelet-activating factor ) and cytokines (such as interleukin 1 , interleukin 3 , interleukin 4 , interleukin 5 , interleukin 6 , interleukin 13 , tumor necrosis factor-alpha , GM-CSF , and several chemokines . These mediators contribute to inflammation by attracting other leukocytes . Large parasites like

496-678: A role in the homeostasis of IgG serum levels. Only one Fc receptor belongs to the FcαR subgroup, which is called FcαRI (or CD89). FcαRI is found on the surface of neutrophils , eosinophils, monocytes, some macrophages (including Kupffer cells ), and some dendritic cells . It is composed of two extracellular Ig-like domains, and is a member of both the immunoglobulin superfamily and the multi-chain immune recognition receptor (MIRR) family. It signals by associating with two FcRγ signaling chains. Another receptor can also bind IgA, although it has higher affinity for another antibody called IgM . This receptor

558-701: A sole IgG molecule (or monomer ), but all Fcγ receptors must bind multiple IgG molecules within an immune complex to be activated. The Fc-gamma receptors differ in their affinity for IgG and likewise the different IgG subclasses have unique affinities for each of the Fc gamma receptors. These interactions are further tuned by the glycan (oligosaccharide) at position CH2-84.4 of IgG. For example, by creating steric hindrance, fucose containing CH2-84.4 glycans reduce IgG affinity for FcγRIIIA. In contrast, G0 glycans, which lack galactose and terminate instead with GlcNAc moieties, have increased affinity for FcγRIIIA. Another FcR

620-423: A total molecular weight of about 150  kDa . The two heavy chains are linked to each other and to a light chain each by disulfide bonds . The resulting tetramer has two identical halves, which together form a Y-like shape. Each end of the fork contains an identical antigen binding site. The various regions and domains of a typical IgG are depicted in the figure "Anatomy of an IgG". The Fc regions of IgGs bear

682-519: Is a new costimulatory signal for human CD4+ T cells, which successfully substitute the CD28 requirement during autoimmunity. In an autoimmune background CD4+ T cells bypass the requirement of CD28 cosignaling to become fully activated. Furthermore, the blockade of CD28 cosignaling does not inhibit the development of TFH cells, a key subset for the generation of autoantibody producing autoreactive plasma B cells. A balance among costimulatory and inhibitory signals

SECTION 10

#1733084908429

744-513: Is a specific sequence of amino acids (YXXL) occurring twice in close succession in the intracellular tail of a receptor. When phosphate groups are added to the tyrosine (Y) residue of the ITAM by membrane-anchored enzymes of the Src kinase family , a signaling cascade is generated within the cell. This phosphorylation reaction typically follows interaction of an Fc receptor with its ligand . An ITAM

806-429: Is called CD16 or FcγRIII. Activation of FcγRIII by IgG causes the release of cytokines such as IFN-γ that signal to other immune cells, and cytotoxic mediators like perforin and granzyme that enter the target cell and promote cell death by triggering apoptosis . This process is known as antibody-dependent cell-mediated cytotoxicity (ADCC). FcγRIII on NK cells can also associate with monomeric IgG (i.e., IgG that

868-494: Is called the Fc-alpha/mu receptor (Fcα/μR) and is a type I transmembrane protein . With one Ig-like domain in its extracellular portion, this Fc receptor is also a member of the immunoglobulin superfamily. Two types of FcεR are known: Fc receptors are found on a number of cells in the immune system including phagocytes like macrophages and monocytes , granulocytes like neutrophils and eosinophils , and lymphocytes of

930-431: Is expressed on multiple cell types and is similar in structure to MHC class I . This receptor also binds IgG and is involved in preservation of this antibody. However, since this Fc receptor is also involved in transferring IgG from a mother either via the placenta to her fetus or in milk to her suckling infant , it is called the neonatal Fc receptor ( FcRn ). Recently, research suggested that this receptor plays

992-478: Is initiated by bacterial carbohydrate motifs, such as mannose, found on the surface of bacterium. After the binding process, the same subunit cleavage and synthesis occurs as in the classical pathway. The alternate complement pathway completely diverges from the previous pathways, as this pathway spontaneously initiates in the presence of hydrolyzed C3, which then recruits other subunits which can be cleaved to form C3 convertase. In all three pathways, once C3 convertase

1054-564: Is mainly important for regulation of activated B cells. The positive B cell signaling is initiated by binding of foreign antigen to surface immunoglobulin. The same antigen-specific antibody is secreted and it can feedback-suppress, or promote negative signaling. This negative signaling is being provided by FcγRIIB.: Experiments using B cell deletion mutants and dominant-negative enzymes have firmly established an important role for SH2-domain-containing inositol 5-phosphatase (SHIP) in negative signaling. Negative signaling through SHIP appears to inhibit

1116-486: Is not antigen-bound). When this occurs, the Fc receptor inhibits the activity of the NK cell. IgE antibodies bind to antigens of allergens . These allergen-bound IgE molecules interact with Fcε receptors on the surface of mast cells . Activation of mast cells following engagement of FcεRI results in a process called degranulation , whereby the mast cell releases preformed molecules from its cytoplasmic granules; these are

1178-435: Is not indicated for diagnosis of allergy, and there is no evidence that it has any relationship to food intolerances. Humoral immunity Humoral immunity is the aspect of immunity that is mediated by macromolecules – including secreted antibodies , complement proteins , and certain antimicrobial peptides – located in extracellular fluids . Humoral immunity is named so because it involves substances found in

1240-503: Is not sufficient to activate cells, and represents a motif (I/VXXYXXL) known as an immunoreceptor tyrosine-based inhibitory motif (ITIM). FcγRIIB1 and FcγRIIB2 have an ITIM sequence and are inhibitory Fc receptors; they do not induce phagocytosis. Inhibitory actions of these receptors are controlled by enzymes that remove phosphate groups from tyrosine residues; the phosphatases SHP-1 and SHIP-1 inhibit signaling by Fcγ receptors. Binding of ligand to FcγRIIB leads to phosphorylation of

1302-474: Is present in the intracellular tail of FcγRIIA, and its phosphorylation induces phagocytosis in macrophages. FcγRI and FcγRIIIA do not have an ITAM but can transmit an activating signal to their phagocytes by interacting with another protein that does. This adaptor protein is called the Fcγ subunit and, like FcγRIIA, contains the two YXXL sequences that are characteristic of an ITAM. The presence of only one YXXL motif

SECTION 20

#1733084908429

1364-408: Is produced, which dampens down inflammation by helping to curtail FcR-mediated processes. The relative ability of different IgG subclasses to fix complement may explain why some anti-donor antibody responses do harm a graft after organ transplantation. In a mouse model of autoantibody mediated anemia using IgG isotype switch variants of an anti erythrocytes autoantibody, it was found that mouse IgG2a

1426-465: Is relatively different. Given the opposing properties of the IgG subclasses (fixing and failing to fix complement; binding and failing to bind FcR), and the fact that the immune response to most antigens includes a mix of all four subclasses, it has been difficult to understand how IgG subclasses can work together to provide protective immunity. In 2013, the Temporal Model of human IgE and IgG function

1488-582: Is synthesized, complements are cleaved into subunits which either form a structure called the membrane attack complex (MAC) on the bacterial cell wall to destroy the bacteria or act as cytokines and chemokines, amplifying the immune response. Fc receptor In immunology , an Fc receptor is a protein found on the surface of certain cells  – including, among others, B lymphocytes , follicular dendritic cells , natural killer cells , macrophages , neutrophils , eosinophils , basophils , human platelets , and mast cells  – that contribute to

1550-399: Is that hemoglobin released by the destruction of red blood cells can cause acute kidney failure . In humoral immune response, the naive B cells begin the maturation process in the bone marrow, gaining B-cell receptors (BCRs) along the cell surface. These BCRs are membrane-bound protein complexes that have a high binding affinity for specific antigens ; this specificity is derived from

1612-584: The FcεRII receptor with the Fc portion of helminth bound IgE causes the eosinophil to release these molecules in a mechanism similar to that of the NK cell during ADCC. CD4+ T cells ( mature T h cells ) provide help to B cells that produce antibodies. Several subsets of activated effector CD4+ T cells are observed in disease pathology. Earlier studies summarized by Sanders and Lynch in 1993 suggested critical roles for FcRs in CD4+ T cell mediated immune responses and proposed

1674-648: The Ras pathway through SH2 domain competition with Grb2 and Shc and may involve consumption of intracellular lipid mediators that act as allosteric enzyme activators or that promote entry of extracellular Ca2+. When IgG molecules, specific for a certain antigen or surface component, bind to the pathogen with their Fab region (fragment antigen binding region), their Fc regions point outwards, in direct reach of phagocytes . Phagocytes bind those Fc regions with their Fc receptors. Many low affinity interactions are formed between receptor and antibody that work together to tightly bind

1736-533: The complement pathway . An incompatible blood transfusion causes a transfusion reaction , which is mediated by the humoral immune response. This type of reaction, called an acute hemolytic reaction, results in the rapid destruction (hemolysis) of the donor red blood cells by host antibodies. The cause is usually a clerical error, such as the wrong unit of blood being given to the wrong patient. The symptoms are fever and chills, sometimes with back pain and pink or red urine ( hemoglobinuria ). The major complication

1798-521: The helminth (worm) Schistosoma mansoni are too large for ingestion by phagocytes. They also have an external structure called an integument that is resistant to attack by substances released by macrophages and mast cells. However, these parasites can become coated with IgE and recognized by FcεRII on the surface of eosinophils . Activated eosinophils release preformed mediators such as major basic protein , and enzymes such as peroxidase , against which helminths are not resistant. The interaction of

1860-571: The humors , or body fluids . It contrasts with cell-mediated immunity . Humoral immunity is also referred to as antibody-mediated immunity . The study of the molecular and cellular components that form the immune system , including their function and interaction, is the central science of immunology . The immune system is divided into a more primitive innate immune system and an acquired or adaptive immune system of vertebrates , each of which contain both humoral and cellular immune elements. Humoral immunity refers to antibody production and

1922-413: The innate immune system ( natural killer cells ) or adaptive immune system (e.g., B cells ). They allow these cells to bind to antibodies that are attached to the surface of microbes or microbe infected cells, helping these cells to identify and eliminate microbial pathogens . The Fc receptors bind the antibodies at their Fc region (or tail), an interaction that activates the cell that possesses

Immunoglobulin G - Misplaced Pages Continue

1984-806: The mast cell receptor FcεRI, stimulating the release of both histamine and platelet activating factor (PAF). In the alternative pathway antigens form complexes with IgG, which then cross-link macrophage receptor FcγRIII and stimulates only PAF release. IgG antibodies can prevent IgE mediated anaphylaxis by intercepting a specific antigen before it binds to mast cell–associated IgE. Consequently, IgG antibodies block systemic anaphylaxis induced by small quantities of antigen but can mediate systemic anaphylaxis induced by larger quantities. IgG antibodies are large globular proteins made of four peptide chains; two identical γ (gamma) heavy chains of about 50 kDa and two identical light chains of about 25 kDa. The resulting tetrameric quaternary structure, therefore, has

2046-461: The B cell. These daughter cells either become plasma cells or memory cells . The memory B cells remain inactive here; later, when these memory B cells encounter the same antigen due to reinfection, they divide and form plasma cells. On the other hand, the plasma cells produce a large number of antibodies which are released freely into the circulatory system . These antibodies will encounter antigens and bind with them. This will either interfere with

2108-472: The B cells of the immune system. An antibody is used by the acquired immune system to identify and neutralize foreign objects like bacteria and viruses. Each antibody recognizes a specific antigen unique to its target. By binding their specific antigens, antibodies can cause agglutination and precipitation of antibody-antigen products, prime for phagocytosis by macrophages and other cells, block viral receptors, and stimulate other immune responses, such as

2170-432: The Fc receptor. Activation of phagocytes is the most common function attributed to Fc receptors. For example, macrophages begin to ingest and kill an IgG -coated pathogen by phagocytosis following engagement of their Fcγ receptors. Another process involving Fc receptors is called antibody-dependent cell-mediated cytotoxicity (ADCC). During ADCC, FcγRIII receptors on the surface of natural killer (NK) cells stimulate

2232-411: The Fc receptors of the phagocyte results in the initiation of phagocytosis . The pathogen becomes engulfed by the phagocyte by an active process involving the binding and releasing of the Fc region/Fc receptor complex, until the cell membrane of the phagocyte completely encloses the pathogen. The Fc receptor on NK cells recognize IgG that is bound to the surface of a pathogen-infected target cell and

2294-469: The FcR ligand to activated CD4+ T cells. CD16a expression is induced in the activated human naïve CD4+ T cells, which express CD25, CD69, and CD98 and ligation to ICs leads to generation of effector memory cells. CD16a signaling is mediated by phosphorylation of Syk (pSyk). A study now suggests induced expression of CD32a upon activation of human CD4+ T cells, similar to CD16a. CD32a expression on CD4+ T cells

2356-403: The NK cells to release cytotoxic molecules from their granules to kill antibody-covered target cells. FcεRI has a different function. FcεRI is the Fc receptor on granulocytes , that is involved in allergic reactions and defense against parasitic infections . When an appropriate allergic antigen or parasite is present, the cross-linking of at least two IgE molecules and their Fc receptors on

2418-452: The activity of the toxin and could transfer immunity to non-immune animals. In 1897, Paul Ehrlich showed that antibodies form against the plant toxins ricin and abrin , and proposed that these antibodies are responsible for immunity. Ehrlich, with his colleague von Behring, went on to develop the diphtheria antitoxin , which became the first major success of modern immunotherapy . The discovery of specified compatible antibodies became

2480-471: The amino acid sequence of the heavy and light polypeptide chains that constitute the variable region of the BCR. Once a BCR interacts with an antigen, it creates a binding signal which directs the B cell to produce a unique antibody that only binds with that antigen . The mature B cells then migrate from the bone marrow to the lymph nodes or other lymphatic organs , where they begin to encounter pathogens. When

2542-408: The analysis of antibacterial activity of the serum components. Hans Buchner is credited with the development of the humoral theory. In 1890, Buchner described alexins as "protective substances" that exist in the blood serum and other bodily fluids and are capable of killing microorganisms . Alexins, later redefined as "complements" by Paul Ehrlich , were shown to be the soluble components of

Immunoglobulin G - Misplaced Pages Continue

2604-438: The antibody response, thus they participate predominantly in the secondary immune response . IgG is secreted as a monomer that is small in size allowing it to easily diffuse into tissues. It is the only antibody isotype that has receptors to facilitate passage through the human placenta , thereby providing protection to the fetus in utero . Along with IgA secreted in the breast milk , residual IgG absorbed through

2666-405: The antibody-coated microbe. The low individual affinity prevents Fc receptors from binding antibodies in the absence of antigen, and therefore reduces the chance of immune cell activation in the absence of infection. This also prevents agglutination (clotting) of phagocytes by antibody when there is no antigen. After a pathogen has been bound, interactions between the Fc region of the antibody and

2728-422: The blood. B cells can be activated through certain microbial agents without the help of T-cells and have the ability to work directly with antigens to provide responses to pathogens present. The B cell waits for a helper T cell (T H ) to bind to the complex. This binding will activate the T H cell, which then releases cytokines that induce B cells to divide rapidly, making thousands of identical clones of

2790-787: The cells that express them (macrophages, granulocytes, natural killer cells, T and B cells) and the signalling properties of each receptor. All of the Fcγ receptors (FcγR) belong to the immunoglobulin superfamily and are the most important Fc receptors for inducing phagocytosis of opsonized (marked) microbes. This family includes several members, FcγRI (CD64), FcγRIIA ( CD32 ), FcγRIIB (CD32), FcγRIIIA (CD16a), FcγRIIIB (CD16b), which differ in their antibody affinities due to their different molecular structure . For instance, FcγRI binds to IgG more strongly than FcγRII or FcγRIII does. FcγRI also has an extracellular portion composed of three immunoglobulin (Ig)-like domains , one more domain than FcγRII or FcγRIII has. This property allows FcγRI to bind

2852-451: The chemical interaction between host and foreign cells, or they may form bridges between their antigenic sites hindering their proper functioning. Their presence might also attract macrophages or killer cells to attack and phagocytose them. The complement system is a biochemical cascade of the innate immune system that helps clear pathogens from an organism. It is derived from many small blood plasma proteins that work together to disrupt

2914-475: The coinciding processes that accompany it, including: Th2 activation and cytokine production, germinal center formation and isotype switching, and affinity maturation and memory cell generation. It also refers to the effector functions of antibodies, which include pathogen and toxin neutralization, classical complement activation, and opsonin promotion of phagocytosis and pathogen elimination. The concept of humoral immunity developed based on

2976-446: The formation of a joint signaling complex among FcRs and TCR on the cell surface. Chauhan and coworkers reported the colocalization of the labeled ICs with the CD3 complex on activated CD4+ T cell surface, which thus suggest the coexistence of FcRs together with TCR complex. Both of these receptors are observed forming an apical structure on the membrane of activated CD4+ T cells, suggesting

3038-641: The innate response that leads to a combination of cellular and humoral immunity. This discovery helped to bridge the features of innate and acquired immunity . Following the 1888 discovery of the bacteria that cause diphtheria and tetanus , Emil von Behring and Kitasato Shibasaburō showed that disease need not be caused by microorganisms themselves. They discovered that cell-free filtrates were sufficient to cause disease. In 1890, filtrates of diphtheria, later named diphtheria toxins , were used to vaccinate animals in an attempt to demonstrate that immunized serum contained an antitoxin that could neutralize

3100-494: The lateral movement of these receptors. Co-migration of FcRs with TCR and BCR complex is observed on the cells surface and T:B cell cytoconjugates show this coexistence at the point of contact. An earlier review suggested that the expression of FcRs on CD4+ T cells is an open question. This established the current paradigm that T cells do not express FcRs and these findings were never challenged and experimentally tested. Chauhan and coworkers showed binding of immune complexes (ICs),

3162-411: The marking of pathogens for phagocytosis. The proteins account for 5% of the serum globulin fraction. Most of these proteins circulate as zymogens , which are inactive until proteolytic cleavage . Three biochemical pathways activate the complement system: the classical complement pathway , the alternate complement pathway , and the mannose-binding lectin pathway . These processes differ only in

SECTION 50

#1733084908429

3224-407: The most abundant). Note: IgG affinity to Fc receptors on phagocytic cells is specific to individual species from which the antibody comes as well as the class. The structure of the hinge regions (region 6 in the diagram) contributes to the unique biological properties of each of the four IgG classes. Even though there is about 95% similarity between their Fc regions, the structure of the hinge regions

3286-526: The pathogens that the mother encountered in her life (even if only through vaccination) until these antibodies are degraded. This repertoire of immunoglobulins is crucial for the newborns who are very sensitive to infections, especially within the respiratory and digestive systems. IgG are also involved in the regulation of allergic reactions. According to Finkelman, there are two pathways of systemic anaphylaxis : antigens can cause systemic anaphylaxis in mice through classic pathway by cross-linking IgE bound to

3348-424: The placenta provides the neonate with humoral immunity before its own immune system develops. Colostrum contains a high percentage of IgG, especially bovine colostrum. In individuals with prior immunity to a pathogen, IgG appears about 24–48 hours after antigenic stimulation. Therefore, in the first six months of life, the newborn has the same antibodies as the mother and the child can defend itself against all

3410-460: The process of activating C3 convertase , which is the initial step of complement activation, and the subsequent process are eventually the same. The classical pathway is initiated through exposure to free-floating antigen-bound antibodies. This leads to enzymatic cleavage of smaller complement subunits which synthesize to form the C3 convertase. This differs from the mannose-binding lectin pathway, which

3472-589: The protective functions of the immune system . Its name is derived from its binding specificity for a part of an antibody known as the Fc (fragment crystallizable) region . Fc receptors bind to antibodies that are attached to infected cells or invading pathogens . Their activity stimulates phagocytic or cytotoxic cells to destroy microbes , or infected cells by antibody-mediated phagocytosis or antibody-dependent cell-mediated cytotoxicity . Some viruses such as flaviviruses use Fc receptors to help them infect cells, by

3534-459: The surface of a granulocyte will trigger the cell to rapidly release preformed mediators from its granules. Fc gamma receptors belong to the group of non-catalytic tyrosine-phosphorylated receptors which share a similar signalling pathway involving phosphorylation of tyrosine residues. The receptors generate signals within their cells through an important activation motif known as an immunoreceptor tyrosine-based activation motif (ITAM). An ITAM

3596-440: The target cell's plasma membrane leading to cytolysis of the cell. The complement system consists of more than 35 soluble and cell-bound proteins, 12 of which are directly involved in the complement pathways. The complement system is involved in the activities of both innate immunity and acquired immunity. Activation of this system leads to cytolysis, chemotaxis , opsonization , immune clearance, and inflammation , as well as

3658-455: The tyrosine of the ITAM motif. This modification generates the binding site for the phosphatase, a SH2 recognition domain. The abrogation of ITAM activation signaling is caused by inhibition of protein tyrosine kinases of Src family, and by hydrolyzing the membrane PIP3 interrupting the further downstream signaling by the activating receptors, such as activating FcγRs, TCR, BCR and cytokine receptors (e.g. c-Kit). The negative signaling by FcγRIIB

3720-499: Was also suggested by three independent studies from HIV-1 researchers. The expression of CD16a and CD32a in a subset of activated CD4+ T cells is now confirmed. FcRs on the cell surface upon binding to ICs composed of nucleic acids trigger cytokine production and upregulate nucleic acid sensing pathways. FcRs are present both on the cell surface and in the cytosol. CD16a signaling upregulate the expression of nucleic acid sensing toll-like receptors and relocate them to cell surface. CD16a

3782-526: Was proposed. This model suggests that IgG3 (and IgE) appear early in a response. The IgG3, though of relatively low affinity, allows IgG-mediated defences to join IgM-mediated defences in clearing foreign antigens. Subsequently, higher affinity IgG1 and IgG2 are produced. The relative balance of these subclasses, in any immune complexes that form, helps determine the strength of the inflammatory processes that follow. Finally, if antigen persists, high affinity IgG4

SECTION 60

#1733084908429

3844-659: Was superior to IgG1 in activating complement. Moreover, it was found that the IgG2a isotype was able to interact very efficiently with FcgammaR. As a result, 20 times higher doses of IgG1, in relationship to IgG2a autoantibodies, were required to induce autoantibody mediated pathology. Since mouse IgG1 and human IgG1 are not entirely similar in function, and the inference of human antibody function from mouse studies must be done with great care. However, both human and mouse antibodies have different abilities to fix complement and to bind to Fc receptors . The measurement of immunoglobulin G can be

#428571