ig
Table of Contents
immunoglobulins
see also:
introduction
- a group of “antibody” proteins which form the “humoral” immune system and are produced by B lymphocytes - see adaptive immunity
IgA
- a type of immunoglobulin that protects against infections of the mucous membranes lining the mouth, airways, and digestive tract
- serum IgA levels may be raised due to:
- pulmonary and gastrointestinal inflammatory diseases
- some autoimmune conditions
- liver disease
- plasma cell disorders
IgE
- immunoglobulin generally associated with allergic reactions, and parasitic infections
- it appears a protein, neuritin, prevents the over-production of IgE and thus allergies, anaphylaxis, asthma and many auto-immune conditions could be the result of a deficiency of neuritin according to researchers at the Australian National University (ANU) in 2021
IgG
- composed of two identical heavy (CH) chains and two identical light (L) chains
- usually have 2 identical antigen binding sites (on the Fab arms)
- the amino acid sequences of the various IgG subclasses are 90 to 95 percent homologous
- CH regions are encoded by C gene segments clustered on chromosome 14
- four subclasses: IgG1, IgG2, IgG3, and IgG4
- functional differences among the subclasses result from structural variation in both the Fc regions and the hinge regions
- IgG1 and IgG3 fix C1q most effectively, IgG2 weakly, and IgG4 not at all
- the Fc region is important in binding to phagocyte membrane Fc receptors and in initiating phagocytosis following “opsonization” of the target antigen by it being bound to IgG
- 60-70% of serum IgG is IgG1, 20-30% is IgG2, 5-8% is IgG3 and 1-4% is IgG4
- half-lives are ~ 21 days although IgG3 half-life is only ~9 days
- serum IgG levels may be raised due to:
- chronic active infection or inflammation
- in association with plasma cell disorders
IgM
- acute phase antibody response to an antigen
- raised serum IgM levels may be due to:
- nonspecific marker of inflammation
- can be associated with liver disease
immunoglobulin production diseases or gammopathies
excess production
- benign monoclonal IgG paraproteinaemia
- hyper IgM syndrome
- family of 5 genetic disorders characterised by relatively high IgM levels
- causes increased risk of infections and usually have thrombocytopenia and neutropenia
- Wiskott-Aldrich syndrome
- rare X-linked recessive disease characterized by eczema, thrombocytopenia, immune deficiency, and bloody diarrhoea
- IgM levels are reduced, IgA and IgE are elevated, and IgG levels can be normal, reduced, or elevated
- hyper-IgE syndrome
- causes eosinophilia, high levels of IgE, retained primary teeth, recurrent “cold” staphylococcal infections, recurrent candidial infections, unusual eczema-like skin rashes, severe lung infections that result in pneumatoceles
- AD and AR forms; thought to be caused by abnormal neutrophil chemotaxis due to decreased production of interferon gamma by T lymphocytes
- raised IgG4 levels:
- IgG4-related systemic disease (IgG4-RSD)
- rare
- autoimmune pancreatitis
- sialadenitis and salivary gland enlargement
- tumor-like swelling of involved organs
- may also occur in:
- atopic dermatitis
- allergen immunotherapy
- Loeffler’s syndrome, leiomyosarcoma, periarteritis nodosa, and mycosis fungoides
deficiency or dysgammaglobulinemia
- X-linked agammaglobulinemia
- complete lack of circulating B cells; 1 in 100,000 male newborns; Dx usually after a history of recurrent infections, mostly in the respiratory tract, through childhood
- transient hypogammaglobulinemia of infancy
- IgA deficiency
- mild illness, mostly asymptomatic but increased risk of infections such as sinusitis, chest infections and UTI
- risk of anaphylaxis to blood transfusions or intravenous immunoglobulin due to the presence of IgA in these blood products
- higher risk of developing autoimmune diseases in middle age
- 1 in 300 people;
- IgG sub-class deficiencies
- isolated primary IgM deficiency
- may be asymptomatic, but is also associated with recurrent infections, asthma, atopy, allergic rhinitis, Bloom's syndrome, coeliac disease, systemic lupus erythematosus (SLE) and malignancy
- prevalence 0.03% of general population and 0.1% of hospitalised patients
- common variable immunodeficiency
- group of over 150 primary immunodeficiencies
- low levels of IgG, IgA and/or IgM
- malabsorption, atrophic gastritis, inflammatory bowel disease (IBD), aphthous stomatitis, polyarthritis, candida infection in lungs,
- immunodeficiency–centromeric instability–facial anomalies syndrome (ICF) syndrome
- very rare AR disorder; childhood infections; hypertelorism, low-set ears, epicanthal folds and macroglossia.
ig.txt · Last modified: 2023/11/28 12:10 by gary1