Serum Immunoglobulins
February 15th, 2021
Overview
Immunoglobulins, secreted by plasma cells, are made up of five classes - IgG, IgM, IgA, IgD and IgE.
Roles of Immunoglobulins
- IgG - the most abundant immunoglobulin; also crosses the placenta
- IgM - the first immunoglobulin secreted in response to foreign antigens
- IgA - present in saliva, sweat, tears, breast milk and blood
- IgD - bound to B-cell membranes; triggers B-cell activation
- IgE - present in skin, mucous membranes and the lungs; involved in certain hypersensitivity reactions and response to parasitic infection
IgD and IgE are trace immunoglobulins and are not normally assessed.
Antibodies directed against specific pathogens (e.g. hepatitis B IgM and IgG) are useful in clinical practice, though total serum immunoglobulin levels are also useful for detecting inflammation, oligoclonal / monoclonal gammopathies and hypogammaglobulinaemia.
Elevated Immunoglobulins
Causes of Elevated Immunoglobulins
- Infection
- Inflammatory disease
- Malignancy
Causes of Single Ig Elevation
Plasma Cell Neoplasms
- Multiple myeloma
- Smouldering myeloma
- Monoclonal gammopathy of uncertain significance (MGUS)
- Solitary plasmacytoma
- AL amyloidosis
Others
- Waldenstrom's macroglobulinaemia
- Chronic lymphocytic leukaemia (CLL)
- Non-Hodgkin lymphoma (NHL)
- Monoclonal (type II) cryoglobulinaemia
Hypogammaglobulinaemia
Causes of Hypogammaglobulinaemia
Inherited
- Primary hypogammaglobulinaemia
Reduced Production
- Malnutrition
- Malignancy - especially CLL, lymphoma, multiple myeloma
- Inflammatory disease - SLE, rheumatoid arthritis
- Viruses - HIV, EBV, CMV, rubella
Increased Consumption
- Sepsis
- Severe burns
- Protein-losing enteropathy
- Nephrotic syndrome
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