From the Guidelines
Antibodies in blood are a crucial component of the immune system, playing a key role in identifying and neutralizing foreign substances, with anti-nuclear antibodies (ANA) being a hallmark of autoimmunity, as noted in a 2014 study published in the Annals of the Rheumatic Diseases 1. Antibodies are specialized proteins produced by the immune system to defend against harmful invaders, such as bacteria and viruses.
- These Y-shaped molecules, also called immunoglobulins, are made by B cells when they detect foreign substances.
- There are five main types of antibodies: IgG, IgM, IgA, IgE, and IgD, each with distinct functions and roles in the immune response.
- Antibodies work by binding specifically to antigens on pathogens, marking them for destruction by other immune cells or directly neutralizing them. The detection of anti-cellular antibodies, such as ANA, is pivotal to the diagnosis of many autoimmune diseases, and specific antibodies may present years before the appearance of overt disease, as discussed in the study by Agmon-Levin et al. 1.
- The indirect immunofluorescence assay (IIFA) is considered the "gold standard" technique for ANA detection, but it has limitations, including a lack of specificity and the potential for false positives.
- Notably, some individuals with a positive ANA test by IIFA may not have an autoimmune disease and are unlikely to develop one, highlighting the importance of careful interpretation of test results, as noted in the 2014 study 1.
From the Research
Definition and Function of Antibodies
- Antibodies, also known as immunoglobulins, are protein molecules that contain antibody activity and are produced by the terminal cells of B-cell differentiation, known as 'plasma cells' 2.
- They provide essential protection from pathogens through their ability to recognize foreign antigens, aid in neutralization, and facilitate elimination from the host 3.
Classes of Immunoglobulins
- There are five classes of immunoglobulin (Ig): IgG, IgM, IgA, IgD, and IgE 2, 3.
- In normal serum, the distribution of these classes is approximately 80% IgG, 15% IgA, 5% IgM, 0.2% IgD, and a trace of IgE 2.
- Each class has distinct roles in mediating various aspects of the immune response, with IgA and IgM being the only ones capable of multimerization, allowing them to play critical roles in mucosal immunity 3.
Role of Immunoglobulins in Allergic Disease
- Immunoglobulin E (IgE)-mediated allergy is the most common hypersensitivity disease, and exposure to allergens can lead to the production of IgE antibodies in atopic individuals 4.
- Allergen-specific IgE, IgG, and IgA play complex roles in allergic diseases, with IgE being the primary mediator of allergic inflammation, while IgG and IgA can be induced to compete with IgE for binding with the allergen and prevent allergic responses 4.