What is Antibodies: Definition and 11 Discussions

An antibody (Ab), also known as an immunoglobulin (Ig), is a large, Y-shaped protein used by the immune system to identify and neutralize foreign objects such as pathogenic bacteria and viruses. The antibody recognizes a unique molecule of the pathogen, called an antigen. Each tip of the "Y" of an antibody contains a paratope (analogous to a lock) that is specific for one particular epitope (analogous to a key) on an antigen, allowing these two structures to bind together with precision. Using this binding mechanism, an antibody can tag a microbe or an infected cell for attack by other parts of the immune system, or can neutralize it directly (for example, by blocking a part of a virus that is essential for its invasion).
To allow the immune system to recognize millions of different antigens, the antigen-binding sites at both tips of the antibody come in an equally wide variety.
In contrast, the remainder of the antibody is relatively constant. It only occurs in a few variants, which define the antibody's class or isotype: IgA, IgD, IgE, IgG, or IgM.
The constant region at the trunk of the antibody includes sites involved in interactions with other components of the immune system. The class hence determines the function triggered by an antibody after binding to an antigen, in addition to some structural features.
Antibodies from different classes also differ in where they are released in the body and at what stage of an immune response.
Together with B and T cells, antibodies comprise the most important part of the adaptive immune system.
They occur in two forms: one that is attached to a B cell, and the other, a soluble form, that is unattached and found in extracellular fluids such as blood plasma.
Initially, all antibodies are of the first form, attached to the surface of a B cell – these are then referred to as B-cell receptors (BCR).
After an antigen binds to a BCR, the B cell activates to proliferate and differentiate into either plasma cells, which secrete soluble antibodies with the same paratope, or memory B cells, which survive in the body to enable long-lasting immunity to the antigen.
Soluble antibodies are released into the blood and tissue fluids, as well as many secretions.
Because these fluids were traditionally known as humors, antibody-mediated immunity is sometimes known as, or considered a part of, humoral immunity.
The soluble Y-shaped units can occur individually as monomers, or in complexes of two to five units.
Antibodies are glycoproteins belonging to the immunoglobulin superfamily.
The terms antibody and immunoglobulin are often used interchangeably, though the term 'antibody' is sometimes reserved for the secreted, soluble form, i.e. excluding B-cell receptors.

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  1. T

    COVID Antibody from Common Cold reacts to COVID

    THIS POST TITLE IS MISLEADING. I paraphrased/lifted from the jpost. com article but did not read the research article. @Ygggdrasil graciously points out the error in post #3 below. Thanks...
  2. mktsgm

    Medical The Role of Antibodies in the Immune System: A Closer Look

    I have a doubt. It is said that antigens detected by macrophages and and Dendritic cells (by way of PAMPs and DAMPs) can initiate and mount an immune response, why antibodies need to be produced. Ok, antibodies opsonize the intruders. But then even without antibodies, the innate immune system...
  3. Ygggdrasil

    Medical What are the latest developments in the search for a cure for Ebola?

    This week, the US National Institutes of Health released an update on a trial in the Democratic Republic of the Congo comparing the effectiveness of two new antibody-based drugs (REGN-EB3 and mAb114) against existing treatments for Ebola (ZMapp and remdesivir). The trial was halted early...
  4. I

    The molecular switch from welcoming to attacking a pathogen?

    I watched many videos and read bunch of answers about this, but I was having a hard time finding an answer to this one point: What is the exact moment an organism realizes that it is under an attack? I understand that there might be a few different types of ways a body can react too. So far...
  5. D

    Antibodies against hormones of the own body

    Recently I came upon the description of medical tests for hormones like cortisole, or tyroid hormones like T3 and T4, which use polyclonal antibodies from hamsters, pigs, sheep or thelike. As far as I know, they are obtained by vacunating these animals and harvesting the antibodies from their...
  6. A

    Antibodies to test Microfludic device for antigen detection

    Hello. Sorry in advance for my ignorance, but I am looking for a reaction that will yield a colorimetric signal when an antigen and an antibody meet. Similar to a one-step ELISA. My plan was to use HRP-conjugated BSA and anti-BSA. Will this work, and in how many steps? Any kits out there for...
  7. G

    20% of Antibodies not specific?

    Nice little paper about properly validating your reagents: http://www.ncbi.nlm.nih.gov/pubmed/22361696Why is it in academia absolutely no one validates their reagents like antibodies while in industry it is absolutely required? Rather than admitting their results are due to nonspecific...
  8. W

    Does Every Species Have an Immune System?

    i was told that only mammals have(can produce by their own) antibody... then how abt other animals like reptile,bird n fish?? without antibody,how can those animals protect themselves against diseases??
  9. S

    My confusion with IgE antibodies and allergy?

    Hello everyone, There was a simple question given, where there was a bee sting on a guy and the question asked was what is the antibody involved. The answer is IgE. Now my question is when there is bee sting for the first time, why do we called it an allergic reaction. I mean for an allergy...
  10. B

    IGE Antibodies & Allergy Increase: Facts & Statistics

    How are IGE antibodies related to an increase of allergies in the world?
  11. B

    Are t-cell receptors antibodies?

    I read that t-cells have receptors on their surface which bind to antigens. Are these receptors antibodies or are antibodies molecules which float around freely and mark antigens that they happen to bind to so that t-cells can kill them?