Crossword clues for antigen
Longman Dictionary of Contemporary English
Douglas Harper's Etymology Dictionary
"substance that causes production of an antibody," 1908, from German Antigen, from French antigène (1899), from anti- (see anti-) + Greek -gen (see -gen).
n. (context immunology English) A substance that induces an immune response, usually foreign.
n. any substance (as a toxin or enzyme) that stimulates the production of antibodies
In immunology, an antigen is a molecule capable of inducing an immune response on the part of the host organism, though sometimes antigens can be part of the host itself. In other words, an antigen is any substance that causes an immune system to produce antibodies against it. Each antibody is specifically produced by the immune system to match an antigen after cells in the immune system come into contact with it; this allows a precise identification of the antigen and the initiation of a tailored response. The antibody is said to "match" the antigen in the sense that it can bind to it thanks to adaptations performed to a region of the antibody; because of this, many different antibodies can be produced, with specificity to bind many different antigens while sharing the same basic structure. In most cases, an antibody can only bind one specific antigen; in some instances, however, antibodies may bind more than one antigen.
In summary an antigen is a molecule that binds to Ag-specific receptors, but cannot necessarily induce an immune response in the body by itself. Antigens are usually peptides, polysaccharides or lipids. In general, molecules other than peptides (saccharides and lipids) qualify as antigens but not as immunogens since they cannot elicit an immune response on their own. Furthermore, for a peptide to induce an immune response (activation of T-cells by antigen-presenting cells) it must be a large enough size, since peptides too small will also not elicit an immune response. The term antigen originally described a structural molecule that binds specifically to an antibody. It expanded to refer to any molecule or a linear molecular fragment that can be recognized by highly variable antigen receptors ( B-cell receptor or T-cell receptor) of the adaptive immune system.
The antigen may originate from within the body ("self-antigen") or from the external environment ("non-self"). The immune system usually does not react to self-antigens under normal homeostatic conditions due to negative selection of T cells in the thymus and is supposed to identify and attack only "non-self" invaders from the outside world or modified/harmful substances present in the body under distressed conditions.
Antigen presenting cells present antigens in the form of peptides on histocompatibility molecules. The T cells of the adaptive immune system recognize the antigens. Depending on the antigen and the type of the histocompatibility molecule, different types of T cells are activated. For T-Cell Receptor (TCR) recognition, the peptide must be processed into small fragments inside the cell and presented by a major histocompatibility complex (MHC). The antigen cannot elicit the immune response without the help of an immunologic adjuvant. Similarly, the adjuvant component of vaccines plays an essential role in the activation of the innate immune system.
An immunogen is a substance (or adduct) that is able to trigger a humoral and/or cell-mediated immune response. It first initiates an innate immune response, which then causes the activation of the adaptive immune response. An antigen binds the highly variable immunoreceptor products ( B-cell receptor or T-cell receptor) once these have been generated. All immunogen molecules are also antigens, although the reverse is not true.
At the molecular level, an antigen can be characterized by its ability to bind to an antibody's variable Fab region. Different antibodies have the potential to discriminate among specific epitopes present on the antigen surface. A hapten is a small molecule that changes the structure of an antigenic epitope. In order to induce an immune response, it needs to be attached to a large carrier molecule such as a protein. Antigens are usually proteins and polysaccharides, and less frequently, lipids. This includes parts (coats, capsules, cell walls, flagella, fimbrae, and toxins) of bacteria, viruses, and other microorganisms. Lipids and nucleic acids are antigenic only when combined with proteins and polysaccharides. Non-microbial non-self antigens can include pollen, egg white and proteins from transplanted tissues and organs or on the surface of transfused blood cells. Vaccines are examples of antigens in an immunogenic form, which are intentionally administered to induce the memory function of adaptive immune system toward the antigens of the pathogen invading the recipient.
Usage examples of "antigen".
A survivor was important because he or she would have developed an antibody to combat the virus, or antigen.
According to one view, a hole is poked in the receptor membrane, launching depolarization, but other workers believe that the substance may become bound to the cells possessing specific receptors for it and then may just sit there, somehow displaying its signal from a distance, after the fashion of antigens on immune cells.
Proteins in Retroviral Vectors: Implications for Major Histocompatability Complex Antigen Activity.
Induction of oral tolerance in splenocyte recipients toward pretransplant antigens ameliorates chronic graft versus host disease in a murine model.
Anything that stimulates the production of antibodies is called an antigen.
So this was a free clinic and they screwed up the test and I came up positive with surface antigens and hepatitis.
Squark, the Wabble Effect, the Antigens, his own Theory of Subsequence.
Therefore, down on cellular level, your white blood corpuscles and antigens are waging relentless, violent war on invaders.
However, the lab boys tell me all body fluids contain antigens that indicate the blood type for that person.
Proteins in Retro-viral Vectors: Implications for Major Histocompatability Complex Antigen Activity.
The human body attacks embedded foreign objects through sophisticated immune reactions: inflammatory responses, antigens, macrophages, lymphocytes, fibroblasts.
What she had done instead was identify the short string of amino acids, peptides, that folded up to form the actual antigen of the viral protein, map out the amino acid sequence, and then bio-facture a combination of different peptides, matching different regions of the viral protein, in the hope that one or more of the synthetic peptides would fold up to mimic an antigenic site present on the viral protein.
The function of these molecules is to pick up bits of material inside a cell, peptides or antigens.
Valda laughed just behind him again, and she laughed harder when he tried to explain the work he had been doing on particlesdescribing the Squark, the Wabble Effect, the Antigens, his own Theory of Subsequence.
I've brought in plague antigens from Tampa, and I'm having serums made up from avirulent strains flown in right now from Los Angeles.