Antigen

An antigen (Ag) is a molecule or molecular structure, such as may be present at the outside of a pathogen, that can be bound to by an antigen-specific antibody (Ab) or B cell antigen receptor (BCR). The presence of antigens in the body normally triggers an immune response. The term "antigen" originally described a structural molecule that binds specifically to an antibody only in the form of native antigen,It was expanded later to refer to any molecule or a linear molecular fragment after processing the native antigen that can be recognized by T-cell receptor (TCR). BCR and TCR are both highly variable antigen receptors diversified by somatic V(D)J recombination. Both T cells and B cells are cellular components of adaptive immunity. The Ag abbreviation stands for an antibody generator.

Antigens are "targeted" by antibodies. 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 or matching 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 due to an adaptation in a region of the antibody; because of this, many different antibodies are produced, each able to bind a different antigen while sharing the same basic structure. In most cases, an adapted antibody can only react to and bind one specific antigen; in some instances, however, antibodies may cross-react and bind more than one antigen.

Also, an antigen is a molecule that binds to Ag-specific receptors, but cannot necessarily induce an immune response in the body by itself.[3] Antigens are usually proteins, peptides (amino acid chains) and polysaccharides (chains of monosaccharides/simple sugars) but lipids and nucleic acids become antigens only when combined with proteins and polysaccharides.[4] In general, saccharides and lipids (as opposed to peptides) 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 antigen may originate from within the body ("self-antigen") or from the external environment ("non-self"). The immune system is supposed to identify and attack "non-self" invaders from the outside world or modified/harmful substances present in the body and usually does not react to self-antigens under normal homeostatic conditions due to negative selection of T cells in the thymus.

Vaccines are examples of antigens in an immunogenic form, which are intentionally administered to a recipient to induce the memory function of adaptive immune system toward the antigens of the pathogen invading that recipient.

[Chris-pilm]

Found your YouTube channel through an Instagram comment, this has got to be one of the most informative YouTube channels for biology I’ve ever seen. Thank you and keep up the good work!

[hansaworld]

This video explained this concept exactly the way needed to understand..thank you !!

[jameschem]

This explanation is just perfect and brief🎉

[bluewave]

Clear & concise easy to understand explanation for us med students short on study time TY

[مصطفىمصطفى-تضص]

Geneous bro thank you for explaining and summarising

[stuffvlogs]

Pta nhi kya kya padhaya others YouTuber ❤ ne, bahut time baad apka tarika samjh aaya sir

[rajipotnuru]

Thankyou so much sir... for sharing this most informative vedio which helps us to study in a simple way...🙏...it will be more useful for my exams.

[uzmajan]

Thank u sir.... Seems to b very helpful in future.... And nice explanation. Keep making videos...

[neethuem]

Super presentation thanku so much sir, 🙏

[hamadamash]

Thank you it’s very helpful and easy :)

[joeguidi]

Great work! I appreciate your clear and thorough approach to these videos! Thank you.

[AnkeetKumar]

Heptan Vs Adjuvant , clear it to me. ?

[s.r]

Sir pls upload more videos on immunology series lectures..🙏🙏🙏

[jenniferyoung]

30secs in and i'm already confused. it's not the lecturer...i'm just not wired to "get it". however, i do appreciate the video.

[shreyajadhav]

Why exogenous antigen doesn’t require take up ?

[esharajput]

Please upload antigen antibody interaction video as soon as

[gulshansen]

Please upload more videos on MHC-I and MHC II.
Love from India ♥️

[andianabando]

you teach very well, just be slower remember youtube is global so that international people will understand properly

[krp_leop_pradhan]

Great video but you talk too fast little hard to catch up with your speed, over all good

[SY]

grey seed color in peas is dominant over white. In following experiment parents with known phenotype but unknown genotype produced following progeny-
gray. white

gray×white. 82. 78
gray×white 0. 50
gray×white. 74. 0
gray × white. 90 0

using G for gray and g for white give genotype of each parent.

plzz sir if possible answer the question in comment section. pllzzz.