Antigens and their Properties

Antigens and their Important Properties

 

Abstract:

Antigens are molecules or molecular structures that are recognized by the immune system as foreign or non-self. They play a central role in the body’s immune response. An antigen should be an immunogen to initiate an immune response in the body. The immune system recognizes self-antigens from foreign. Antigenicity is species-specific and exhibits individual differences in its level of response.

1. Foreign Invaders: Antigens are typically found on the surface of pathogens such as bacteria, viruses, and fungi. They can also be present on foreign substances like pollen, toxins, or transplanted tissues.
2. Immune Recognition: When the immune system encounters antigens, specialized cells called immune cells, including T cells and B cells, recognize these molecules as foreign invaders.
3. Immune Response: Recognition of antigens triggers an immune response. The immune system’s goal is to eliminate or neutralize the foreign substance, which may involve the production of antibodies (by B cells), activation of T cells, and other immune processes.
4. Specificity: Antigens are highly specific. Each antigen is recognized by a particular set of immune cells or antibodies that are tailored to that specific antigen. This specificity allows the immune system to target different pathogens and foreign substances selectively.
5. Memory: After the immune system encounters an antigen, it can “remember” it. This memory response is the basis of immunity. If the same antigen is encountered in the future, the immune system can mount a faster and more effective response to eliminate it.

Types of Antigens:

1. Pathogen-Associated Molecular Patterns (PAMPs): These are specific molecular patterns found on the surface of pathogens, such as bacterial cell wall components or viral proteins. PAMPs are recognized by pattern recognition receptors (PRRs) on immune cells, initiating an immune response.
2. Epitopes: Epitopes, also known as antigenic determinants, are specific regions or structures on antigens that are recognized by antibodies or T-cell receptors. Epitopes can be linear (consecutive amino acids) or conformational (formed by folding of the antigen).
3. Autoantigens: Some antigens are part of the body’s own tissues. When the immune system mistakenly recognizes these self-antigens as foreign, it can lead to autoimmune diseases, where the immune system attacks its own tissues.
4. Allergens: Allergens are antigens that trigger allergic reactions. Common allergens include pollen, dust mites, certain foods, and insect venom. Allergic individuals produce an exaggerated immune response to these antigens.

Antigen Presentation:

Antigens are presented to immune cells through a process called “antigen presentation”, which involves specialized cells known as antigen-presenting cells (APCs). APCs, such as dendritic cells, macrophages, and B cells, capture, process, and display antigens on their cell surfaces. This presentation allows T cells to recognize antigens and initiate immune responses, humoral and Cell-mediated Immunity.

Haptens

Haptens are small molecules that are not antigenic on their own but can become antigenic when they bind to carrier proteins or larger molecules. Haptens are responsible for some types of allergic reactions, as they can induce immune responses when attached to larger proteins.

Adjuvants

Pharmacologically or immunologically an adjuvant is an agent that modifies the effect of other agents such as haptens. Normally, haptens are with poor immune responses due to low molecular weight (usually <1000 Daltons) and are rapidly removed from the body. Initiation of proper immune response requires an antigen with at least 8000-10000 Daltons Molecular weight. To prevent this, first, the poor antigen has to be combined with an adjuvant for the immune response against the antigen and maximise the immune response before the body clears the antigen.

Vaccination:

Vaccination involves exposing the immune system to harmless antigens (usually parts of pathogens or weakened pathogens) to stimulate an immune response without causing disease. This primes the immune system to recognize and remember the antigens, providing immunity when the real pathogen is encountered.

Antigens in Transplants:

In organ transplantation, the recipient’s immune system recognizes the transplanted tissue as foreign due to differences in antigens. Matching certain key antigens, particularly in the major histocompatibility complex (MHC), is crucial to reduce the risk of rejection.

Antigens and Cancer:

Tumour cells often display abnormal antigens or increased levels of certain antigens. Immunotherapy strategies aim to target these cancer-specific antigens to stimulate the immune system to attack and eliminate cancer cells.

Conclusion:

Antigens are central to the functioning of the immune system and its ability to distinguish between self and non-self. Understanding how antigens are recognized and processed is essential in the fields of immunology, vaccine development, organ transplantation, and cancer immunotherapy.