Antigen and pathogen are crucial components of our bodies’ immunity. They also play an important role in microbiology. A pathogen is a disease-causing organism, whereas an antigen is a substance that can activate an immune response. Pathogens include bacteria, viruses, and other microorganisms. Antigens are proteins, polysaccharides, or lipids present on the surface of pathogens. Antigens discovered on pathogens are known as exogenous antigens.
Other types of antigens include endogenous antigens, autoantigens, and neoantigens. Pathogens employ specialised methods in order to evade immune responses and survive and reproduce within the host. We’ll go through distinctions, attributes, types, and structures in depth in this article.
Antigen
Antigen is a substance that stimulates an immune response by activating lymphocytes, the body’s infection-fighting white blood cells. Foreign antigens (heteroantigens) and autoantigens are two types of antigens (self-antigens).
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Antigens that come from outside the body are known as foreign antigens.
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On the other hand, autoantigens are produced by the body itself.
Autoantibodies are produced in reaction to normal physiological substances, and the body can discern the difference between self and non-self. Normal physiological substances, on the other hand, activate an immune response in patients with autoimmune illnesses, resulting in the creation of autoantibodies.
Antigen Properties
The following are some of the features of antigens:
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Foreignness confers the ability to recognise and distinguish between self and non-self-molecules. Non-self-molecules provoke an immunological response, but self-molecules do not.
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Immunogenic molecules are massive and complicated, with a molecular weight of 10,000. Non-immunogenic immunogens, such as amino acids, are relatively small, whereas weak immunogens are weakly immunogenic. Haptens become immunogenic when they are combined with a carrier protein.
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Antigens, as opposed to short simple peptides with just a few epitopes, must have a certain level of chemical complexity and a structure with a high number of antigenic determinants (epitopes) in order to activate an immune response.
Types of Antigen
Antigens are mainly classified as
Based on Their Origin
Exogenous Antigens
Exogenous antigens are those that come from somewhere other than the host’s body and are hence alien to the host. These antigens can enter the body via inhalation, ingestion, or injection, and then circulate throughout the body via bodily fluids.
Autoantigens
Autoantigens are proteins or protein complexes that the host’s immune system attacks, resulting in autoimmune disease. So because the immune system should not assault the body’s own cells, autoantigens can be fatal to the host. Immune tolerance to such antigens is lost as a result of inherited and environmental causes.
Native Antigens
Native antigens are antigens that have not been processed by any antigen-presenting cells (APC), hence immune cells like T-cells can’t bind to them, but B-cells can.
Based On Immune Response
Complete Antigens
Complete antigens or immunogens are antigens that elicit a specific immune response. These antigens can elicit an immune response even if no carrier particles are present.
In complete Antigens
Incomplete antigens, also known as haptens, are antigens that cannot generate an immune response by themselves. These are mainly non-protein molecules that need a carrier molecule to function as a complete antigen.
Structure of Antigen
Antigen can bind to an antibody’s antigen-binding site.
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Antibodies discriminate between antigens based on the molecular structures located on the surface of the antigen.
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Antigens are mostly made up of proteins and polysaccharides. Bacteria, viruses, and other microorganisms have coats, capsules, flagella, toxins, and fimbriae, for example. Antigens can also be found in secretions and other related substances.
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Lipids and nucleic acids from these bacteria are only antigenic when combined with proteins or polysaccharides.
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Antigens can take on a number of forms depending on the composition, size, and immunogenicity of the antigen.
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All immunogenic antigens contain an epitope, also known as an antigenic determinant.
Pathogen
A pathogen is an organism that causes disease. These germs are only a problem if your immune system is weakened or if they enter a normally sterile area of your body. To thrive and survive, a pathogen requires a host.
Once inside a host’s body, the pathogen avoids immune responses and replicates with the body’s resources before escaping and spreading to a new host. Depending on the infection, it can spread by skin contact, body fluids, airborne particles, faeces contact, and contacting a surface that has been touched by a sick person.
Properties of Pathogen
The primary purpose of pathogens is to live and reproduce in their host. To survive, they must find a nutrient-rich biological component that is acceptable for them. Pathogens are adept at analysing a cell’s processes and evolving to exploit their hosts.
Types of Pathogen
Viruses
Viruses are made up of a little piece of genetic information (DNA or RNA) encased in a protein sheath. Once you’ve been infected, they infect host cells in your body and reproduce using the host cell’s components to produce more viruses. Once the replication cycle is complete, the new viruses are ejected from the host cell. As a result, the sick cells are commonly injured or destroyed.
Some viruses can remain dormant for long periods of time before reactivating. When this happens, a person appears to have recovered from a viral infection only to fall unwell again.
Bacteria
They may live in a variety of environments, including within and on your body, and they come in a variety of shapes and sizes. Bacteria do not all cause infections. You may be more susceptible to bacterial infections if your immune system has been weakened by a virus.
Microorganisms that are usually harmless can become hazardous as a result of a virus-caused disease. Antibiotics are antibiotics that are used to treat bacterial infections. Several bacterial strains have developed antibiotic resistance, making treatment challenging.
Fungi
There are millions of different fungus species in the world. Only roughly 300 of them are known to be harmful. Fungi can be found practically anywhere, both inside and outside buildings, as well as on people’s skin. They spread illness when they outgrow their bounds.
A membrane and a thick cell wall protect the nucleus and other components of fungus cells. Because of their structure, they are more difficult to destroy.
Parasites
These bacteria live in or on a host, feeding on or causing harm to the host. Although parasitic infections are more common in tropical and subtropical areas, they can occur worldwide.
Differences between Antigen and Pathogen
| Antigen | Pathogen |
| This is a type of Molecule. | Generally Pathogen is an infectious agent. |
| Antigens include lipids, peptides, and polysaccharides, are the examples. | Pathogens include viruses, fungi, bacteria, and other microorganisms. |
| This can come from both biological and non-biological Sources. | Biological pathogens such as bacteria and fungi are common in this. Non-living Things are also included in it. |
Conclusion
Pathogens can make us sick, but when we’re healthy, our bodies are capable of fighting them and the illnesses they bring. Antigen is a foreign substance or toxin that causes the body’s immune system to respond by producing antibodies.
Antigens found in the body’s own cells are called self-antigens, and the immune system usually ignores them. Antibodies are proteins made by the body to help it fight antigens, which are foreign substances. Antibodies attach to antigens and bind to them, leaving them inactive.