STRUCTURE
Antigens are substances that can trigger an immune response in the body. They can be components of pathogens (like bacteria or viruses), foreign proteins, or even parts of our own cells that are recognized as abnormal. The structure of antigens varies widely because they can be virtually anything that the immune system can recognize as foreign. However, here are some common characteristics of antigens:
- Proteins and Glycoproteins: Many antigens are proteins or glycoproteins, which are proteins with attached carbohydrate molecules. These include viral proteins, bacterial cell surface proteins, and some allergenic proteins
- Carbohydrates: Some antigens are carbohydrates or glycolipids, like those found on the surface of bacteria or the ABO blood group antigens on red blood cells.
- Peptides and Epitopes: Antigens often contain specific regions called epitopes or antigenic determinants. These are the parts of the antigen that the immune system recognizes and responds to. These epitopes can be quite small, typically comprising around 5-15 amino acids for protein antigens.
- 3D Structure: Antigens have a specific three-dimensional structure that is recognized by antibodies or T cell receptors. This structure is critical for the immune system to identify them.
- Pathogen-Associated Molecular Patterns (PAMPs): Pathogens, like bacteria, often have specific molecular patterns on their surface called PAMPs. These are recognized by pattern recognition receptors (PRRs) on immune cells, and they act as antigens that can trigger an immune response.
- Haptens: Some antigens are too small to elicit an immune response on their own. These small molecules, known as haptens, can become antigenic when they bind to larger carrier molecules in the body.
The diverse nature of
antigens reflects the wide array of potential threats the immune system may
encounter. When the immune system encounters an antigen, it produces antibodies
(in the case of B cells) or activates T cells to recognize and eliminate the
foreign invader. The immune system's ability to recognize and respond to
antigens is crucial for defending the body against infections and maintaining
overall health.
1.
Is it possible that an
antigen stays on your own body cells?
- Yes, your body's cells contain antigens. These antigens are proteins that your immune system learns to see as normal and usually does not react against.
- A healthy immune system tolerates self-antigens and does not attack them. Self-antigens are antigens that the immune system derives from the body it is protecting. For example, a heart cell, a liver cell, and a kidney cell would all contain self-antigens.
- Antigens are any substance that induces the immune system to produce antibodies against it. Any foreign invaders, such as pathogens (bacteria and viruses), chemicals, toxins, and pollens, can be antigens.
- When antibodies attach to an antigen, it signals other parts of the immune system to attack and destroy the invaders. After they're made, antibodies usually stay in our bodies in case we have to fight the same germ again.
DIVERSITY/TYPES OF ANTIGENS:
Antigens are incredibly
diverse and can encompass a wide range of substances that can trigger an immune
response. The diversity of antigens is critical because it allows the immune
system to recognize and respond to a broad spectrum of potential threats. Here
are various types of antigens based on their sources and characteristics:
1. Microbial Antigens:
- Bacterial Antigens:
These include components of bacterial cell walls, like
lipopolysaccharides, peptidoglycans, and proteins.
- Viral Antigens:
These comprise proteins and glycoproteins on the surface of viruses, as
well as viral genetic material.
- Fungal Antigens:
Antigens from fungi can be found in their cell walls, spores, and other
structural components.
- Parasite Antigens:
Parasitic organisms, such as protozoa and helminths, have antigens on
their surfaces and within their bodies.
2. Allergens:
- Allergens are antigens that trigger
allergic reactions. Common allergens include pollen, dust mites, pet dander,
and certain foods.
3. Autoantigens:
- Autoantigens are self-antigens,
meaning they are derived from the body's own tissues. In autoimmune
diseases, the immune system mistakenly recognizes autoantigens as foreign
and mounts an immune response against them.
4. Haptens:
- Haptens are small molecules that, on
their own, cannot trigger an immune response. However, when they bind to
larger carrier molecules, they become antigenic. Common examples include
certain drugs and chemicals.
5. Blood Group
Antigens:
- Blood group antigens determine an
individual's blood type. The ABO and RhD blood group systems are
well-known examples of blood group antigens.
6. Tumor Antigens:
- Tumor antigens are specific to cancer
cells. They can be altered or mutated proteins that the immune system may
recognize as abnormal and target for destruction.
7. Vaccine Antigens:
- Vaccines contain inactivated or
weakened forms of pathogens or pieces of pathogens that stimulate the
immune system to produce a response. These components serve as vaccine
antigens.
8. Food Antigens:
- Certain food proteins can act as
antigens. In some cases, the immune system may mount responses against
these food antigens, leading to food allergies.
9. Plant Antigens:
- Pollen, plant proteins, and other
components can trigger allergic reactions in individuals with plant
allergies.
10. Environmental
Antigens:
- Environmental antigens include
substances like dust, mold spores, and animal dander. Exposure to these
antigens can lead to allergic responses.
11. Drugs and
Medication Antigens:
- Some drugs and medications can act as
antigens, leading to hypersensitivity reactions in individuals who are
sensitive to them.
The immune system's
ability to recognize and respond to such a diverse array of antigens is
fundamental to its role in protecting the body from infections, maintaining
immune tolerance, and managing autoimmune reactions. The specificity and
diversity of the immune response are vital for overall health and immune
function.