Antigens and Antibodies | Science & Technology for UPSC CSE PDF Download

Introduction

• Antigens: Antigens are foreign substances that can enter the body and trigger an immune response. These substances are usually harmful and include various pathogens such as bacteria, viruses, fungi, and other microorganisms. Antigens can also include non-microbial substances like allergens (e.g., pollen, dust mites) and even some components of transplanted organs. When antigens enter the body, they are recognized as foreign invaders, leading to an immune response aimed at neutralizing or eliminating them.
• Antibodies: Antibodies, also known as immunoglobulins (Ig), are glycoproteins produced by the immune system in response to the presence of specific antigens. Antibodies are highly specific and are designed to recognize and bind to particular antigens. They play a crucial role in the body's defense mechanism by targeting and neutralizing antigens. Antibodies can work in various ways, such as blocking the harmful effects of antigens, marking them for destruction by immune cells, or directly attacking and destroying the antigens.

Antigen

Antigens are substances or toxins that stimulate the body's immune system, triggering an immune response to fight against them. Here are some key points about antigens:

• Nature of Antigens: Antigens can be various types of substances, including bacteria, viruses, and other microorganisms. These foreign invaders are often the primary targets of the immune system's response. However, antigens can also include non-microbial substances like allergens (e.g., pollen), certain proteins in foods, and even components of venomous snake bites.
• Immune Response: When antigens enter the body, they are recognized as foreign and potentially harmful. This recognition initiates the body's immune response, which aims to neutralize or eliminate these antigens.
• Lymphocytes and Antibodies: Lymphocytes, a type of white blood cell, play a central role in the immune response to antigens. In response to antigens, lymphocytes produce specialized proteins called antibodies. These antibodies are designed to bind to specific antigens, marking them for destruction.
• Types of Antigens:
  • Heteroantigens: These are antigens that originate from outside the body and are foreign to the individual. Examples include viruses, bacteria, protozoa, and allergens. Blood transfusions from other people and certain proteins in foods can also introduce heteroantigens into the body.
  • Autoantigens: Autoantigens, also known as self-antigens, are produced by the body's own cells. They are typically recognized and targeted by the immune system in autoimmune conditions. In autoimmune diseases, the immune system mistakenly identifies the body's own cells and tissues as foreign invaders, leading to an immune response against these autoantigens.

Antibody

Antibodies, also known as immunoglobulins (Ig), are essential components of the immune system responsible for defending the body against pathogens and foreign invaders. Here are some key points about antibodies:

• Structure: Antibodies are Y-shaped proteins, and they are produced by a type of white blood cell called B lymphocytes or B cells. These proteins are highly specialized and designed to recognize and neutralize specific antigens.
• Function: Antibodies have several crucial functions in the immune response:
  • They bind specifically to antigens, which are foreign substances or pathogens.
  • Once bound to an antigen, antibodies can tag it for destruction by other immune cells, such as phagocytes.
  • Antibodies can neutralize toxins produced by bacteria or viruses, preventing them from harming the body's cells.
  • They can also block antigens from attaching to and infecting healthy host cells, thus inhibiting the spread of infection.
• Types of Antibodies: There are several main types of antibodies (immunoglobulins) in the body, each with its unique functions:
  • IgG: These antibodies are the most abundant in the bloodstream and provide long-term protection. They play a crucial role in detoxifying harmful substances and pathogens.
  • IgM: IgM antibodies are the first antibodies produced by B cells in response to an antigen. They are important in the early stages of infection.
  • IgA: IgA antibodies are found in mucosal membranes, saliva, tears, and other body fluids. They help collect antigens and remove them from the body, providing localized defense.
  • IgE: IgE antibodies are involved in allergic reactions and play a role in protecting against parasites. They are present in small amounts in the skin, lungs, and mucosal membranes.
  • IgD: IgD antibodies bind to B cells and play a role in signaling them to release IgM antibodies when needed.
• Diverse Roles: Each type of antibody has a specific function in the immune system, contributing to the body's defense against infections, toxins, and allergens. Their roles vary from providing rapid defense to long-term immunity.
• Distribution: Antibodies are found throughout the body, including in the bloodstream, mucosal surfaces, and other body fluids. They work collectively to protect against various threats.

Difference between Antigens and Antibodies

Difference between mRNA Vaccine and Traditional Vaccines

• Vaccines are a critical tool in preventing and controlling infectious diseases. Here's an explanation of how vaccines work and the difference between traditional vaccines and mRNA vaccines:

How Vaccines Work

• Training the Immune System: The primary goal of vaccines is to train the body's immune system to recognize and defend against disease-causing organisms, such as viruses or bacteria. When the immune system encounters a pathogen, it generates a targeted response to eliminate the threat.
• Introduction of Antigens: Vaccines contain substances known as antigens, which are typically proteins found on the surface of the pathogen. These antigens can be whole or inactivated pathogens, pieces of the pathogen (subunit vaccines), or, in the case of mRNA vaccines, genetic instructions to produce a specific viral protein.
• Immune Response: When a vaccine is administered, the immune system recognizes the antigens as foreign invaders. It then produces specific antibodies and activates immune cells to target and eliminate these antigens.
• Memory Cells: After the immune response, the body retains memory cells (memory B cells and memory T cells) that "remember" the specific pathogen's antigens. These memory cells allow the immune system to respond rapidly and effectively if the person is later exposed to the actual pathogen.

Traditional Vaccines

• Traditional vaccines use small or inactivated doses of the whole pathogen or specific proteins from the pathogen. These antigens are introduced into the body to stimulate an immune response. Examples include the measles, mumps, and rubella (MMR) vaccine and the hepatitis B vaccine.

mRNA Vaccines

• mRNA vaccines, such as the COVID-19 mRNA vaccines (Pfizer-BioNTech and Moderna), work differently. Instead of introducing antigens directly, they use a small piece of messenger RNA (mRNA) that encodes a viral protein.
• When the mRNA from the vaccine enters cells, it instructs the cells to produce a specific viral protein (usually a spike protein found on the virus's surface). This protein is harmless and cannot cause disease.
• The immune system recognizes this newly produced viral protein as foreign and mounts an immune response, generating antibodies and memory cells.
• In the future, if the person encounters the actual virus, their immune system is already prepared to recognize and fight it.

Functioning of mRNA Vaccines

• Synthetic mRNA Production: Scientists create a synthetic version of the mRNA (messenger RNA) that the virus uses to produce its infectious proteins. This synthetic mRNA is designed to encode a specific viral protein, often a harmless part of the virus, such as the spike protein found on the virus's surface.
• Delivery into the Human Body: The synthetic mRNA is delivered into the human body through vaccination. It can be encapsulated in lipid nanoparticles to protect it and facilitate its entry into human cells.
• Cellular Protein Production: Once inside the cells, the synthetic mRNA serves as instructions for the cells to produce the viral protein encoded by the mRNA. The cell's machinery reads this genetic information and starts assembling the viral protein.
• Formation of Viral Proteins, Not Virus: Importantly, the viral proteins produced are individual components and do not assemble to form a complete virus. This means that they cannot create a fully functional virus or cause disease.
• Immune System Activation: The immune system recognizes these viral proteins as foreign invaders, even though they are harmless fragments of the virus. In response, the immune system generates a defensive response, which includes the production of antibodies and the activation of immune cells.
• Memory Cells: As with traditional vaccines, mRNA vaccines also stimulate the production of memory cells (memory B cells and memory T cells). These memory cells "remember" the viral protein, providing long-lasting immunity.
• Protection Against Future Infections: If the vaccinated individual is later exposed to the actual virus, their immune system is prepared to recognize and mount a swift response against it. This helps prevent infection or reduces the severity of the illness.

Advantages of Using mRNA based Vaccines

• Safety: mRNA vaccines are considered safe because the mRNA used in these vaccines is non-infectious and non-integrating. It cannot alter the recipient's DNA or cause the disease it's meant to protect against. Additionally, mRNA is a transient molecule that is naturally degraded by cellular mechanisms once its job of protein synthesis is complete.
• High Efficacy: mRNA vaccines are highly efficacious due to their ability to instruct cells to produce the target viral protein directly in the cytoplasm. This prompts a robust immune response, including the production of antibodies and the activation of immune cells, leading to effective protection against the virus.
• Synthetic Nature: mRNA vaccines are fully synthetic, meaning they don't rely on the growth of infectious agents like viruses or bacteria. This is in contrast to some traditional vaccines that require the cultivation of viruses or bacteria in host organisms like eggs. Because mRNA vaccines are synthetic, they can be rapidly and inexpensively manufactured.
• Rapid Development: The technology used to create mRNA vaccines allows for accelerated vaccine development. Once the genetic sequence of a virus is known, scientists can quickly design and produce the corresponding mRNA vaccine. This rapid development capability proved crucial in responding to emerging infectious diseases like COVID-19.
• Accessibility: Because of their synthetic nature and efficient manufacturing process, mRNA vaccines have the potential to be widely accessible. This is especially important for global vaccination campaigns, as it enables the production of large quantities of vaccines to meet demand.