Adaptive Immune System and Its Mechanisms

Overview of the Adaptive Immune System

  • The adaptive immune system differs from the innate immune system, which is static and does not change over time.

  • The innate immune system provides fixed strategies: barriers, lysozymes, phagocytes, and antimicrobial peptides.

  • Selection pressure can influence evolution in pathogens (e.g., bacteria evolving resistance to antibiotics).

Inflammation and Sensitive Skin

  • Inflammation is related to the adaptive immune response, particularly in cases of sensitive skin.

  • Sensitive skin often reacts to bacteria as if they are harmful, leading to inflammation, red and swollen areas, and sometimes acne.

  • Histamine is a key player in this process, as it causes blood vessels to expand and become more permeable.

  • Cutting the skin through shaving can introduce bacteria, triggering an immune response and inflammation.

Acne as an Allergic Response

  • Acne can be viewed as an allergic response to skin bacteria.

  • Treatments often focus on suppressing the immune response or using antihistamines.

  • Antihistamines in shave creams could alleviate inflammation, though they are seldom included in these products.

Evolutionary Dynamics of the Immune System

  • Adaptive immunity adapts and responds to pathogens more efficiently than the innate system.

  • Bacteria evolve quickly (every 20-30 minutes), while humans have a generation time of 20-30 years, leading to a constant battle.

  • The immune system evolves by generating cell types that can target these rapidly evolving pathogens.

Evolving Immunity via Variation

  • The adaptive immune system generates a variety of immune cells with different receptors based on proteins found in pathogens, which allows for effective targeting.

  • Cells that can recognize and bind to a new threat multiply and persist in the body, allowing for rapid responses in the future.

Mechanism of Immune Recognition

  • Immune cells recognize pathogens through receptors that bind to specific proteins known as antigens.

  • Proteins are fundamental to all biological structures; immune cells can bind to them to recognize threats.

Concept of Antigens

  • An antigen signals an immune response if recognized by the immune system.

  • For example, the A antigen is present in blood type A; blood type O does not produce it, making blood type O universal donors due to lack of reaction.

  • COVID-19 recognition occurs through a specific spike protein on the virus.

Immune Cell Differentiation: T-Cells and B-Cells

  • The immune system generates B and T cells that are crucial for adaptive immunity.

  • B Cells: Develop in the bone marrow, can directly recognize pathogens, produce antibodies, and create memory cells.

  • T Cells: Mature in the thymus, require antigen presentation via MHC molecules for activation.

Antibody Functionality

  • Antibodies are unique receptors that can neutralize pathogens by binding to antigens.

  • They prevent viruses from infecting cells by blocking their entry mechanisms.

Distinction Between Helper T-Cells and Cytotoxic T-Cells

  • Helper T-Cells (CD4+): Activate B-cells and other immune cells; require MHC II for antigen presentation.

  • Cytotoxic T-Cells (CD8+): Kill infected or cancerous cells; require MHC I for antigen recognition.

  • Both types of T-cells replicate once activated, generating an aggressive immune response when needed.

The Role of Vaccines

  • Vaccines present antigens without fully introducing the pathogens, allowing the immune system to create a memory without causing illness (e.g., using mRNA to prompt protein production).

  • Vaccines prepare the immune system to respond rapidly to future infections.

Immune Memory and Response Strength

  • Upon first exposure to a pathogen, immune response develops and ramps up slowly; memory cells enable quicker responses to subsequent infections.

  • Initial reactions lead to the generation of both memory and effector T-cells, which remain ready to deploy if re-exposed to the same pathogen.

Allergies and the Immune System

  • Allergies are caused by inappropriate immune responses to harmless substances (e.g., peanuts, pollen).

  • The first exposure does not elicit a strong response, while subsequent exposures trigger severe reactions due to pre-formed mast cell receptors for the allergen.

Antivenom Production

  • Antivenom treatments involve the use of antibodies raised in other animals (e.g., horses) after injecting them with venom. Antibody-rich serum is extracted and used to counteract venom effects.

HIV and Immune Evasion

  • HIV specifically targets CD4 T-cells, crippling the immune response by evading detection and destruction due to helper T-cells being essential for other immune functions.

  • Some people are resistant to HIV due to mutations in the CCR5 receptor, rendering them impervious to the virus.