immunity

Immunity Overview

• Defenses
    - Two main types:
      - Innate Immunity (Non-specific defenses)
      - Adaptive Immunity (Specific defenses)

Innate Immunity

• Types of Defenses
    - External:
      - Skin
      - Exoskeleton (in arthropods)
      - Mucous membranes
      - Cilia
      - Secretions (antimicrobial)
    - Internal:
      - Phagocytic cells
      - Natural killer (NK) cells
      - Antimicrobial proteins
      - Inflammatory response

Characteristics of Innate Immunity

• Barrier Defenses:
    - Cuticle in arthropods
    - Mucous membranes in molluscs
    - Presence of antimicrobial compounds
    - Involvement of Toll-like receptors (TLRs), produced by:
      - Fungi
      - Plants
      - Animals

Non-specific Cellular Defenses

• Cell Types Involved:
    - Granulocytes (polymorphonuclear leukocytes):
      - Neutrophils (60-70% of white cells)
      - Eosinophils (2-5% of white cells)
      - Basophils (0.5% of leukocytes)
      - Mast Cells: Participate in tissue inflammation
    - Phagocytic White Blood Cells:
      - Monocytes (5% of white cells)
      - Convert into macrophages upon arriving at sites of infection

Inflammatory Response

• Triggered by damaged tissues when:
    - Damage occurs (e.g., bacteria enter)
    - Initial bleeding initiates clotting by platelets
    - Cells release cytokines at the site of injury
    - Mast cells degranulate, releasing histamines
    - Neutrophils actively phagocytize foreign material
    - Monocytes arrive and mature into macrophages, aiding in tissue repair

Adaptive Immunity

• Main Features:
    - Involves lymphocytes:
      - B-cells (produce antibodies)
      - T-cells

• Antigen Recognition and Immunological Memory:
    - Development of self vs. non-self recognition through:
      - Major Histocompatibility Complex (MHC) molecules:
        - Class I MHC (binds to cytotoxic T-cells)
        - Class II MHC (binds to helper T-cells)

Mechanism of Antigen Presentation

• Process:
    1. Antigen ingestion through phagocytosis
    2. Digestion of antigen proteins into fragments
    3. Binding of fragments to MHC II molecules in endosomes
    4. Transport of MHC complex to plasma membrane
    5. Presentation of antigen fragment at the cell surface

• Antigen Receptors: Each cell has a specific type of receptor.
    - B-cells (plasma cells and memory B-cells)
    - T-cells (helper - CD4+ and cytotoxic - CD8+)

• Epitopes: Specific parts of antigens recognized by antibodies.

Mechanisms of Antibodies

• Functions of Antibodies:
    - Enhance phagocytosis (opsonization)
    - Neutralize toxins
    - Lead to cell lysis by activating complement system

Types of Adaptive Immune Responses

• Humoral Immunity:
    - Effective against:
      - Bacteria
      - Viruses
      - Toxins present in body fluids

• Cell-Mediated Immunity:
    - Effective against:
      - Infected cells
      - Cancerous cells

Clonal Selection and Memory Response

• Clonal Selection: After activation, lymphocytes divide to produce:
    - Plasma cells
    - Memory B-cells
    - Memory T-cells

• Primary Immune Response: First exposure takes 10-17 days for full formation of antibodies.

• Secondary Immune Response: Quicker and stronger response due to immunological memory (memory B-cells and T-cells) that responds to subsequent exposures.

Vaccination and Immunization

• Types of Vaccines:
    - Subunit Vaccines: Include pieces of the pathogen.
    - Inactivated Vaccines: Contain killed pathogens.
    - Attenuated Vaccines: Weakened pathogens.
    - mRNA Vaccines: E.g., SARS-CoV-2 mRNA vaccines (Moderna, Pfizer) that use synthetic mRNA to produce spike proteins.
    - Important components of mRNA vaccines include:
      - Methylated guanine cap
      - Poly-A tail
      - Coding and non-coding sequences

Covid Vaccines

• Types of Covid Vaccines:
    - Viral Vector Vaccines: E.g., Oxford-AstraZeneca (Covishield), Johnson & Johnson
    - mRNA Vaccines: E.g., Moderna, Pfizer

ABO Blood Groups and Genetics

• Types of Blood Groups:
    - A, B, AB, O

• Alleles:
    - IA (A antigen)
    - IB (B antigen)
    - i (no antigen)

• Specific Genetic Combinations:
    - A: IAIA or IAi
    - B: IBIB or IBi
    - AB: IAIB
    - O: ii

Rh Factor

• Relates to the presence of an antigen on a transmembrane protein, likely an ion channel.

• Alleles and Their Products:
    - IA allele gene product
    - IB allele gene product
    - i allele gene product

Organ Transplants and Related Immunology

• Transplant Types:
    - Living-related
    - Cadaveric

• Considerations for Successful Transplants:
    - MHC testing to ensure compatibility
    - ABO matching required
    - Good HLA match across three MHC loci (best match is a score of 6)

Allergies and Inappropriate Immune Responses

• Allergies: Inappropriate reaction to an antigen (allergen).

• Involve IgE antibodies that bind to mast cells and basophils.

• Both genetic and environmental factors contribute to allergic reactions.

• Severe Allergy Response: Anaphylaxis or anaphylactic shock can result from extreme immune responses.