BY 312 Lecture (4/1)

HIV and AIDS Overview

  • The essay will focus on HIV and AIDS.

Antibody Classes

Overview

  • There are five classes of antibodies that play critical roles in immune response.

IgG (Immunoglobulin G)

  • Most numerous antibodies: Comprise 80% of total antibodies.

  • Function: Provides long-term immunity, crosses placenta, enhances phagocytosis, neutralizes toxins, and aids in complement activation.

  • Clinical Note: Refer to Table 22.3 for a summary of antibody classes.

IgM (Immunoglobulin M)

  • First antibody to appear during an immune response, secreted by plasmacytes upon initial exposure to an antigen.

  • Role: Important for activating complement, agglutinating microbes, and lysis of pathogens.

  • Short-lived: Initial response quickly wanes.

IgA (Immunoglobulin A)

  • Binding Sites: Four antigen binding sites.

  • Location: Found in body secretions (sweat, tears, saliva, breast milk, GI fluids).

  • Proportion: Comprises about 10-15% of antibodies in blood.

  • Impact of Stress: Levels decrease during stress, lowering resistance to infection.

IgE (Immunoglobulin E)

  • Prevalence: Very scarce, accounting for 0.1% of total antibodies.

  • Involvement: Participates in allergic reactions. Found on mast cells and basophils.

IgD (Immunoglobulin D)

  • Prevalence: Comprises 0.2% of all antibodies.

  • Function: Role in the activation of B cells, although not entirely understood.

Monoclonal Antibodies

  • Monoclonal antibodies (MABs) are hybrid antibodies produced in the lab with identical functions.

Production Process

  • Fusion: B cells are fused with tumor cells, providing rapid growth of identical antibodies.

  • Clinical Applications:

    • Diagnose drug levels in patients' blood.

    • Diagnose diseases: e.g., strep throat, allergies, pregnancy, cancer.

    • Aid in tissue graft acceptance and help prevent rejection.

Complement System

  • Definition: A series of blood proteins that work with antibodies to enhance immune function.

  • Activation: Complement can be activated via multiple pathways, typically in a cascading fashion, encouraging various immune responses like vasodilation, inflammation, antigen optimization, and lysis.

  • Main Proteins: C1 through C9 are the primary complement proteins.

    • C3b: Significant for enhancing phagocytosis and initiating the activation of the complement pathway.

Activation Pathways

  1. Classical Pathway: Triggered when an antibody binds to an antigen.

  2. Alternative Pathway: Activated by the interaction between complement proteins and lipid-carbohydrate complexes.

  3. Lecithin Pathway: Initiated by macrophages digesting microbes, which release chemicals activating C3.

Membrane Attack Complex (MAC)

  • Function: Forms as a result of complement cascade activation, leading to cell lysis.

Immunological Memory

  • Definition: The immune system's ability to remember past infections through memory cells.

  • Primary Response: Characterized by a slow increase in antibody titer after the first exposure, followed by gradual decline.

  • Secondary Response: Accelerated and more robust response upon subsequent exposures, with a quicker rise and longer-lasting antibodies.

Immunocompetence

  • Natural Immunity vs. Artificial Immunity:

    • Natural: Gained without medical intervention.

    • Artificial: Gained through modern medical practices such as vaccinations.

Types of Immunity

  1. Natural Active Immunity: Body produces antibodies after contracting a disease (e.g., hepatitis A).

  2. Natural Passive Immunity: Antibodies transferred from mother to child (breast milk).

  3. Artificial Active Immunity: Immune response triggered by vaccination.

  4. Artificial Passive Immunity: Injection of preformed antibodies (e.g., monoclonal antibodies).

Immunological Surveillance

  • Concept: The immune system continuously recognizes and removes cancer cells.

  • Mechanism: Tumor antigens are targeted by cytotoxic T cells, macrophages, and natural killer cells.

Immunotherapy

  • Definition: Therapy using the body's immune system to fight diseases, particularly cancer.

  • Types:

    • Cancer vaccines help the immune system fight specific cancer cells.

    • Adaptive cellular therapy boosts T cell effectiveness against cancer.

    • Cytokine therapy utilizes cytokines to combat cancer cells.

Aging and the Immune System

  • Changes with Age:

    • Atrophy of the thymus gland leading to increased T helper cell populations but diminished immune responses.

    • Increased incidence of cancer and autoimmune diseases in elderly individuals due to a compromised immune system.

HIV/AIDS

Overview of HIV

  • Definition: Human immunodeficiency virus, a retrovirus with two RNA strands and specific enzymes (protease, integrase, reverse transcriptase).

  • Capsid and Envelope: Comprised of a protein coat and a lipid bilayer with glycoproteins.

Transmission

  • Modes: Blood, semen, vaginal secretions, and breast milk.

  • Nonsexual contact does not transmit the virus.

  • Intravenous drug users are particularly at high risk.

Symptoms and Progression

  • Initial Symptoms: Flu-like symptoms (fever, fatigue, rashes) usually appear three to four weeks post-infection.

  • Progression to AIDS: Gradual, typically 2-10 years, characterized by enlarged lymph nodes, persistent night sweats, and susceptibility to opportunistic infections.

Treatment

  • Medications:

    • Reverse transcriptase inhibitors.

    • Integrase inhibitors.

    • Protease inhibitors.

    • Fusion inhibitors.

  • Pre-exposure Prophylaxis (PrEP): Antiviral medication for individuals at high risk of contracting HIV, taken daily.

  • Post-exposure Prophylaxis: Treatment for those exposed to HIV.

Allergic Reactions

  • Types of Allergic Reactions:

  1. Type I: Anaphylactic reactions.

  2. Type II: Cytotoxic reactions due to antibodies.

  3. Type III: Immune complex reactions involving antibodies and complement.

  4. Type IV: Cell-mediated (delayed hypersensitivity) reactions occurring 12-72 hours post-exposure.