Introduction to Antibodies

• Antibodies are crucial for various applications and research in immunology.

Antibody Applications

• Secondary Antibody Conjugation
    - Secondary antibodies are often conjugated to enzymes, which catalyze reactions.
    - Example: Use of fluorescent substrates that indicate the presence of specific proteins.
• Fluorescence in Protein Detection
    - Fluorescence indicates the presence of a target protein in cells.
    - Useful for observing protein expression in processes like metastasis.

Monoclonal Antibodies

• Definition
    - Monoclonal antibodies are generated to recognize a single epitope of a protein.
• Production Method
    - A protein of interest (e.g., protein x) is injected into a mouse.
    - This stimulates the mouse's B cells to produce antibodies against that protein.
    - B cells are fused with cancer cells to form hybridomas, which can proliferate indefinitely and produce large quantities of antibodies.
• Selection Process
    - Rigorous testing ensures that antibodies bind only to the specific epitope of interest, allowing for the elimination of non-specific antibodies.

Clinical Applications of Monoclonal Antibodies

• T Cell Targeting
    - Monoclonal antibodies (e.g., targeting CD3 positive T cells) are used to reverse kidney transplant rejection.
    - Tissue transplants are perceived as foreign by the immune system, inducing an immune response against them.
• Etanercept (Etuximab)
    - A monoclonal antibody that neutralizes TNF-alpha, a cytokine involved in inflammation.
• General Function of Antibodies
    - Antibodies specifically target antigens or proteins of interest, enabling targeted treatment in various diseases, including cancer.

Immune Response Dynamics

• Primary Immune Response
    - Upon first exposure to an antigen, the body produces antibodies, plasma cells, and memory cells.
    - Example of this process seen with vaccinations: the body generates a response to a harmless version of a pathogen.
• Secondary Immune Response
    - Following re-exposure to an antigen (as in booster shots), memory cells enable a quicker and more potent antibody response.
• Function of Vaccines
    - Vaccines introduce a harmless antigen sequence into the body, prompting the immune system to develop antibodies for future protection against the actual pathogen.

Types of Immunity

• Active Immunity
    - Acquired through exposure to infections or vaccination, leading to the body generating specific antibodies.
• Passive Immunity
    - Temporary immunity through the introduction of antibodies from one individual to another (e.g., maternal antibodies passed through breast milk).

Immune System Mechanisms

Endogenous and Exogenous Pathways

• Endogenous Pathway
    - Involves cells processing their own proteins (damaged or viral) to present on MHC Class I molecules, activating CD8 (cytotoxic) T cells.
• Exogenous Pathway
    - Involves antigen-presenting cells engulfing outside pathogens (like bacteria) and presenting their fragments on MHC Class II molecules, activating CD4 (helper) T cells.

Immune Cell Activation

• Process
    - Infected cells signal for help by presenting antigen fragments on MHC molecules to T cells; this activates the T cells, leading to clonal expansion.
• Role of Cytotoxic T Cells
    - Cytotoxic T cells target and destroy virus-infected cells by secreting perforins that create holes in the target cell membranes.

Importance of Antigen Presenting Cells (APCs)

• APCs
    - Dendritic cells and other APCs engulf pathogens and present antigens to T cells, playing a crucial role in activating the adaptive immune response.
• Self vs. Non-Self Recognition
    - All nucleated cells present MHC class I molecules, indicating their health status, while APCs communicate signals to T cells regarding pathogens.

Pathologies and Immune Malfunctions

• Overactive Immune Responses
    - Conditions like multiple sclerosis involve the immune system mistakenly targeting healthy cells.
    - HIV primarily targets CD4 T cells, impairing the immune response by limiting B cell activation and antibody production.
• Viral Persistence
    - Some viruses integrate their genetic material into host DNA, like herpes, leading to periodic viral reactivation.

Inhibitory Signals in the Immune System

• Cellular Communication
    - Healthy cells communicate with immune cells to prevent unwanted immune responses against themselves.
    - Malfunctions can lead to excessive immune activation, resulting in conditions such as allergies and anaphylaxis due to histamine release.

Conclusion

• Immunology encompasses various mechanisms for disease detection, prevention, and treatment focusing on antibodies, T cell activation, and the immune system's overall functioning.