Comprehensive Guide to Immunology

What are Antigens and Antibodies, and how do they function?

Antigens trigger immune responses; antibodies are proteins produced by B cells to specifically recognize and neutralize them. This fundamental interaction in adaptive immunity allows the body to combat foreign invaders. Antibodies bind to specific epitopes on antigens, marking them for destruction or directly neutralizing their effects, forming a crucial defense.

• Immunogenicity vs. Antigenicity: Inducing response vs. binding.
• Antibody Structure: Heavy/light chains, CDRs, Fc/Fab regions.
• Epitope Definition: Specific binding sites, sequential or conformational.

How are Immunoglobulin Genes Organized and Expressed?

Immunoglobulin gene organization and expression involve unique genetic mechanisms generating vast antibody diversity. This ensures the immune system recognizes an immense array of antigens, crucial for adaptive immunity. Processes like V(D)J recombination and somatic hypermutation create a diverse repertoire of antibodies, enabling specific recognition.

• V(D)J Recombination: Random gene segment assembly for diversity.
• Somatic Hypermutation: Introduces point mutations for affinity maturation.
• Allelic Exclusion: Ensures B cells express only one antibody type.
• Antibody Engineering: Creating chimeric or humanized antibodies.

What defines Antigen-Antibody Interactions and how are they measured?

Antigen-antibody interactions are highly specific binding events crucial for immune recognition and pathogen neutralization. Characterized by affinity and avidity, these determine binding strength. Various techniques quantify these associations, providing insights into immune responses and aiding in diagnostic and therapeutic development.

• Affinity vs. Avidty: Strength of single bond vs. overall binding.
• Experimental Techniques: ELISA, Western Blot, Surface Plasmon Resonance (SPR).

What is the Complement System and how does it protect the body?

The complement system, part of innate immunity, is a cascade of proteins enhancing immune response. It clears pathogens, promotes inflammation, and directly lyses target cells. Activation pathways form membrane attack complexes, which perforate microbial membranes. Its regulation prevents damage to host cells.

• Activation Pathways: Classical, Alternative, and Lectin.
• MAC Formation: Membrane Attack Complex for cell lysis.
• Regulation: Inhibitors prevent uncontrolled activation.

What is the Major Histocompatibility Complex (MHC) and its role?

MHC molecules are cell surface proteins vital for presenting antigens to T lymphocytes. Class I presents endogenous antigens to cytotoxic T cells; Class II presents exogenous antigens to helper T cells. This is fundamental for adaptive responses, allowing T cells to recognize and respond to infected or foreign cells.

• MHC Class I: Presents endogenous antigens.
• MHC Class II: Presents exogenous antigens.
• Antigen Presentation: Crucial for T lymphocyte activation.

What is the T Cell Receptor (TCR) and how does it function?

The T Cell Receptor (TCR) on T lymphocytes recognizes specific antigen fragments presented by MHC molecules. Its precise gene rearrangement generates immense diversity, enabling T cells to detect threats and initiate responses. TCR signaling, aided by coreceptors, ensures specific and effective immune activation.

• Gene Rearrangement: Creates diverse TCR repertoire.
• TCR-CD3 Complex Signaling: Transmits antigen recognition.
• Coreceptors (CD4, CD8): Enhance TCR signaling and specificity.

How do T Lymphocytes Mature, Activate, and Differentiate?

T lymphocytes mature in the thymus, undergoing positive and negative selection for self-tolerance and functionality. Activated by antigen-presenting cells, they differentiate into various subtypes, orchestrating immune responses. These subtypes include helper, cytotoxic, and regulatory T cells, each with distinct roles in immunity.

• Thymic Selection: Positive and negative selection.
• T Lymphocyte Subtypes: Helper (Th), Cytotoxic (Tc), Regulatory (Treg).
• Cytokine Secretion: Mediates communication and immune regulation.

How are B Lymphocytes Generated, Activated, and Differentiated?

B lymphocytes are generated in bone marrow, forming BCRs and undergoing negative selection. Activated, often in germinal centers, they differentiate into plasma cells or memory B cells, providing humoral immunity. Plasma cells secrete antibodies, while memory cells ensure a faster, stronger response upon re-exposure.

• BCR Formation: B cell receptors and negative selection.
• Germinal Center Reactions: B cell proliferation and affinity maturation.
• Differentiation: Plasma cells (antibody production) and memory B cells.

What are Cytokines and what is their function?

Cytokines are small proteins acting as crucial messengers in the immune system, facilitating communication between immune cells. They regulate immune responses, inflammation, and hematopoiesis. Cytokine profiles dictate the type of immune response, influencing whether it's primarily cell-mediated or humoral, maintaining immune balance.

• Immune Cell Communication: Mediators of intercellular signaling.
• Th1/Th2 Balance: Influences cell-mediated vs. humoral immunity.

How do Leukocytes Activate and Migrate within the body?

Leukocyte activation and migration are essential for immune surveillance. White blood cells activate from pathogens or tissue damage, then use adhesion molecules and chemokines to migrate into infected tissues, targeting threats. This directed movement ensures immune cells reach sites of inflammation or infection promptly.

• Adhesion Molecules & Chemokines: Guide leukocyte movement.
• Inflammation & Tissue Homing: Direct leukocytes to sites of need.

What are Cytotoxic Reactions and how do they eliminate target cells?

Cytotoxic reactions eliminate infected or cancerous cells. CTLs, NK cells, and ADCC employ distinct strategies to induce apoptosis or lysis in target cells, ensuring effective immune surveillance. These mechanisms are vital for controlling viral infections and preventing tumor growth, protecting the host.

• Target Cell Elimination: Mechanisms include perforin/granzyme, death receptor pathways.

What is the difference between Innate and Adaptive Immunity?

Innate immunity is the body's immediate, non-specific first line of defense, lacking memory. It includes barriers, phagocytes, and complement. Adaptive immunity is highly specific, develops memory, and improves with exposure, involving T and B lymphocytes for targeted, long-lasting protection. Both systems collaborate to provide comprehensive defense.