Human biochem lecture 11

Lecture Overview

• Focus on the adaptive immune system

• Topics include antibody structure, function, interactions, and comparison between myoglobin and hemoglobin.

Immune System Components

Overview of Immunity

• Two main types of immune systems in vertebrates: innate and adaptive.

Innate Immunity

• Components include:

  • Skin and mucous membranes

  • Normal microflora

  • Phagocytic cells

  • Antimicrobial substances

• Provides immediate defense against pathogens.

Adaptive Immunity

• Composed of:

  • B cells: Produce antibodies and provide memory of past infections.

  • T cells: Present antigens and help eliminate pathogens.

  • Can adapt based on previous encounters with antigens.

Antibodies and their Production

Antibody Production Process

• B cells recognize antigens through immunoglobulin receptors on their surface.

• Activation occurs when:

  • Antigens are internalized and presented with MHC class II.

  • T helper cells recognize the MHC-antigen complex and secrete cytokines.

• B cells undergo clonal expansion, producing effector B cells (plasma cells) that secrete antibodies.

Functions of Antibodies

Importance of Antibodies

• Five key roles:

  1. Agglutination: Clumping of pathogens for easier phagocytosis.

  2. Neutralization: Block binding of pathogens to target cells.

  3. Opsonization: Enhancing phagocytosis through antibody coating.

  4. Activation of Complement: Initiates inflammatory responses leading to cell lysis.

  5. Binding of Effector Cells: Facilitating clearance of large antigens.

Antibody Response Types

Primary and Secondary Responses

• In primary response, immature B cells produce effector B cells (plasma cells).

• Upon re-exposure to the same antigen, memory B cells enable a quicker and stronger secondary response by producing more antibodies.

Antibody Structure

Basic Structure

• Composed of four protein chains:

  • Two heavy chains

  • Two light chains

• Bound together by di-sulfide bridges.

Variable and Constant Regions

• Each chain consists of a variable (V) region and a constant (C) region.

• Binding sites formed by the combination of V regions specific to epitopes.

Immunoglobulin Classes

Overview of Immunoglobulins

1. IgM: First response, large structure, effective in initiating the complement system.

2. IgG: Most abundant, crosses blood vessels and the placenta, binds antigens, and activates complement.

3. IgA: Present in secretions (saliva, tears), protects mucosal surfaces.

4. IgD: Found on B cell surfaces.

5. IgE: Involved in allergic responses, binds to mast cells.

Antibody-Antigen Interactions

Mechanism of Interaction

• Interactions occur via loops in the variable regions, which have unique shapes and charges that match specific antigens.

• Includes complementarity determining regions (CDRs) that interact with antigens based on size and charge.

Novel Antibody Generation

Mechanisms

1. Shuffling of Nucleic Acid Sequences: Generates unique combinations of heavy and light chain regions.

2. Mutations in CDR Loops: Higher mutation rates that enhance antigen interaction properties without altering the overall structure of antibodies.