B cells 1 lecture

Introduction to B-cells

  • B-cells are crucial components of the adaptive immune response, functioning alongside T-cells.

  • Purpose of lectures:

    • Today's focus: B-cell development and antibody types.

    • Tomorrow's focus: The role and function of antibodies in immunity.

  • Key learning objectives:

    • Understand B-cell functions and properties.

    • Explore processes of B-cell development and their specificity for antigens.

B-cell Development

  • Overview of Development

    • Develop in the bone marrow and lymph nodes.

    • Development involves multiple stages, with gradual maturation.

  • Stages of B-cell Development

    1. Stem Cells

      • Originate in the bone marrow.

    2. Pro-B Cells

      • First stage in B-cell development.

    3. Pre-B Cells

      • Intermediate stage where heavy chain rearrangement occurs.

    4. Immature B Cells

      • Express IgM on the surface, migrate to lymph nodes.

    5. Naive B Cells

      • Mature cells ready to respond to antigens.

    6. Mature B Cells

      • Can undergo class switching (change the type of antibody they produce).

Functions of B-cells

  • B-cells make antibodies, which are critical for immune responses.

  • They help identify pathogens and enhance immune responses via specificity.

  • Memory B-cells

    • Long-lived cells that provide rapid responses upon re-exposure to pathogens.

    • Result from activation during the initial immune response.

Differences Between Innate and Adaptive Immunity

  • Innate Immunity

    • Immediate response to pathogens, non-specific.

    • Lacks memory function.

  • Adaptive Immunity

    • Slow, specific response that takes days to weeks.

    • Creates immunological memory allowing for quicker re-responses in future infections.

Activation and Interaction with T-cells

  • B-cell activation is dependent on T-cell help, particularly in secondary lymphoid organs.

  • Role of T helper cells

    • Provide necessary signals (cytokines) for B-cell responses.

    • Facilitate communication between immune cells.

Antibody Production and Types

  • Antibodies are released into circulation, acting as effector molecules to combat pathogens.

  • Types of Antibodies

    • Immunoglobulin classes (IgG, IgM, IgA, IgD, IgE) performing different roles.

  • Functionality depends on the constant region of the antibody.

B-cell Receptors (BCR) and Antigens

  • B cells recognize antigens through their BCR, which is a membrane-bound form of antibodies.

  • Unlike T-cells, B-cells can bind to soluble antigens and are not MHC-restricted.

Antibody Structure

  • Composed of:

    • Two Heavy Chains

    • Two Light Chains

    • Variable Regions for antigen binding

    • Constant Regions determine the antibody class

  • Hyper-variable regions (CDRs) are crucial for specificity in antigen binding.

Genetic Diversity and Recombination

  • Diversity of BCR and antibodies results from gene rearrangement during development:

    • Heavy chain rearrangement occurs first.

    • Followed by light chain rearrangement.

  • Mechanisms include:

    • Junctional diversity adds further variation.

    • Each B-cell expresses a unique BCR that recognizes different antigens.

Negative Selection and Tolerance

  • Negative selection occurs in the bone marrow to prevent self-reactive B cells from maturing:

    • B cells that recognize self-antigens can be deleted or undergo receptor editing.

    • Resulting in anergy for those that are not strongly activated but still self-reactive.

Conclusion on B-cell Maturation and Function

  • Summary of B-cell journey:

    • Starts in bone marrow, involves several stages of development and maturation.

    • Final stages occur in periphery after leaving bone marrow.

  • Importance of B-cells in establishing long-term immunity and the overall function of the adaptive immune system.