Immune System and Lymphocyte Functionality

Introduction

  • Question about the characteristics that differentiate self from non-self in the context of the immune system

Immune System Recognition

  • Self vs. Non-Self:
    • The immune system distinguishes between self and non-self based on chemical structures of molecules.
    • Plasma proteins in the blood are crucial for this identification.
    • Body recognizes the unique chemical structure of these proteins.
    • If plasma proteins leak into tissues, it could compromise the integrity of the blood.
  • Immune Cell Recognition:
    • Immune cells, such as T lymphocytes and B lymphocytes, are not inherently intelligent in their initial recognition of pathogens.
    • Role of Macrophages:
    • Macrophages engulf pathogens, analyze and digest them, and break them down into smaller units.
    • They release enzymes from lysosomes during this process.
    • The resulting fragments are checked against the body’s own chemical structures.
      • If the fragments are unfamiliar, they trigger an immune response.

Activation of T Lymphocytes

  • Pathogen Recognition Process:
    • After macrophages process a pathogen, they show the T lymphocyte small, non-familiar chemical fragments.
    • T lymphocytes only become active after recognizing these unfamiliar structures either directly or through help from B lymphocytes and macrophages.

Allergic Reactions

  • Anticipated Reactions:
    • Examples: Allergic reactions to mangoes or chocolates occur because the body recognizes chemical structures in these foods as antigens, leading to an immune response.

Histocompatibility in Organ Transplants

  • Histocompatibility Testing:
    • The body's recognition of foreign tissues is crucial for organ transplants.
    • Tests are performed on potential donor organs to see if their antigens match the recipient's.
    • If there is a recognition reaction, the transplant is likely to fail as the body will attack and break down the new organ.

Types of Immune Cells

  • Antigen-Presenting Cells:
    • Specific macrophages that present antigens after digesting pathogens.
    • Key role in activating the immune response.

Non-Antigenic Molecules

  • Some molecules may not be antigenic on their own but can become antigenic after binding with larger molecules within the body, becoming known as haptens.
    • Haptens can provoke an immune response once modified.

Origin and Production of Lymphocytes

  • Production Sources:
    • Lymphocytes are produced primarily in the red bone marrow.
    • Myelogenic Origin:
    • Refers to blood cells originating from the bone marrow, called myelo in medical terms, and also refers to the spinal cord.
  • Differentiation of Cells:
    • Unspecialized lymphocytes released into the bloodstream.
    • Divided Production:
    • Approximately 50% are directed to the thymus for further development into T lymphocytes.
    • The remaining 50% circulate as immature B lymphocytes.

Development of T and B Lymphocytes

  • T Lymphocytes in Thymus:
    • Specialization occurs in the thymus, where T lymphocytes grow and develop further, becoming crucial for immune defense.
  • B Lymphocytes in Blood:
    • B lymphocytes and T lymphocytes make up around 70-80% and 20-30% of circulating lymphocytes, respectively.

Adaptive Immune Response

  • Activation Requirements:
    • T lymphocytes must be activated by antigen fragments presented on antigen-presenting cells before responding to an antigen.
    • This activation occurs when the T cell encounters an antigen displaying cell like a macrophage.
  • Cytokines’ Role:
    • Once activated, T lymphocytes produce cytokines that enhance the immune response.
    • Cytokines are critical for stimulating B cell activity and the overall immune response.

Functions of T Cells

  • Helper T Cells:
    • Activate B cells to produce antibodies.
  • Cytotoxic T Cells:
    • Directly attack and kill infected or cancerous cells.
  • Memory T Cells:
    • Recognize pathogens during subsequent exposures, facilitating faster responses.
  • Regulatory T Cells:
    • Regulate the intensity of the immune response to prevent overreaction once the infection is managed.

Impact of Immune System on Diseases

  • Cancer Resistance:
    • Healthy immune systems may inhibit cancer progression, illustrated by differing survival rates in patients with similar cancers depending on their immune system's strength.
  • AIDS and HIV:
    • HIV targets T lymphocytes, compromising the immune system and leading to AIDS, characterized by severely weakened immune responses.

Memory Cell Formation

  • Memory Cells in Immune Response:
    • Memory T and B cells quickly respond to previously encountered pathogens, requiring less time than initial responses.
    • This capacity is a significant feature of adaptive immunity, enhancing efficiency in responding to infections.
  • Difference Between Primary and Secondary Immune Responses:
    • Primary Response: Takes 10-15 days due to the body's need to identify and develop a response to the antigen.
    • Secondary Response: Takes 1-3 days, as memory cells respond much faster upon re-exposure to the same antigen.

B Lymphocyte Functionality

  • B Cells Activation:
    • Activated through binding of antigens to their specific receptors, leading to clonal expansion into plasma and memory cells.
    • Monoclonal Antibodies:
    • Produced by differentiated B lymphocytes, play a crucial role in targeted immune responses.