Introduction to Pathophysiology and Immunity

Introduction to Pathophysiology/Immunity

• Pathophysiology is the study of the disordered physiological processes associated with disease or injury.
• Immunity is the body's ability to resist or eliminate potentially harmful foreign substances (pathogens) or abnormal cells.
• Immune system dysfunction can lead to various diseases, including autoimmune disorders and immunodeficiencies.

Key Components of the Immune System

• Innate Immunity: This is the first line of defense, acting quickly and non-specifically against a wide range of pathogens.
  • Physical barriers (skin, mucous membranes)
  • Chemical mediators (e.g., complement system, cytokines)
  • Cellular components (e.g., macrophages, neutrophils, natural killer cells)
• Adaptive Immunity: This is a more specific and sophisticated response, developing over time and tailored to a particular pathogen.
  • Humoral immunity (antibodies produced by B lymphocytes)
  • Cellular immunity (T lymphocytes, directly killing infected cells)

Innate Immune Response

• Inflammation: The hallmark of innate immunity, characterized by redness, swelling, heat, and pain.
• Phagocytosis: The process by which immune cells like macrophages engulf and destroy pathogens.
  • Recognizes pathogen-associated molecular patterns (PAMPs)
• Complement System: A cascade of proteins that enhances inflammation, directly kills pathogens, and promotes opsonization.
  • Opsonization: Marking pathogens for phagocytosis by immune cells.
  • Important in the activation of the adaptive immune system.

Adaptive Immune Response

• Antigen Recognition: Adaptive immune cells (lymphocytes) recognize specific foreign antigens presented by antigen-presenting cells (APCs).
  • APCs process and present antigens, crucial in initiating the adaptive response.
  • T lymphocytes and B lymphocytes are involved.
• B Cell Activation: B cells, upon recognition of an antigen, differentiate into plasma cells, which produce antibodies.
  • Antibodies bind to antigens, neutralizing them or promoting their elimination by other immune cells.
  • Memory B cells are produced for future immune responses.
• T Cell Activation: Activated by encountering antigen presented by APCs.
  • Helper T cells (Th cells) coordinate the immune response by releasing cytokines.
  • Cytotoxic T cells (Tc cells) directly kill infected cells.
  • Memory T cells are produced.

Immune System Dysfunction

• Autoimmune Diseases: The immune system mistakenly attacks the body's own tissues.
  • Examples: Lupus, rheumatoid arthritis, multiple sclerosis.
• Immunodeficiencies: A weakened or absent immune response, increasing susceptibility to infections.
  • Primary immunodeficiencies are congenital (present at birth).
  • Secondary immunodeficiencies develop later in life (e.g., due to HIV infection or cancer treatments).
• Hypersensitivity Reactions: Overreactions of the immune system, causing tissue damage.
  • Type I hypersensitivity (allergic reactions)
  • Type II hypersensitivity (cytotoxic reactions)
  • Type III hypersensitivity (immune complex diseases)
  • Type IV hypersensitivity (cell-mediated reactions)

Cellular Interactions in Immunity

• Cytokines: Signaling molecules released by immune cells to regulate and communicate with other immune cells.
  • Influence the activation, differentiation, and survival of immune cells.
  • Can affect inflammation and other aspects of the immune response.
• Lymphocyte trafficking: The movement of lymphocytes between tissues to recognize and respond to pathogens.
  • Essential for orchestrating the immune response.

Immune Responses to Infections

• Viral Infections: The immune system combats viral infections through cytotoxic T cell responses, neutralizing antibodies, and antiviral cytokines.
• Bacterial Infections: Antibodies, phagocytic cells, and complement are critical for combating bacterial infections.
• Fungal Infections: Both innate and adaptive immune responses are needed.

Immune System and Disease

• Cancer: The immune system plays a role in detecting and destroying abnormal cells.
  • Immunotherapy aims to enhance the body's own immune response to fight cancer.
• Organ Transplantation: The immune system recognizes transplanted organs as foreign and tries to reject them.
  • Immunosuppressants are given to prevent rejection.

Immune System Development and Maturation

• Lymphopoiesis: The development and maturation of lymphocytes in primary lymphoid organs (bone marrow and thymus).
• Lymphocyte receptors: Key components of immune recognition (TCRs and BCRs).

The Complement System in Immunity

• The complement system is a group of proteins that enhance the ability of antibodies and phagocytic cells to clear pathogens and damaged cells from an organism.
• The complement system has diverse mechanisms of action, including opsonization, chemotaxis, and cell lysis.
• The complement system also triggers inflammatory responses.
• Complement activation can be initiated through three pathways: classical, lectin, and alternative. Each pathway has different molecular triggers.