Body Defenses and Immune System Notes

Immunity

• Defined as the body's ability to resist or eliminate harmful invaders or abnormal cells.

Functions of the Immune System

• Defend against pathogens (invading bacteria and viruses).
• Remove worn-out cells and damaged tissues.
• Immune surveillance: identify and destroy abnormal cancer cells originating in the body.

Major Targets of the Immune System

• Pathogenic bacteria and viruses.
• Virulence: the disease-producing ability of a pathogen.

Leukocytes (White blood cells)

• The main effector cells in the immune system.
• Types include neutrophils, eosinophils, basophils, monocytes, and lymphocytes.

Lymphoid Tissues

• Organ sites for lymphocyte production, storage, or processing (e.g., lymph nodes, spleen).
• Other leukocytes originate from bone marrow stem cells.

Types of Immune Responses

• Innate (Non-specific): Immediate response to foreign material (e.g., inflammation).
• Adaptive (Specific): Customized responses targeting specific invaders, involving B and T lymphocytes.

Components of Innate Immunity

1. Inflammation:

• A non-specific response to tissue injury involving phagocytic cells.

1. Interferon:

• Proteins that defend against viral infections through viral replication interference.

1. Natural Killer Cells:

• Lymphocyte-like cells that destroy virus-infected and cancer cells.

1. Complement System:

• Plasma proteins that attack and destroy foreign cells by disrupting their membranes.

Process of Inflammation

• Activated resident macrophages begin phagocytosis of foreign microbes.
• Vasodilation allows increased blood flow and leukocyte emigration.
• Increased capillary permeability leads to localized edema.
• Walling off injured regions to prevent spread and marking bacteria for destruction.
• Mediated by cytokines, leading to tissue repair.

Chronic Inflammation

• Occurs when the triggering agent persists, relevant to various chronic diseases (e.g., atherosclerosis, asthma).
• NSAIDs and glucocorticoids can suppress inflammation.

Interferon's Role

• Produced in response to viral attacks; warns neighboring cells to prepare against viruses and enhances NK cell activity.

Natural Killer Cells and the Complement System

• NK cells destroy infected or cancerous cells through membrane disruption.
• The complement system promotes cell lysis through the formation of the membrane attack complex.

Adaptive Immunity

• Antibody-Mediated (Humoral): B lymphocytes produce antibodies against foreign invaders.
• Cell-Mediated: T lymphocytes attack unwanted cells directly.
• B and T lymphocytes originate from stem cells in bone marrow; differentiation is site-dependent (thymus for T cells).

Antigen Definition

• A molecule that triggers an immune response, specifically antibody generation by B lymphocytes.
• B lymphocytes can respond to T-independent or T-dependent antigens.

Antibody Characteristics

• Y-shaped molecules; specific to unique antigens; consists of heavy and light chains.
• Effector mechanisms include complement activation, phagocytosis promotion, and NK cell activation.

Clonal Selection Theory

• Proposes that diverse B cells are produced before exposure to antigens.
• B cells differentiate into plasma cells (secreting antibodies) and memory B cells (for rapid response to future exposures).

Types of Immunity

• Active Immunity: Body produces its own antibodies post-exposure.
• Passive Immunity: Temporary immunity is gained through pre-formed antibodies.

T Lymphocytes

• Bind directly to their targets when the right antigen-MHC complex is displayed.
• Types include cytotoxic T cells (destroy infected cells) and helper T cells (enhance immune activity).

MHC and Transplant Rejection

• MHC molecules must be recognized for immune system interaction; mismatches can lead to rejection.

Autoimmunity

• Loss of self-tolerance which can lead to autoimmune diseases (lupus, rheumatoid arthritis).

Cancer and Immune Surveillance

• T cells recognize and destroy potentially cancerous cells to prevent disease progression.

Immunodeficiency Diseases

• Result from insufficient immune responses; examples include severe combined immunodeficiency, which is life-threatening without a sterile environment.

Allergies

• Hypersensitive immune responses against typically harmless substances, varying from mild to severe reactions.