Understanding the Immune System

• The immune system is the body's defense against disease-causing agents like bacteria, viruses, and parasites.
• This system is a complex network of cells and organs that protect the body from infection.
• A key role of the immune system is identifying and eliminating abnormal cells.
• Immunity is the defense capacity of the body to combat diseases and counter infection.

Immune System Production Sites

• Bone Marrow produces all immune cells, including B cells, T cell precursors, macrophages, neutrophils, eosinophils, basophils, dendritic cells, natural killer cells, and mast cells.
• B cells mature in the bone marrow.
• Natural Killer (NK) Cells attack virus-infected and cancer cells without prior activation.
• Mast cells play a key role in allergic reactions and inflammatory responses.
• Thymus serves as the maturation site for T cell precursors from the bone marrow into CD4+ T helper cells and CD8+ cytotoxic T cells.

Secondary Lymphoid Organs

• These are the activation sites for immune responses

Lymph Nodes

• Lymph nodes filter pathogens and activate lymphocytes

Spleen

• Spleen filters blood and helps in immune cell activation

Mucosa-Associated Lymphoid Tissue (MALT)

• MALT includes Peyer's patches in the intestines, tonsils, and adenoids.
• MALT helps detect pathogens at mucosal surfaces.

Major Functions

• Defends against pathogens by identifying and eliminating harmful invaders like bacteria, viruses, fungi, and parasites.
• Removes damaged cells by clearing out dead or malfunctioning cells to maintain tissue health.
• Provides surveillance for abnormal cells by detecting and destroying cells that have become cancerous or mutated.
• Immune memory enables a faster and stronger response if the same threat surfaces again after an infection or vaccination.

Types of Immune System

• Innate Immunity is the body's first line of defense, present from birth, providing a general defense against pathogens without targeting specific ones.
• Innate immunity acts quickly to prevent infections and includes physical and chemical barriers, as well as certain immune cells
• Physical barriers in Innate Immunity: skin and mucous membranes
• Chemical defenses in Innate Immunity: stomach acid and enzymes.
• Immune cells in Innate Immunity: macrophages, neutrophils, natural killer cells.
• Innate immunity triggers inflammation and fever to fight infections.
• Acquired (Adaptive) Immunity is specific.
• B-Cell Immunity consists of B cells, which produce antibodies and are involved with primary and secondary responses.
• T-Cell Immunity consists of T cells, including T helper cells and T killer cells.

Acquired Adaptive Immunity

• Active Immunity: body produces its own antibodies after infection or vaccination.
• Passive Immunity: antibodies are received from another source, e.g., maternal antibodies from breast milk or antibody injections.

Lymphatic System

• A network of vessels that transport lymph, a fluid containing white blood cells and waste.

Lymph Nodes

• Small structures that filter lymph and trap harmful substances.

Thymus

• Filters blood, removes damaged cells, and produces immune cells.

Spleen

• An organ that produces and matures T-cells for immune defense.