AP Biology: Immune System Structure, Function, and Defense Mechanisms

Importance of the Immune System

Essential for defending the body against pathogens and abnormal cells.

Leukocytes

White blood cells crucial for identifying and eliminating pathogens.

Lymphocytes

A type of leukocyte involved in targeting cancer cells and abnormal body cells.

First Line of Defense

Physical and chemical barriers like skin and secretions that prevent pathogen entry.

Phagocytic White Blood Cells

White blood cells, such as neutrophils and macrophages, that engulf and destroy pathogens.

Neutrophils

The most abundant type of WBC with a short lifespan, crucial for quick immune response.

Natural Killer (NK) Cells

Specialized leukocytes that target and destroy virus-infected and cancerous cells.

Perforin

A protein released by NK cells that forms pores in target cell membranes, causing cell lysis.

Complement System

A group of approximately 20 proteins that enhance the immune response by attacking pathogens.

Antibodies

Proteins produced by B cells that bind to antigens and neutralize or mark them for destruction.

Primary Immune Response

The initial response of the immune system upon first exposure to a pathogen.

Secondary Immune Response

A quicker and stronger immune response upon re-exposure to the same pathogen.

Acquired Immunity

A specific defense mechanism involving B cells and T cells responding to specific antigens.

T Cells

Cells crucial for cell-mediated immunity, responding to infected and cancerous cells.

Blood Type Classification

Classification based on antigens present on the surface of red blood cells (A, B, AB, O).

HIV

A virus that targets Helper T cells, leading to immune system impairment and increased infection susceptibility.

Autoimmune Diseases

Conditions where the immune system mistakenly attacks the body's own tissues.

Functions of the Immune System

Defense against pathogens, removal of dead cells, and immune surveillance against abnormal cells.

Innate Immunity

Non-specific defense system present from birth, acting as the first line of defense.

Adaptive Immunity

Specific defense system that remembers past encounters with pathogens, involving B and T cells.

Pathogen

Any disease-causing agent, such as bacteria, viruses, fungi, or parasites.

Antigen

A molecule, often a protein or carbohydrate, that elicits an immune response.

Bone Marrow

The primary site of production for most immune cells, including leukocytes.

Thymus

An organ where T lymphocytes mature and undergo selection processes.

Lymph Nodes

Small, bean-shaped organs that filter lymph and are sites where immune cells interact and activate.

Spleen

An organ that filters blood, removes old red blood cells, and houses lymphocytes for immune responses.

Monocytes

A type of leukocyte that circulates in the blood and differentiates into macrophages upon entering tissues.

Macrophages

Large phagocytic cells found in tissues that engulf pathogens and present antigens.

Eosinophils

Leukocytes involved in combating parasitic infections and allergic reactions.

Basophils

Leukocytes that release histamine and other mediators during allergic and inflammatory responses.

Dendritic Cells

Antigen-presenting cells that capture antigens in tissues and transport them to lymph nodes to activate T cells.

Mast Cells

Immune cells found in connective tissues that release histamine and other inflammatory mediators, crucial in allergic reactions.

Humoral Immunity

The type of adaptive immunity mediated by B cells and their antibodies circulating in body fluids.

Cell-Mediated Immunity

The type of adaptive immunity mediated by T cells that directly attack infected cells or coordinate other immune cells.

Helper T Cells (CD4^+ T cells)

T cells that activate B cells, cytotoxic T cells, and other immune cells by releasing cytokines.

Cytotoxic T Cells (CD8^+ T cells)

T cells that directly recognize and kill cells infected with viruses or cancerous cells.

Memory B Cells

Long-lived B cells that remain in the body after an infection, providing rapid and strong response upon re-exposure.

Memory T Cells

Long-lived T cells that provide enhanced and faster cell-mediated immune responses upon re-encountering a specific antigen.

Immunoglobulins (Ig)

Another name for antibodies, produced by plasma cells (activated B cells).

Opsonization

The process by which pathogens are coated with opsonins (e.g., antibodies, complement proteins) to enhance phagocytosis.

Agglutination

The clumping together of antigens, often caused by antibodies binding to multiple antigens, making them easier for phagocytes to clear.

Inflammation

A protective response characterized by redness, swelling, heat, and pain, aimed at eliminating harmful stimuli and initiating healing.

Cytokines

Small proteins secreted by immune cells that act as chemical messengers to regulate immune responses and cell communication.

Major Histocompatibility Complex (MHC)

A complex of genes that encode proteins (MHC molecules) on cell surfaces, crucial for antigen presentation to T cells.

MHC Class I

MHC molecules found on almost all nucleated cells, presenting endogenous antigens to cytotoxic T cells.

MHC Class II

MHC molecules found primarily on antigen-presenting cells, presenting exogenous antigens to helper T cells.

AIDS (Acquired Immunodeficiency Syndrome)

The final, life-threatening stage of HIV infection, characterized by severe immune system damage and susceptibility to opportunistic infections.