Human Anatomy and Physiology - The Immune System

Flashcards covering the key concepts of the immune system, including innate and adaptive defenses, cells of the immune system, and immune system pathology.

Immune System

Provides resistance to disease and pathogens.

First line of defense

External body membranes (skin and mucosae) provide a physical barrier.

Second line of defense

Antimicrobial proteins, phagocytes, and other cells inhibit the spread of invaders; inflammation is the most important mechanism.

Adaptive Immune System

Attacks particular foreign substances and has a memory.

First Line of Defense

Barriers that either do not allow pathogens into the body or purge them.

Phagocytes

Macrophages and neutrophils.

Inflammatory Response

Macrophages, mast cells, WBCs, and inflammatory chemicals.

Antimicrobial proteins

Interferons and complement proteins.

Inflammation

Triggered whenever body tissues are injured due to trauma, heat, irritating chemicals, or infections by microorganisms.

Benefits of Inflammation

Prevents spread of damaging agents, disposes of cell debris and pathogens, alerts adaptive immune system, and sets the stage for repair.

Four Cardinal Signs of Acute Inflammation

Redness, heat, swelling, and pain.

Pus

Creamy yellow mixture of dead neutrophils, tissue/cells, and living/dead pathogens.

Abscess

Collagen fibers are laid down, walling off the sac of pus; may need to be surgically drained.

Antimicrobial Proteins

Enhance innate defense by attacking microorganisms directly or hindering their ability to reproduce.

Interferons (IFN)

Family of immune modulating signaling proteins secreted by cells infected with viruses to warn healthy neighboring cells.

Complement System

Consists of ~20 blood proteins that circulate in the blood in inactive form and provides a major mechanism for destroying foreign substances.

Fever

Abnormally high body temperature that is a systemic response to invading microorganisms.

Phagocytes Protective Mechanism

Engulf and destroy pathogens that breach surface membrane barriers; macrophages also contribute to adaptive immune responses.

Natural killer (NK) cells Protective Mechanism

Promote apoptosis (cell suicide) by directly attacking virus-infected or cancerous body cells; recognize general abnormalities rather than specific antigens.

Inflammatory response Protective Mechanism

Prevents injurious agents from spreading to adjacent tissues, disposes of pathogens and dead tissue cells, and promotes tissue repair.

Interferons (a, B, y) Protective Mechanism

Proteins released by virus-infected cells and certain lymphocytes; act as chemical messengers to protect uninfected tissue cells from viral takeover; mobilize the immune system.

Complement Protective Mechanism

A group of bloodborne proteins that, when activated, lyse microorganisms, enhance phagocytosis by opsonization, and intensify inflammatory and other immune responses.

Fever Protective Mechanism

Systemic response initiated by pyrogens; high body temperature inhibits microbes from multiplying and enhances body repair processes.

Adaptive Immune System

A specific defensive system that eliminates almost any pathogen or abnormal cell in the body.

Characteristics of Adaptive Immunity

Recognizes and targets specific antigens, is systemic, and has memory.

Antigens

Substances that can mobilize adaptive defenses and provoke an immune response.

Immunogenicity

Ability to stimulate proliferation of specific lymphocytes.

Reactivity

Ability to react with activated lymphocytes and antibodies released by immunogenic reactions.

Self-Antigens

All cells are covered with a variety of proteins located on the surface that are not antigenic to self, but may be antigenic to others in transfusions or grafts.

Antigen-Presenting Cells (APCs)

Engulf antigens and present fragments of antigens to T cells for recognition.

Dendritic Cells

Found in connective tissues and epidermis; act as mobile sentinels of boundary tissues.

Macrophages

Widely distributed in connective tissues and lymphoid organs; present antigens to T cells, which not only activates T cells, but also further activates macrophages.

B LYMPHOCYTES Type of immune response

Humoral

T LYMPHOCYTES Type of immune response

Cellular

B LYMPHOCYTES Antibody secretion

Yes

T LYMPHOCYTES Antibody secretion

No

B LYMPHOCYTES Primary targets

Extracellular pathogens (e.g., bacteria, fungi, parasites, some viruses in extracellular fluid)

T LYMPHOCYTES Primary targets

Intracellular pathogens (e.g., virus-infected cells) and cancer cells*

B LYMPHOCYTES Site of origin

Red bone marrow

T LYMPHOCYTES Site of origin

Red bone marrow

B LYMPHOCYTES Site of maturation

Red bone marrow

T LYMPHOCYTES Site of maturation

Thymus

B LYMPHOCYTES Effector cells

Plasma cells

T LYMPHOCYTES Effector cells

Cytotoxic T (Tc) cells
Helper T (TH) cells
Regulatory T (Treg) cells

B LYMPHOCYTES Memory cell formation

Yes

T LYMPHOCYTES Memory cell formation

Yes

Humoral Immunity

When a B cell encounters a target antigen, it provokes a humoral immune response, and antibodies specific for that particular antigen are then produced.

B Cell Activation

B cells are activated when antigens bind to surface receptors, leading to proliferation and differentiation of the B cell into effector cells.

Antibodies (Immunoglobulins - Igs)

Proteins secreted by plasma cells and make up the gamma globulin portion of blood, capable of binding specifically with the antigen detected by B cells.

Primary Immune Response

Cell proliferation and differentiation upon exposure to an antigen for the first time.

Secondary Immune Response

Re-exposure to the same antigen gives a faster, more prolonged, and more effective response because sensitized memory cells provide immunological memory.

Active Humoral Immunity

Occurs when B cells encounter antigens and produce specific antibodies against them.

Passive Humoral Immunity

Occurs when ready-made antibodies are introduced into the body.

Cellular Immunity

Lymphocytes act against target cells directly by killing infected cells or indirectly by releasing chemicals that enhance the inflammatory response or activating other lymphocytes or macrophages.

Cellular Immune Response

T cells provide defense against intracellular antigens, such as cells infected with viruses or bacteria, cancerous or abnormal cells, or foreign (transplanted) cells.

Two Populations of Naive T cells

CD4 cells usually become helper T cells, and some become regulatory T cells, which moderate the immune response; can also become memory T cells.

Two Populations of Naive T cells

CD8 cells become cytotoxic T cells (TC) and also become memory T cells.

Role of Helper T Cells (TH)

Play a central role in adaptive immune response and activate both humoral and cellular arms.

Role of Cytotoxic T Cells (TC)

Directly attack and kill other cells, targeting virus-infected cells, cells with intracellular bacteria or parasites, cancer cells, and foreign cells (transfusions or transplants).

Role of Regulatory T Cells

Dampen the immune response by direct contact or by secreting inhibitory cytokines, important in preventing autoimmune reactions and suppress self-reactive lymphocytes in the periphery.

Immunodeficiency

Congenital or acquired conditions that impair the function or production of immune cells or molecules.

Acquired Immune Deficiency Syndrome (AIDS)

Human immunodeficiency virus (HIV) cripples the immune system by interfering with the activity of helper T cells.

Autoimmune Disease

Results when the immune system loses the ability to distinguish self from foreign.