Chapter 17 – The Immune System

Vocabulary flashcards covering key terms, cells, molecules, and processes discussed in Chapter 17 – The Immune System.

Innate Immunity

Non-specific defense present at birth; includes external barriers and internal cellular/chemical defenses.

Adaptive Immunity

Acquired, specific defense that develops after exposure to antigens; involves lymphocytes and antibody production.

External Defenses

Physical and chemical barriers (skin, mucous membranes, secretions) that pathogens must cross; part of innate immunity.

Internal Defenses

Cellular/chemical components within blood and lymph (phagocytes, NK cells, complement, interferons); innate immunity.

Antimicrobial Proteins

Innate second-line molecules that kill microbes and attract immune cells.

Complement Proteins

Plasma protein cascade that enhances phagocytosis, inflammation, and cytolysis via membrane attack complex.

Epidermis

Outer skin layer; waterproof barrier that continually sheds, preventing pathogen entry.

Dermis

Inner skin layer containing macrophages that perform phagocytosis.

Gastric Juice

Highly acidic stomach secretion that kills ingested pathogens; first-line defense.

Interferons

Proteins released by virus-infected cells that inhibit viral replication in neighboring cells.

Keratinocytes

Skin cells rich in keratin; shed to remove microbes and provide waterproof barrier.

Langerhans Cells

Skin dendritic cells that alert the immune system to invading microbes.

Lysozyme

Enzyme in tears, saliva, and mucus that digests bacterial cell walls.

Melanocytes

Skin cells producing melanin; protect underlying tissues from UV damage.

Mucous Membranes

Epithelia lining body cavities; mucus traps pathogens for easier destruction.

Natural Killer (NK) Cells

Innate lymphocytes that non-specifically lyse virus-infected and tumor cells.

Phagocytosis

Engulfment and digestion of particles by neutrophils, macrophages, and dendritic cells.

Sebum

Oily skin secretion forming a protective barrier and lowering skin pH.

Transferrin

Iron-binding plasma protein that reduces iron availability for bacterial growth.

Vaginal Secretions

Acidic fluid that inhibits microbial survival in the female reproductive tract.

Neutrophils

First leukocytes to arrive at infection; perform phagocytosis and release NETs.

Monocytes

Blood leukocytes that differentiate into macrophages or dendritic cells at infection sites.

Fixed Macrophages

Tissue-resident phagocytes such as Kupffer cells, microglia, and alveolar macrophages.

Diapedesis (Extravasation)

Process by which leukocytes squeeze through post-capillary venules to reach tissues.

Chemotaxis

Directed movement of immune cells toward higher concentrations of chemical attractants (cytokines/chemokines).

Cardinal Signs of Inflammation

Redness, heat (both from vasodilation), swelling (increased permeability), pain (kinins/pressure).

Antigen

Foreign molecule that stimulates and specifically binds antibody production.

Hapten

Small non-antigenic molecule that becomes antigenic when bound to a larger protein.

Bone Marrow

Primary lymphoid organ where all lymphocytes originate from stem cells.

Thymus

Primary lymphoid organ where T-lymphocytes mature.

Spleen

Secondary lymphoid organ that filters blood and houses immune cells.

Lymph Nodes

Secondary lymphoid organs that filter lymph and facilitate immune responses.

Cell-Mediated Immunity

Defense by T-cells that directly attack infected, cancerous, or transplanted cells.

Humoral Immunity

Antibody-mediated defense executed primarily by B-lymphocytes.

Cytokines

Signaling proteins released by immune cells that regulate immunity and inflammation.

Chemokines

Subset of cytokines that specifically induce chemotaxis of leukocytes.

Opsonization

Coating of pathogens by antibodies/complement to enhance phagocytosis.

Neutrophil Extracellular Traps (NETs)

Webs of DNA and proteins expelled by neutrophils to trap microbes.

Immunoglobulins (Antibodies)

Y-shaped proteins produced by B-cells that bind specific antigens.

IgG

Main serum antibody; crosses placenta; high during secondary immune response.

IgE

Antibody class mediating allergic reactions and defense against parasites.

IgD

Surface antibody on naïve B-cells; function largely unknown.

IgM

First antibody produced; pentamer; includes anti-A and anti-B blood antibodies.

IgA

Primary antibody in external secretions such as tears, saliva, and breast milk.

Constant Region (Fc)

Bottom portion of antibody that is identical within a class and mediates effector functions.

Variable Region (Antigen-Binding Site)

Top portion of antibody that differs between clones and confers antigen specificity.

Neutralization

Antibodies block toxins or prevent viruses from attaching to host cells.

Agglutination

Antibodies bind multiple pathogens, clumping them together for easier clearance.

Precipitation

Cross-linking of soluble antigens into insoluble complexes that enhance phagocytosis.

Complement Activation

Initiation of the complement cascade by antigen-antibody complexes (classical pathway).

Classical Pathway

Complement activation route triggered by antibodies bound to antigens.

Alternative Pathway

Complement activation route triggered directly by pathogen surfaces.

Major Histocompatibility Complex (MHC)

Cell-surface proteins presenting peptide antigens to T-cells for immune recognition.

MHC Class I

Molecules on all nucleated cells (except RBCs) that present to cytotoxic T-cells.

MHC Class II

Molecules on APCs and B-cells that present to helper T-cells.

Cytotoxic T-Cells (CD8⁺)

T-cells that kill infected or abnormal cells recognizing antigen on MHC-I.

Helper T-Cells (CD4⁺)

T-cells that coordinate immune responses by recognizing antigen on MHC-II and secreting cytokines.

Primary Immune Response

First exposure to antigen; slow antibody rise; often accompanied by illness.

Secondary Immune Response

Subsequent exposure; rapid, robust antibody production; usually prevents disease.

Self-Recognition

Ability of T and B cells to recognize the body's own MHC proteins.

Self-Tolerance

Lack of reactivity to self-antigens; loss results in autoimmune disease.