Chapter 21 – The Immune System (A&P II)

Vocabulary flashcards covering innate and adaptive immune mechanisms, key cells, molecules, clinical conditions, and immunological principles from Chapter 21 lecture notes.

Innate immunity

Nonspecific, immediate defenses including barrier and internal mechanisms present at birth.

Adaptive immunity

Specific, slower immune response that develops memory and targets particular antigens.

First line of defense

Physical and chemical barriers such as skin, mucous membranes, acid mantle, enzymes, mucin, defensins, sebum and sweat.

Second line of defense

Internal innate defenses: phagocytes, NK cells, inflammation, antimicrobial proteins and fever.

Phagocyte

White blood cell that engulfs and digests pathogens; includes neutrophils and macrophages.

Neutrophil

Most abundant phagocyte that becomes phagocytic upon encountering infectious material and dies fighting.

Macrophage

Robust phagocytic cell derived from monocytes; may be free-moving or fixed in tissues.

Opsonization

Coating of pathogens with antibodies or complement to enhance phagocytosis.

Natural killer (NK) cell

Large granular lymphocyte that destroys virus-infected and cancer cells before adaptive immunity is activated.

Inflammation

Localized tissue response producing redness, heat, swelling, pain (and sometimes loss of function).

Histamine

Inflammatory chemical released by mast cells that causes vasodilation and capillary permeability.

Hyperemia

Increased blood flow to an area due to vasodilation during inflammation.

Pus

Creamy mixture of dead neutrophils, tissue cells and microbes that forms at infection sites.

Abscess

Walled-off collection of pus that may require surgical drainage.

Interferon

Antimicrobial protein that protects neighboring cells from viral infection by blocking replication.

Complement proteins

Plasma proteins that, when activated, enhance inflammation, opsonization and cell lysis.

Fever

Systemic rise in body temperature triggered by pyrogens to inhibit microbes and speed repair.

Pyrogen

Substance released by leukocytes/macrophages that resets the hypothalamic thermostat upward.

Antigen

Substance that can provoke an adaptive immune response; usually a large foreign protein.

Immunogenicity

Ability of an antigen to stimulate proliferation of specific lymphocytes.

Reactivity

Ability of an antigen to react with activated lymphocytes or antibodies.

Hapten

Small incomplete antigen that becomes immunogenic when attached to a body protein (e.g., poison ivy).

Antibody (immunoglobulin)

Protein produced by plasma cells that binds specifically to an antigen.

Neutralization

Antibody action that blocks toxic sites of pathogens, preventing their attachment to cells.

Agglutination

Clumping of cell-bound antigens by antibodies for easier clearance.

Precipitation

Cross-linking of soluble antigens by antibodies causing them to fall out of solution.

Complement fixation

Antibody-initiated activation of complement leading to cell lysis.

Monoclonal antibody

Commercially produced antibody specific for one antigenic determinant, used in diagnostics and therapy.

B lymphocyte (B cell)

Lymphocyte responsible for humoral immunity and antibody production.

Plasma cell

Effector B cell that secretes large quantities of antibodies.

Memory B cell

Long-lived cell that enables rapid secondary humoral responses.

T lymphocyte (T cell)

Lymphocyte mediating cellular immunity; includes helper, cytotoxic, regulatory and memory subsets.

Helper T (CD4) cell

T cell that activates B cells, other T cells and macrophages; central coordinator of immunity.

Cytotoxic T (CD8) cell

T cell that directly kills infected or abnormal cells by inducing apoptosis.

Regulatory T cell

T cell that dampens immune responses to prevent autoimmunity.

Memory T cell

Persisting T cell that responds swiftly on re-exposure to its antigen.

Antigen-presenting cell (APC)

Cell that engulfs antigens and displays fragments on MHC proteins for T-cell recognition.

Dendritic cell

Professional APC found in tissues; most potent activator of naïve T cells.

Major histocompatibility complex (MHC)

Self-protein that displays antigen fragments on cell surfaces; key to T-cell recognition.

Clonal selection

Process by which a lymphocyte binds antigen and proliferates into effector and memory clones.

Primary immune response

Initial adaptive response to an antigen; slow with symptomatic period and low antibody titer.

Secondary immune response

Faster, stronger response upon re-exposure due to memory cells; often asymptomatic.

Active immunity

Immunity produced by an individual’s own immune system after antigen exposure.

Passive immunity

Temporary protection provided by receiving preformed antibodies; no memory generated.

Natural active immunity

Antibodies developed after infection by a pathogen.

Artificial active immunity

Immunity gained through vaccination with dead or attenuated pathogens.

Natural passive immunity

Maternal antibodies transferred to fetus via placenta or to infant via breast milk.

Artificial passive immunity

Injection of exogenous antibodies (e.g., antiserum, gamma globulin) for immediate protection.

Cytokine

Chemical messenger (e.g., interleukin, interferon) that influences immune cell activity.

Transplant rejection

Immune attack on transplanted tissue due to mismatched MHC antigens.

Immunosuppression therapy

Medications given post-transplant to prevent rejection, increasing infection risk.

Immunodeficiency

Condition in which immune function is impaired or absent.

SCID (severe combined immunodeficiency)

Genetic disorder with absent B and T cells; treated with bone marrow transplant.

Hodgkin’s disease

Cancer of B cells leading to acquired immunodeficiency.

AIDS (acquired immune deficiency syndrome)

HIV-induced destruction of helper T cells causing severe immunodeficiency.

Autoimmune disease

Condition where the immune system attacks self tissues (e.g., rheumatoid arthritis, type 1 diabetes).

Hypersensitivity

Exaggerated immune response to harmless antigen causing tissue damage.

Immediate hypersensitivity

Antibody-mediated allergic reaction occurring within minutes; involves histamine release.

Anaphylactic shock

Systemic, life-threatening immediate hypersensitivity with widespread vasodilation and airway constriction.

Subacute hypersensitivity

Antibody-mediated reaction with slower onset (hours) causing cytolysis or phagocytosis, e.g., transfusion mismatch.

Delayed hypersensitivity

T-cell–mediated response occurring 1–3 days after antigen exposure; basis of TB skin test.