A&P 21: The Immune System - Innate & Adaptive Body Defenses Flashcards
Immunity
resistance to disease
Innate (nonspecific) defense system
system that responds within minutes to protect the body from all foreign substances
Adaptive (specific) defense system
an “elite fighting force” equipped with high-tech weapons to attack particular foreign substances
Immune system
functional system (rather than an organ system) including a diverse array of molecules plus trillions of immune cells (esp lymphocytes) that inhabit lymphoid tissues and circulate in body fluids
Pathogens
harmful or disease-causing microorganisms
Neutrophils
most abundant type of WBC; become phagocytic on encountering infectious material in the tissues
Macrophages
most voracious phagocytes; “big eaters”; derive from WBC’s called monocytes
Monocytes
WBC’s that become macrophages upon leaving the bloodstream & entering the tissues
Phagosome
vesicle formed as a result of phagocytosis
Phagolysosome
phagosome + lysosome
Opsonins
complement proteins or antibodies that provide “handles” to which phagocyte receptors can bind
Opsonization
process of a pathogen becoming coated with opsonins (“to make tasty”); greatly accelerates phagocytosis of a pathogen
Respiratory burst
promotes killing of pathogens by liberating a deluge of highly destructive free radicals (including superoxide), producing oxidizing chemicals (H2O2 and a substance identical to household bleach), and increasing the phagolysosome’s pH and osmolarity, which activiates other protein-digesting enzymes that ingest the invader
Natural killer (NK) cells
“police” the body in blood and lymph; a unique group of defensive cells that can lyse and kill cancer cells and virus-infected body cells before the adaptive immune system is activated; “pit bulls” of the defense system; part of a small group of large granular lymphocytes
Inflammatory response
triggered whenever body tissues are injured by physical trauma, intense heat, irritating chemicals, or infection by viruses, fungi, or bacteria
Mast cells
key component of the inflammatory response; release the potent inflammatory chemical histamine
Histamine
potent inflammatory chemical released by mast cells
Toll-like receptors (TLRs)
surface membrane receptors; play a central role in triggering immune responses
Kinins, prostaglandins, and complement
inflammatory chemicals
Hyperemia
congestion with blood
Exudate
fluid containing clotting factors and antibodies
Leukocytosis-inducing factors
injured cells release these chemicals
Leukocytosis
increase in white blood cells, characteristic of inflammation
Margination
phenomenon of phagocytes clinging to the inner walls (margins) of the capillaries and postcapillary venules
Diapedesis
process of continued chemical signaling prompting the neutrophils to flatten and squeeze between the endothelial cells of the capillary walls
Chemotactic agents
inflammatory chemicals act as “homing devices”
Chemotaxis
neutrophils and other WBCs migrating up the gradient of chemotactic agents to the site of injury is a positive version of this
Pus
creamy yellow mixture of dead or dying neutrophils, broken-down tissue cells, and living and dead pathogens; may accumulate in a wound
Antimicrobial proteins
enhance our innate defenses by attacking microorganisms directly or by hindering their ability to reproduce; most important of these are interferons and complement proteins
Interferons (IFNs)
some infected cells can secrete these small proteins to help protect cells that have not yet been infected
Complement system (complement)
a group of at least 20 plasma proteins that normally circulate in the blood in an inactive state; include C1-C9, factors B, D, and P, and several regulatory proteins
Classical pathway
1 of 3 pathways by which complement can be activated; involves antibodies (water-soluble protein molecules that the adaptive immune system produces to fight off foreign invaders)
Lectin pathway
1 of 3 pathways by which complement can be activated; involves lectins (water-soluble protein molecules that the innate immune system produces to recognize foreign invaders)
Alternative pathway
1 of 3 pathways by which complement can be activated; triggered when spontaneously activated C3 and other complement factors interact on the surface of microorganisms
Membrane attack complex (MAC)
group of complement proteins, the insertion (into the cell membrane) of which is triggered by C3b binding to the target cell’s surface; forms and stabilizes a hole in the membrane that allows a massive influx of water, lysing the target cell
Fever
abnormally high body temperature; a systemic response to invading microorganisms
Pyrogens
“fire”; chemicals that act on the body’s thermostat (a cluster of neurons in the hypothalamus) - raising the body’s temperature above normal
Adaptive immune system
the body’s built in specific defense system that stalks and eliminates with nearly equal precision almost any type of pathogen that intrudes into the body
Humoral immunity
antibody-mediated immunity; provided by antibodies present in the body’s humors (fluids)
Cellular immunity
cell-mediated immunity; when lymphocytes rather than antibodies defend the body; has cellular targets
Antigens
substances that can mobilize the adaptive defenses and provoke an immune response; ultimate targets of all adaptive immune responses
Nonself
intruders into the body; antigens
Complete antigens
functions in immunocgenicity and reactivity
Immunogenicity
ability to stimulate specific lymphocytes to proliferate
Reactivity
ability to react with the activated lymphocytes and the antibodies released by immunogenic reactions
Hapten
incomplete antigen; troublesome small molecule; unless attached to protein carriers, they have reactivity but not immunogenicity; certain drugs (PCN), chemicals in poison ivy, animal dander, detergents, cosmetics, and a number of common household and industrial products act as these
Antigenic determinants
the parts of the antigen that are immunogenic
Self-antigens
assuming your immune system has been properly “programmed,” these are not foreign or antigenic to you, but are strongly antigenic to other individuals (basis of transfusion reactions and graft rejection)
MHC Proteins
group of glycoproteins among the cell surface proteins that identify a cell as self; each has a deep groove that holds a peptide (either a self-antigen or a foreign antigen)
Major Histocompatibility Complex (MHC)
codes for MHC proteins
B lymphocytes (B cells)
oversee humoral immunity
T lymphocytes (T cells)
non-antibody-producing lymphocytes that constitute the cellular arm of adaptive immunity
Immunocompetence
each lymphocyte must become able to recognized its one specific antigen by binding to it
Self-tolerance
each lymphocyte must be relatively unresponsive to self-antigens so it does not attack the body’s own cells
Primary lymphoid organs
the lymphoid organs where they lymphocytes become immunocompetent (thymus and bone marrow)
Secondary lymphoid organs
all other lymphoid organs besides thymus and bone marrow
Positive selection
1st of 2 tests a developing T lymphocyte must pass; ensures that only T cells that are able to recognize self-MHC proteins survive
Negative selection
2nd test; ensures that T cells do not recognize self-antigens displayed on self-MHC
Naive
immunocompetent B and T cells that have not yet been exposed to antigen; these B & T cells are exported from the primary lymphoid organs to seed/colonize the secondary lymphoid organs (lymph nodes, spleen, etc)
Clonal selection
when an antigen binds to the particular lymphocyte that has a receptor for it, the antigen selects that lymphocyte for further development; if the proper signals are present, the selected lymphocyte will activate to complete its differentiation
Clone
once activated, the lymphocyte rapidly proliferates to form this army of cells all exactly like itself and bearing the same antigen-specific receptors
Effector cells
most members of the clone become these cells that actually do the work of fighting infection
Memory cells
a few members of the clone become these cells that are able to respond quickly after any subsequent encounter with the same antigen
Antigen-presenting cells (APCs)
cells that engulf antigens and then present fragments of them, like signal flags, on their own surfaces where T cells can recognize them
Dendritic cells
cells found at the body’s frontiers (ex. skin) acting as mobile sentinels; very efficient antigen catchers; most effective antigen presenter known
Plasma cells
antibody-secreting effector cells of the humoral response; develop the elaborate internal machinery (RER) needed to secrete antibodies at the rate of 2000 molecules per second; does this 4-5 days then dies
Memory cells
clone cells that do not become plasma cells become these long-lived cells; can mount an almost immediate humoral response if they encounter the same antigen again in the future
Primary immune response
cellular proliferation and differentiation; occurs on 1st exposure to a particular antigen; typically has a lag period of 3-6 days after the antigen encounter
Secondary immune response
if/when someone is reexposed to the same antigen, this faster, more prolonged, more effective response occurs
Immunological memory
memory cells provide this because they are sensitized and already on alert
Active humoral immunity
when B cells encounter antigens and produce antibodies against them, this type of immunity is exhibited
Vaccines
artificially acquired active immunity by receiving dead or attenuated pathogens
Passive humoral immunity
differs from active immunity, both in the antibody source and in the degree of protection; instead of being made by your plasma cells, ready-made antibodies are introduced into your body; conferred naturally on a fetus or infant when the mother’s antibodies cross the placenta or are ingested with the mother’s milk; can be conferred artificially by administering gamma globulin, harvested from plasma
Antibodies
immunoglobulins (Igs); constitute the gamma globulin part of blood proteins
Antibody monomer
4 looping polypeptide chains linked by disulfide bonds combine to form this molecule, with 2 identical halves; whole molecule is T or Y-shaped
Heavy (H) chains
2 of the chains of an antibody monomer are identical to each other and long; have a flexible hinge region at their approximate middles
Light (L) chains
2 of the chains of an antibody monomer are identical to each other and half as long as the other type of chain
Variable (V) region & Constant (C) region
each chain forming an antibody has these 2 regions, 1 on each end
Antigen-binding site
in each arm of the antibody monomer, the V regions of the heavy and light chains combine to form this site shaped to fit a specific antigenic determinant; each antibody monomer has 2 of these sites
Antigen-antibody (immune) complexes
common event in all antibody-antigen interactions is the formation of these complexes
Neutralization
simplest defense mechanism; occurs when antibodies block specific sites on viruses or bacterial exotoxins (toxic chemicals secreted by bacteria); as a result, the virus or exotoxin can’t bind to receptors on tissue cells
Agglutination
clumping caused by cell-bound antigens being cross-linked
Precipitation
soluble molecules (not cells) are cross-linked into large complexes that settle out of solution; much easier for phagoctyes to capture and engulf than are freely moving antigens
IgM
1st immunoglobulin class secreted by plasma cells during the primary response; readily fixes and activates complement; monomer and pentamer forms
IgA
dimer referred to as secretory ___; found in body secretions such as saliva, sweat, intestinal juice, and milk; helps stop pathogens from attaching to epithelial cell surfaces (including mucous membranes and the epidermis)
IgD
monomer found on the B cell surface; functions as a B cell antigen receptor (as does IgM)
IgG
most abundant antibody in plasma (75-85%) of circulating antibodies; main antibody of both secondary and late primary responses; readily fixes and activates complement
IgE
monomer; stem end binds to mast cells or basophils; antigen binding to its receptor end triggers these cells to release histamine and other chemicals that mediate inflammation and an allergic reaction
Monoclonal antibodies
produced by descendants of a single cell; pure antibody preparations specific for a single antigenic determinant
Hybridomas
monoclonal antibodies are made by fusing tumor cells and B lymphocytes; the resulting cell hybrids are called this; like tumor cells, they proliferate indefinitely in culture; like B cells, they produce a single type of antibody
CD4 Cells
type of effector cell that usually becomes helper T cells (TH) that help activate B cells, other T cells, and macrophages, and direct the adaptive immune response
CD8 cells
type of effector cell that usually becomes cytotoxic T cells (TC) that destroy any cells in the body that harbor anything foreign
Class I MHC Proteins
proteins found on the surface of virtually all body cells except red blood cells; each has a groove that holds an antigen - a protein fragment 8 or 9 amino acids long
Endogenous antigens
all antigens displayed on class I MHC proteins are these fragments of proteins synthesized inside the cell
Class II MHC Proteins
second, less widespread type of protein typically found only on the surfaces of cells that present antigens to CD4 cells: dendritic cells, macrophages, and B cells
Exogenous antigens
antigens from outside the cell that have been engulfed by the cell that displays them
T Cell Antigen Receptors (TCRs)
receptors that bind to an antigen-MHC complex on the surface of an APC; has variable and constant regions but consists of 2 rather than 4 polypeptide chains
Co-stimulatory signals
other molecules that appear on the surfaces of APCs in tissues that are damaged or invaded by pathogens
Anergy
state of unresponsiveness to an antigen
Cytokines
the chemical messengers involved in cellular immunity belong to a group of molecules called this; a general term for mediators that influence cell development, differentiation, and responses in the immune system; include interferons and interleukins; include hormone-like or paracrine-like glycoproteins released by a variety of cells
Interleukin-I (IL-1)
released by macrophages; stimulates T cells to liberate interleukin 2 (IL-2) and to synthesize more IL-2 receptors
Interleukin-II (IL-2)
key growth factor; sets up a positive feedback cycle that encourages activated T cells to divide even more rapidly
Helper T (TH) cells
play a central role in adaptive immunity, mobilizing both its humoral and cellular arms
T cell-independent antigens
antigens that activate B cells solely by binding to them; tend to be weak and short-lived
T cell-dependent antigens
most antigens; require T cell help to activate the B cells to which they bind
Cytotoxic T (TC) cells
activated CD8 cells; only T cells that can directly attack and kill other cells
Lethal hit
once cytotoxic T cells recognize their targets, there are 2 major mechanisms - 1 involves perforins and granzymes; the other involves binding to a specific membrane receptor on the target cell that stimulates the target cell to undergo apoptosis
Immune surveillance
NK cells and TC lymphocytes roam the body, adhering to and crawling over the surfaces of other cells, examining them for markers they might recognized, a process called this
Regulatory T (Treg) cells
dampen the immune response; act either by direct contact or by releasing inhibitory cytokines such as IL-10 and TGF-Beta
Autografts
tissue grafts transplanted from one body site to another in the same person
Isografts
grafts donated to a patient by a genetically identical individual (only example = identical twins)
Allografts
grafts transplanted from individuals who are not genetically identical but belong to the same species
Xenografts
grafts taken from another animal species, such as transplanting a baboon heart into a human
Chimeric immune system
way to induce tolerance by temporarily suppressing the recipient’s bone marrow then dousing it with bone marrow from the same donor as the new organ in the hope that this combined immune system will treat the transplanted organ as self
Immunodeficiency
congenital or acquired condition that impairs the production or function of immune cells or certain molecules, such as complement or antibodies
Severe combined immunodeficiency syndromes (SCID)
the most devastating congenital immunodeficiencies are a group of related disorders called this; result from various genetic defects that produce a marked deficit of B and T cells
Acquired immune deficiency syndrome (AIDS)
most devastating of the acquired immunodeficiencies; cripples the immune system by interfering with the activity of helper T cells
Human immunodeficiency virus (HIV)
AIDS is caused by this virus transmitted in body secretions, especially blood, semen, and vaginal secretions; also present in saliva and tears; destroys TH cells, depressing cellular immunity
Autoimmunity
when the body produces antibodies (autoantibodies) and cytotoxic T cells that destroy its own tissues
Autoimmune disease
if a disease state results from autoimmunity, it is called this
Hypersensitivities
result when the immune system damages tissue as it fights off a perceived threat (such as pollen or animal dander) that would otherwise be harmless to the body
Immediate hypersensititivies
acute (type I) hypersensitivities; = allergies
Allergen
antigen that causes an allergic reaction
Anaphylactic shock
systemic response, fairly rare; occurs when the allergen directly enters the blood and circulates rapidly through the body (ex. bee sting, spider bite, injection of a foreign substance such as PCN or other drugs that act as haptens)
Subacute hypersensitivities
caused by antibodies (IgG and IgM); slower onset (1-3 hours after antigen exposure) and the reaction lasts longer (10-15 hours)
Cytotoxic (type II) reactions
reactions that occur when antibodies bind to antigens on specific body cells and stimulate phagocytosis and complement-mediated lysis of the cellular antigens; may occur after a patient has received a transfusion of mismatched blood and complement lyses the foreign RBCs
Immune-complex (type III) hypersensitivities
result when antigens are widely distributed through the body or blood and the huge number of insoluble antigen-antibody complexes formed can’t be cleared from a particular area (may reflect a persistent infection or an autoimmune disease); ex. = Farmer’s lung (induced by inhaling moldy hay) and glomerulonephritis of systemic lupus erythematosus
Delayed (type IV) hypersensitivity reactions
caused by T cells; take longer to appear (1-3 days) than antibody-mediated hypersensitivity reactions; inflammation and tissue damage result from the action of cytokine-activated macrophages and sometimes cytotoxic T cells
Allergic contact dermatitis
most familiar example of delayed hypersensitivity reactions which follow skin contact with poison ivy, some metals, certain cosmetics and deodorant chemicals; these agents act as haptens, and after they diffuse through the skin and attach to self-proteins, the immune system perceives them as foreign
