Flashcards in Immunology I Deck (129):
resistance to disease
What are the two intrinsic systems of the immune system?
innate (nonspecific) and adaptive (specific) defense system
What is included in innate defenses?
skin, mucous membranes, phagocytes, fever, NK cells, antimicrobial proteins, inflammation
What is included in the adaptive defenses?
humoral (b cells) and cellular (t cells) immunity
What is the first line of defense of innate immunity?
skin and mucosa
What is the second line of defense of innate immunity?
antimicrobial proteins, phagocytes
What does the second line of defense of the innate immune system do?
inhibits spread of invaders. inflammation is most important mechanism
What is the third line of defense?
adaptive system. attacks foreign substances. takes longer to react than innate
What are some of the protective chemicals of the surface barriers?
skin acidity, lipids in sebum, dermcidin in sweat, HCl in stomach, lysozyme in saliva/lacrimal fluid, mucus
What are some of the modifications of the respiratory system involved with innate defenses?
mucus-coated hairs in nose, cilia of upper respiratory tract sweep dust/bacteria up
What are the internal defenses of the innate immune system?
phagocytes, NK cells, inflammatory response, antimicrobial proteins (interferon/complement), fever
develop from monocytes to become main phagocytic cell. free macrophages wander thru tissues, fixed macrophages are permanent residents of some organs
What is an example of a free macrophage?
What is an example of a fixed macrophage?
become phagocytic on encountering infectious mat'l in tissues
What is the first step of phagocytosis?
adherence of phagocyte to pathogen
How is the first step of phagocytosis facilitated?
by opsonziation-coating of pathogen by complement or antibodies
What is the second step of phagocytosis?
phagocyte forms pseudopods that engulf the particles forming phagosome
What is the third step of phagocytosis?
lysosome fuses with phagocytic vesicle, forming a phagolysosome
What is the fourth step of phagocytosis?
lysosomal enzymes digest the particles, leaving a residual body
What is the fifth step of phagocytosis?
exocytosis of the vesicle removes indigestible and residual matl
What are the steps for phagocyte mobilization?
leukocytosis, margination, diapedesis, chemotaxis
release of neutrophils from bone marrow in response to leukocytosis-inducing factors from injured cells
neutrophils cling to the walls of capillaries in the inflamed area
inflammatory chemicals (chemotactic agent) promote positive chemotaxis of neutrophils
neutrophils flatten and squeeze out of capillaries
What are the different mechanisms that destroy pathogens by phagocytosis ?
acidification and digestion by lysosomal enzymes, respiratory burst, oxidizing chemicals
release of cell-killing free radicals, activations of additional enzymes
Describe NK cells and what they do?
large granular lymphocytes. target cells that lack self receptors. induce apoptosis in cancer/virus cells. secrete potent chemicals that enhance inflammation
When is the inflammatory response activated?
Triggered whenever body tissues are injured or infected
How does the inflammatory response help the body?
prevents the spread of damaging agents, disposes of cell debris and pathogens, sets the stage for repair
What are the cardinal signs of acute inflammation?
redness, heat, swelling, pain (and sometimes impairment of fxn)
Describe the role of TLRs in inflammation?
macrophages and epithelial cells of boundary tissues have TLRs. Activated TLRs trigger the release of cytokines that promote inflammation
What are the different inflammatory mediators?
histamine, blood proteins, kinins, prostaglandins, leukrotrienes, and complement
What releases kinins, PGs, leukotrienes, and complement?
injured tissue, phagocytes, lymphocytes, basophils, and mast cells
How does inflammation and vasodilation relate?
inflammatory chemicals cause dilation of arterioles and increased permeability of local capillaries--->edema
What does exudate contain?
proteins, clotting factors, antibodies
What is the fxn of exudate?
moves foreign mat'l into lymph vessels, delivers clotting proteins to form a scaffold for repair and to isolate the area
What is the fxn of interferons and complement proteins?
attack microorganisms directly and reduce its ability to reproduce
Explain how interferon works with virus infected cells
viral-infected cells are activated to secrete IFNs. IFNs enter neighboring cells. Neighboring cells produce antiviral proteins that block viral reproduction
What are the fxns of IFNs?
anti-viral, reduce inflammation, activate macrophages and mobilize NK cells
What are genetically engineered IFNs used for?
antiviral agents against hepatitis and genital warts. MS treatment
What does complement do?
major mechanism for destroying foreign substances, amplifies inflammatory response, kills cells by lysis, enhances both nonspecific and specific defenses
Describe the classical pathway of complement activation
antibodies bind to invading organisms. C1 binds to the antigen-antibody complexes (complement fixation)
Describe the alternative pathway of complement activation
triggered when activated C3, B,D, and P interact on the surface of microorganisms
Where do both pathways of complement activation converge?
converge on C3 which cleaves into C3a and C3b
How does complement cause cell lysis?
C3b initiates formation of a membrane attack complex. MAC causes cell lysis by inducing a massive influx of water.
What else does C3b do besides initiate formation of MAC?
What does C3a do?
What are the benefits of moderate fever?
causes the liver and spleen to sequester Fe and Zn and increases BMR speeding up repair
Why are high fevers dangerous?
heat denatures proteins
How is fever initiated?
leukocytes and macrophages exposed to foreign substances secrete pyrogens. pyrogens reset the body's thermostat
substances that can mobilize the adaptive defenses and provoke immune response. large, complex molecules not normally found in body
What are important fxnal properties of complete antigens?
immunogenicity and reactivity
ability to stimulate proliferation of specific lymphocytes and antibodies
ability to react with products of activated lymphocytes and antibodies released
What are some examples of complete antigens?
foreign protein, polysaccharides, lipids, nucleic acids
What are haptens (incomplete antigens)?
small molecules (peptides, nucleotides, hormones), immunogenic when attached to body proteins, cause an immune system to mount a harmful attack
What are some example of haptens?
poison ivy, animal dander, detergents, cosmetics
What are antigenic determinants and what is their fxn?
certain parts of an entire antigen that are immunogenic. antibodies and lymphocytes bind to them
What are self-antigens?
protein molecules on the surface of cells that are antigenic to others in transfusions or grafts. MHC proteins
What are MHC proteins?
coded for by genes of the major histocompatibility complex and are unique to the individual
Class I MHC proteins
found on virtually all body cells
Class II MHC proteins
found on certain cells in the immune response
What do MHC proteins do?
display peptides (usually self-antigens). in infected cells, they display fragments of foreign antigens
What do antigen presenting cells do?
do not respond to specific antigens. play essential auxiliary roles in immunity
Where do B cells mature?
Red bone marrow
Where do T cells mature?
What is immunocompetence?
the ability to recognize and bind to a specific antigen
What is self-tolerance?
unresponsiveness to self antigens
Describe positive selection of T cells
selects T cells capable of binding to self MHC proteins
Describe negative selection of T cells
prompts apoptosis of T cells that bind to self-antigens displayed by self-MHC. ensures self-tolerance
What happens to self-reactive B cells?
are eliminated by apoptosis (clonal deletion), undergo receptor editing, and are inactivated if they escape bone marrow
How is antigen receptor diversity determined?
genes determine which foreign substances the immune system will recognize and resist
What is the fxn of APCs?
engulf antigens, present fragments of antigens to T cells
What are the major types of APCs?
dendritic cells, macrophages, B cells
What do activated T cells do to macrophages?
turn them into insatiable phagocytes and tell them to secrete bactericidal chemicals
Why are dendritic cells unique as APCs?
They are the only ones who have the ability to induce a primary immune response in naive T cells
What critical fxns do dentritic cells perform?
critical in the establishment of memory and maintenance of B cell fxn
What is the antigen challenge and where does it occur?
It's the first encounter btw an antigen and a naive immunocompetent lymphocyte. usually occurs in the spleen or lymph node
What is the fxn of most clone cells?
become plasma cells that secrete specific antibodies
What happens to clone cells that don't become plasma cells?
become memory cells. provide memory and mount immediate response to future exposures of the same antigen
Describe primary immune response.
occurs on the first exposure to a specific antigen. lag period of 3-6 days. peak levels of plasma antibody are reached in 10 days. antibody levels then decline
Describe secondary immune response
occurs on re-exposure to the same antigen. sensitized memory cells respond within hrs. Antibody levels peak in 2-3 days at higher levels. antibodies bind with greater affinity. antibody level can remain high for weeks to months
When does active humoral immunity occur?
when B cells encounter antigens and produce specific antibodies against them
Describe naturally acquired active immunity?
response to a bacterial or viral infection
Describe artificially acquired active immunity?
response to a vaccine of dead or attenuated pathogens
What is the fxn of vaccines?
provide antigenic determinants that are immunogenic and reactive.
Why do vaccines fail to fully establish immunological memory?
because they target only one type of helper T cell
Describe passive humoral immunity
B cells are not challenged by antigens, immunological memory doesn't occur
Describe naturally acquired passive immunity?
antibodies delivered to a fetus via the placenta or to infant thru milk
Describe artificially acquired passive immunity
injection of serum such as gamma globulin. protection is immediate but ends when antibodies degrade
What are immunoglobulins?
the gamma globulin portion of blood
What are antibodies?
proteins secreted by plasma cells that are capable of binding specifically with antigen detected by B cells
Describe the basic antibody structure
T or Y shaped. Two heavy and two light chains. Variable region is where antigen binds
What does the constant region of antibodies determine?
the antibody class (MADGE), the cells and chemicals that the antibody can bind to, how the antibody class fxns in antigen eliminations
first class released during primary response. potente agglutinating agent. fixes and activates complement
found in body secretions. helps prevent attachment of pathogens to epithelial cell surfaces
attached to external surface of B cell. fxn as antigen receptor of B cells
most abundant antibody. Protects against bacteria, viruses, toxins. Fixes complement. Main antibody in secondary and late primary response. Provides passive immunity to fetus
secreted in skin, mucosa of GI and respiratory, tonsils. Binds to mast cells and basophils. When activated causes cells to release histamine that mediate inflammation and allergic rxn. fights parasites
What are the defense mechanisms used by antibodies?
neutralization, agglutination, precipitation, complement fixation
antibodies block specific sites on pathogens. prevent these antigens from binding to tissue cells. antigen-antibody complexes undergo phagocytosis
antibodies bind the same determinant on more than one cell bound antigen. cross-linked antigen-antibody complexes agglutinate
soluble molecules are cross-linked. complexes precipitate and are subject to phagocytosis
What is the main antibody defense against cellular antigens?
complement fixation and activation
What are monoclonal antibodies?
commercially prepared pure antibody. produced by hybridomas (fusion of tumor cell and B cell)
What is the use of monoclonal antibodies?
proliferate indefinately and have the ability to produces a single type of antibody. used in research, clinical testing, and cancer treatment
What are the targets of the humoral response?
bacteria and molecules in extracellular environments
What are the targets of the cell-mediated response?
body cells infected by viruses/bacteria, abnormal or cancerous cells, cells of infused or transplanted foreign tissue
Which MHC proteins do CD4 cells bind to?
Which MHC proteins do CD8 cells bind to?
class I MHC
How do dendritic cells obtain other cell's endogenous antigens?
engulfing dying virus-infected or tumor cells, or by importing antigens thru temporary gap jxns w/infected cells
Describe the role of antigen binding in T cell activation
antigen binding stimulates the T cell, but co-stimulation is required before proliferation can occur
What is co-stimulation?
required T cell binding to other surface receptors on an APC
What triggers proliferation and differentiation of activated T cell?
cytokines (IL-1/2 from APCs or T cells)
What happens to T cells without co-stimulation?
become tolerant to that antigen, are unable to divide, don't secrete cytokines
What happens to T cells that are activated?
enlarge, proliferate, and form clones. differentiate and perform fxns according to their T cell class
What is a crucial co-stimulatory signal for T cell activation?
B7 binding with CD28 receptor on a T cell
What is a B7 protein?
B7 proteins are produced on the surface of dendritic cells and macrophages when innate defenses are mobilized
Why is T cell apoptosis important after immune response has peaked?
activated T cells are a hazard
What is the fxn of cytokines?
mediate cell development, differentiation, and responses in the immune system
What two classes do cytokines include?
interleukins and interferons
Describe the fxn of IL-1
released by macrophages, co-stimulates bound T cells
Describe the fxn of IL-2
key growth factor, acts on cells that release it and other T cells
What is the role of Helper T cells?
once primed by APC antigen, they help activate T and B cells, induce T and B cell proliferation, activate macrophages and recruit other immune cells
What is the role of cytotoxic T cells?
directly attack and kill other cells.
What is the role of NK cells?
recognize lack of class I MHC, antibody coating a target cell, different surface marker on stressed cells.