Trans - Basic Concepts in Immunology Flashcards
overall strategy of immune system
to recognize danger and avoid damage to self
danger - define
potentially harmful agent that may cause damage
damage - define
disruption of normal structure / function
disease - define
clinical manifestation of damage beyond some threshold
danger hypothesis / model theory
core function of the immune system is to perceive danger (rather than recognize nonself)
tolerance - define
unresponsiveness to self or nonself molecules (no immune response)
immunity - define
resistance to harmful effects of disease-causing agents
3 principles in disease-response framework
- host-pathogen interaction
- severity of disease
- host damage
hypersensitivity - define
pathologically exaggerated immune reactions with features of inflammation
hypersensitivity - examples
- allergy - hypersensitivity to allergen
2. autoimmunity - hypersensitivity to self
hygiene hypothesis
insufficient exposure of host to pathogens of natural environment during development leads to increased risk of autoimmunity or allergy
hygiene hypothesis - examples
- C section babies - not exposed to vaginal microorganisms
2. overuse of antibiotics
old friends hypothesis
- old friends - microorganisms very closely associated with the host during evolution (e.g. gut flora)
- old friends train immune system to regulate against hypersensitivity
humoral immunity - define
immunity mediated by soluble substances in body fluids (e.g. protein in plasma, serum)
cell mediated immunity - define
immunity mediated by specialized cells
innate immunity - define
immunity hardwired into genome, usually nonspecific
adapative immunity - define
learned immunity, response to exposure to specific antigens, usually specific
[T/F] innate and adaptive immunity are independent
F
[T/f] innate immunity is the first line of defense
T
antigen - define
substance with potential to be recognized by the immune system
antibody - define
secreted or soluble form of immunoglobulin that can mediate recognition of antigen by the immune system
antibody - structure
- Y-shaped molecule with two antigen-binding arms and 1 trunk
- 4 polypeptide chains - 2 light and 2 heavy linked by a disulfide bond
- antigen binding arm - 1 light chain+part of heavy chain
- Fc region - structure that can be recrystallized
how many chains are in an antibody?
4 polypeptide chains - 2 light, 2 heavy
what bond links the chains of an antibody
disulfide bond
antigen binding arm is composed of:
1 light chain + part of heavy chain
Fc region - define
structure in an antibody that can be recrystalized
variable region of antibodies is located in:
distal part of antigen-binding arm
complementarity determining region - define
variable region of antibodies
IgM - special characteristics
1st to appear during exposure
IgG - special characteristics
majority of circulating antibodies, can cross placental barrier
[T/F] the fact that IgG can cross the placental barrier is always a good thing.
F. If the mother is hypersensitive to the fetus, it may cause a detrimental immune reactions (e.g. erythroblastosis fetalis)
IgA - special characteristics
majority of secreted antibodies in mucosal secretions and colostrum
IgE - special characteristics
responds against parasitic worms
IgD
no biological effector function; major membrane bound antigen in B cells
IgG - % distribution
80
IgM - % distribution
5-10
IgA - % distribution
10-15 mostly in secretions
epitope - define
antigen determinant; part of antigen actually recognized by immune system
paratome - define
part of antibody in direct contact with antigen
opsonization - define
- the process by which antibodies enhance or stimulate phagocytosis
- deposition of opsonin on an antigen, promoting stable adhesive contact with phagocyte
membrane attack complex - define
final result of the complement system, protein-lined transmembrane pore that causes lysis
3 pathways of the complement system
- classical pathway
- alternative pathway
- mannose-binding lectin pathway
complement system - classical pathway
activated by immune complexes of IgM and some subtypes of IgG
complement system - alternative pathway
activated by cell-surface constituents foreign to the host, also activated by classical pathway
complement system - mannose-binding lectin pathway
activated by mannose-bearing foreign substances (e.g. bacteria)
minor source of antibody variation
multiple variant genes in the germline DNA sequence coding for natural antibodies –> pre-immune antibody reportoire
major source of antibody variation
modification of germline DNA sequences to yield multiple variant antibody genes for both heavy and light chains
anatomic barriers in innate immunity
skin, mucous membrane
physiologic barriers in innate immunity
- temperature
- pH
- chemical mediators
responsible for digesting bacterial cell walls
lysozyme
toll-like receptors - define
membrane-bound receptors that recognize commonly encountered pathogen-associated molecular patterns (PAMPs) leading to secretion of cytokines and chemokines
TLR3 - function
recognizes double stranded RNA (e,g, virus)
TLR4 - function
recognizes lipopolysaccharides (e.g. gram negative bacteria cell walls)
cytokines - define
non antibody molecules that regulate immune function as paracrine or autocrine signals
interferon - function
cytokines released from infected cells that induces antiviral state in neighboring cells
chemokines - define
specialized cytokines that attract leukocytes and promote their adhesion to the endothelium
endocytosis - define
internalization of molecules by various cell types through invagination of plasma membrane
phagocytosis - define
endocytosis of particulate matter by specialized cells known as phagocytes
5 cardinal signs of inflammation
- tumor
- rubor
- calor
- dolor
- loss of function
tumor (inflammation) - define
swelling due to increased vascular permeability
rubor - define
redness due to increased blood flow
calor - define
heat due to increased blood flow
dolor - define
pain due to release of pain mediators by inflammatory response cells
clonal selection - define
means to obtain certain lymphocyte populations
negative selection - define
selection before lymphocytes mature - elimination of cells that recognize self, to prevent autoimmunity
positive selection - define
selection after lymphocytes mature - elimination of cells that fail to bind to MHC
cell-mediated immunity involves which two groups of cells?
- lymphocytes
2. antigen-presenting cells
B cells - where do they develop?
bone marrow
B cells - function
upon activation, differentiate into plasma cells or memory B cells
memory B cells - function
long-term immunologic memory (faster 2nd response)
plasma cells - function
secrete antibodies
T cells - where do they mature
thymus
classification of antigens according to T cell activation
- thymus independent
2. thymus dependent
thymus independent antigens - define
antigens that activate B cells without helper T cell
TI-1 - define
polyclonal B cell activators, mitogens that nonselectively induce proliferation of B cells
TI-2 - define
highly repetitious molecules, selectively activate mature B cells bearing antigen specific BCR
TI-2 - mechanism of action
activate mature B cells through extensive cross linking of BCRs by antigen
thymus dependent antigens - define
antigens that require helper T cells to activate BCR
thymus independent antigens - type of immune response
- only IgM produced
- limited immune response
- no immunologic memory
thymus dependent antigens - type of immune response
- class switching (IgM to other classes)
- affinity maturation (stronger affinity of antigen)
- with immunologic memory (generation of memory B cells)
mast cell degranulation - define
acute reaction to antigen due to cross linking of receptor bound IgE on mast cell plasma membranes –> release of histamine
what is the term for systemic mast cell degranulation
anaphylaxis
antibody dependent cell mediated cytotoxicity - define
mediated by nonspecific cells with Fc receptors (e.g. NK cells and monocytes)
antibody dependent enhancement of infection - define
improper or incomplete opsonization may allow pathogens easier access to cells (esp. phagocytic cells)
how do T cells recognize antigens?
through T cell receptor
two types of T cells
- effector (helper T, killer T)
2. regulatory (Treg cells)
helper T cell - function
coordinate immune response to pathogens, activate other cells in immune system
cytotoxic T cell - function
recognize and lyse infected cells carrying antigens bound to class I MHC
helper T cell - receptor expressed
CD4+
cytotoxic T cell - receptor expressed
CD8+
cytotoxic T cell - mechanism of action
lyse infected cells using perforins and granzymes
helper T cell - what does it recognize
antigens bound to MHC II
cytotoxic T cell - what does it recognize
antigens bound to MHC I
Th 1 - function
secrete cytokines that stimulate cell mediated lysis by cytotoxic T cells and macrophages
Th 2 - function
secrete cytokines that stimulate antibody production (IgE)
Th 17 - function
secrete IL-17, involved in recruiting neutrophils and macrophages at interfaces (skin, gut, etc.)
autoimmune regulatory disorders often result from dysfunction in what cell
Th 17
Treg cells - function
express Foxp3 as a transcriptional regulator - suppresses immune response when threat has passed
antigen presenting cells - function
process antigen intracellularly and display epitopes on MHC molecules in cell membrane for recognition by immune cells
major antigen presenting cells
- dendritic cells
- macrophages
- B lymphocytes
major histocompatibility complex - function
- role in recognizing self from nonself
2. hold APC-processed antigens for recognition by immune cells
MHC I - function
enable recognition of antigens by cytotoxic T cells
MHC I - on which cells is it found?
found on most nucleated cells
MHC II - function
enable recognition of antigens by helper T cells
MHC II - on which cells is it found?
found on professional APCs (e.g. macrophages, dendritic cells, B lymphocytes)
what enables cytotoxic T cell activation against viruses and tumors?
cross-presentation
cross presentation - define
presentation of epitopes from exogenous antigens together with MHC I instead of MHC II
cross presentation - on which cells is it found?
only in some APCs, esp. dendritic cells
active immunization - define
- exposure to less potent version of antigen, eliciting endogenous immune response
- produces immunological memory
passive immunization - define
- transfer of preformed immune factors from exogenous source (antibody transfer)
- rapid response but without immunologic memory
which type of immunization is short-term?
passive immunization
blood typing - define
assignment of individuals to various blood groups determined by antigens present in RBC plasma membrane
ABO blood group - basis
presence or absence of oligosaccharide moieties (A & B antigens)
ABO blood group - universal donor
Type O
ABO blood group - universal receiver
Type AB
Rh blood group - basis
presence or absence of RhD/Rh antigen
erythroblastosis fetalis - mechanism
- Rh- mother and Rh+ first baby –> no adverse reaction to the fetus, but the mother will produce anti-RhD antibodies (IgG) that may cross the placental barrier in later pregnancies
- Rh- mother and Rh+ second baby –> anti-RhD antibodies cross the placenta and attack the RBCs of the fetus
tissue typing - define
matching of tissues for predicting compatibility of donor and recipients of tissues and organs
tissue typing - basis
blood group antigens, MHC (human leukocyte antigens)
