ch. 43 part 1 Flashcards
pathogen
any agent that causes disease and infects a wide range of animals (including humans)
ex. of pathogens
- parasites
- protozoa
- fungi
- prokaryotes
- viruses
- prions
2 types of molecular recognition for detection of non-self molecules, particles, and cells
- innate immunity
- adaptive immunity
where is innate immunity found
in all animals and plants
innate immunity in vertebrates
- first response to infection
- foundation adaptive immunity
ex. of innate immunity in insects
- exoskeleton made of chitin forms first barrier to pathogens
- digestive system protected by chitin-based barrier and lysozyme (breaks down bacterial cel walls)
- hemocytes circulate within hemolymph and carry out phagocytosis
- immune system recognizes bacteria/fungi by structures on cell walls
- defense against viruses based on recognition of double-stranded RNA
hemocyte function in insects
- secrete antimicrobial peptides that disrupt the plasma membranes of fungi/bacteria
- carry out phagocytosis in hemolymph
what are the innate defenses of mammals similar to?
those of invertebrates
innate defenses of mammals/invertebrates
barrier defenses, phagocytosis, antimicrobial peptides
innate defenses unique to vertebrates
- natural killer cells
- interferons
- inflammatory response
innate immunity definition
general recognition that something is foreign
barrier defense examples
- skin and mucous membranes of respiratory, urinary, reproductive tracts
- lysozymes that break cell walls in tears, saliva, and mucous of eyes/upper respiratory tract
what does mucus do
trap and allow for removal of microbes
what body fluids are hostile to microbes?
saliva, mucus, tears
what do the low pH of skin and digestive system do
prevent growth of many bacteria
cellular innate defenses (mammals)
- detect, devour, destroy pathogens
how do mammal cells recognize groups of pathogens
TLRs
TLRs - toll-like receptors
recognize fragments of molecules characteristic of a set of pathogens
2 main types of phagocytic cells in mammals
- neutrophils
- macrophages
neutrophils
phagocytic cells that circulates in blood and destroy infected cells
macrophages
phagocytic cells that migrate through the body or reside permanently in organs/tissues
2 additional types of phagocytic cells
- dendritic cells
- eosinophils
dendritic cells
stimulate development of adaptive immunity
- populate tissues that come in contact with the environment
- migrate to lymph nodes after detecting pathogens
eosinophils
discharge destructive enzymes against parasites - multicellular invaders
natural killer cells
tumors, cancers
- circulate through body and detect abnormal cells
- release chemicals leading to cell death, inhibiting spread of virally infected/cancerous cells
what system do many cellular innate defenses involve
lymphatic system
how do peptides and proteins function in innate defense
by attacking pathogens or impeding their reproduction
interferon proteins
innate defense by interfering with viruses and helping activate macrophages
- limit cell-cell spread of viruses
- infected cells release interferons which signal other cells
complement system
causes lysis of invading cells and helps trigger inflammation
how many proteins make up complement system
30
complement protein process
- circulate in an inactive state
- activated by coming in contact with a pathogen
- activation leads to pathogenic cell exploding
inflammatory response
pain and swelling brought about by molecules released upon injury or infection
mast cells
immune cells found in connective tissue
what do mast cells release
histamine
histamine function
triggers blood vessels to dilate and become more permeable
activated complement proteins
- promote further release of histamine
- attract more phagocytic cells
what does enhanced blood flow to a site do
helps deliver antimicrobial peptides
pus
fluid rich in white blood cells, dead pathogens, and cell debris from damaged tissues
what type of inflammation is a fever
systemic - triggered by substances released by macrophages in response to certain pathogens
types of inflammation
local or systemic
septic shock
life-threatening condition caused by an overwhelming inflammatory response
how do some pathogens avoid destruction
- modifying their surface to prevent recognition
- resisting breakdown following phagocytosis
streptococcus pneumoniae
major cause of pneumonia and meningitis in humans
tuberculosis (TB)
disease that kills more than 1 million people a year
what does adaptive immunity rely on
2 types of lymphocytes (white blood cells):
1. T cells
2. B cells
lymphocytes that mature in the thymus
T cells
lymphocytes that mature in the bone marrow
B cells
antigens
substances that can elicit a response from a B or T cell
how to T/B cells bind to antigens
via antigen receptors
- specific to part of one molecule of that pathogen
epitope
small, accessible part of an antigen that binds to an antigen receptor
what is each individual B/T cell specialized to recognize?
epitope on a specific antigen
B cell antigen receptors
Y-shaped molecule w/ 2 identical heavy chains and 2 identical light chains
constant (C) regions or chains on B cells
vary little
variable (V) regions on B cells
different greatly
- provide antigens specificity
how are B cells activated?
when paratope on variable region of antigen receptor binds to the epitope on the antigen
antibody/immunoglobulin
soluble form of the protein secreted by cells
3 functions of complement system
- opsonization
- membrane attack complex
- enhance inflammation
difference between antibodies and antigen receptors
- antibodies: same Y shape but are secreted
- antigen receptors: membrane-bound
composition of T cell receptor
2 different polypeptide chains (a and B)
- tips of chains form variable region, rest is constant region
where do T cells bind
to epitope of antigen fragments displayed/presented on host cell
major histocompatibility complex (MHC) molecules
cell-surface proteins that are bound to antigen fragments
- host proteins that display antigen fragments on cell surface
how are cells infected
- bacterium engulfed by phagocytosis into a dendritic cell and is encased in a phagosome
- lysosomes fuse w/ phagosome and digest bacterium
- immunodominant epitopes are associated with MHC and presented on cell surface
antigen presentation
MHC molecules bind/transport antigen fragments to cell surface
what can a T cell bind to
both the antigen fragments and the MHC molecule
4 characteristics of adaptive immune system
- immense diversity of lymphocytes and receptors
- self-tolerance: doesn’t react against own molecules/cells
- B/T cells proliferate after activation
- immunological memory
how does the immune system assemble millions of different antigen receptors from a small number of parts
by combining variable elemnts
what does an immunoglobulin (Ig) gene encode
light chain of the B cell receptor
what can many different chains be produced from
the same gene by rearrangement of the V, J, and C regions
recombinase enzyme complex
acts randomly to connect different V and J segments in each B cell
rearrangement of chains/segments
- permanent
- passed on to daughter cells when lymphocyte divides
what are rearranged genes transcribed and translated to produce
unique antigen receptors
what are antigen receptors generated by
random rearrangement of DNA
what are lymphocytes tested for
self-reactivity
- if they don’t pass the test = apoptosis (programmed cell death)
are there a few or many lymphocytes with antigen receptors for any particular epitope?
few
- in lymph nodes, antigen is exposed to steady stream of lymphocytes until match is made
what does the binding of a mature lymphocyte to an antigen initiate
events that activate the lymphocytes
how many different B and T cell receptors
- 1 million B
- 20 million T
activated lymphocytes lead to what?
clonal selection - clones made, become effector cells - act immediately against the antigen
plasma cells
effector cells that secrete antibodies
memory cells
effector cells can become memory cells that can give rise to effector cells if same antigen is encountered again
2 types of effector B cells
plasma and memory
2 types of effector T cells
helper and cytotoxic
purpose of antibodies
tag original antigen molecules and mark them for destruction
what is immunological memory responsible for
long-term protections against diseases
primary immune response
first exposure to specific antigen
secondary immune response
memory cells facilitate a faster, more efficient response from a reservoir of T and B memory cells
what can defenses provided by B and T lymphocytes be divided into
- humoral immune response
- cell-mediated immune response
humoral immune response
antibodies help neutralize or eliminate toxins and pathogens in blood and lymph
- B cells, plasma cells
cell-mediated immune response
specialized T cells destroy affected host cells
what does helper T cell activate
- humoral immunity
- cell-mediated immunity
antigen presenting cells
- class I MHC
- class II MHC
antigen-presenting cell
antigen must be displayed on surface
- binds antigen to receptor on helper T cell
class II MHC
provide molecular signature by which antigen-presenting cells are recognized
when happens when antigen receptors on the surface of helper T cells bind to the antigen and the class II MHC molecule
cytokine signals are exchanged between the two cells
- helper T cell is then activate
what happens when helper T cell is activated
proliferates, and forms clone of helper T cells, then activates appropriate B cells
what can antigen-presenting cells be
dendritic cell, macrophage, B cell
what makes a cell an antigen presenting cell
class II MHC
example of cytokines
interleukin-1 and interleukin 2
- allow cells to talk to each other
is innate or adaptive immunity faster
innate
TLR3
binds dsRNA
TLR4
lipopolysaccharides found on many bacterial cells
TLR5
bacterial flagella
CD4 function
protein that checks out MHC 2 molecule to determine if it is actually an antigen-presenting cell
