immunology Flashcards
How do immune cells recognize pathogens
types of recognition
Innate recognition
Adaptive recognition
Innate recognition
Each of a small set of receptors recognizes a molecule absent from animals, but common to a type of pathogen
recognition and response rely on traits common to groups of pathogens
look for specific 3d shapes
innate immune system
preformed barriers, tissues, cells, proteins that share common strategies across animals
first line of defense
barrier defenses and antimicrobial peptides/proteins
cellular innate defenses
lymphatic system
the innate immune system combined strategies can generate the
local inflammatory response
barrier defenses
collection of barriers
- walls
physical barrier like the skin
there are already bacteria and fungi on the skin that will compete with pathogens
lysozymes
ingested bacteria can be destroyed by acidic stomach
defensins
defensive barrier proteins that help when pathogens somehow enter body through openings
tears, mucus, saliva contain the enzyme lysozyme that attacks the cell walls of bacteria
causes lysis –> burst bacteria
defensins
positively charged small peptides that cause lysis
what is an interior physical barrier
mucous membranes
acidic pH
enzymes
epithelial lining of the GI tractd
defensins
cationic proteins
produced by neutrophils
have 3 functions:
1. neutralize toxins by binding to them and blocjing them from perorming their tasks
2. creating pores on bacterial surface with electrostatic attraction-> results in lyse
3. activate other immune cells
lysozyme
enzyme that performs lysis
breaks peptidoglycan layer over bacterial membrane
create pore
water flows in a
barrier defenses- antimicrobial proteins
what antimicrobial proteins exist and what do they do
interferons
immediately made by cells that are infected with viruses
move away from cell that made it
what three things can interfurons do
signals neighboring cells to destroy any RNA that enter them and reduces protein synthesis
signals neighboring cells to undergo apoptosis
activates immune cells which kill infected cells
so what occurs after viral infection
infected cell immediately makes interferons that move away to other cells
virus is able to continue to reproduce for a little
T-cells come and lyse the infected cells
viral load then starts to decrease
complement protein
activation of complement occurs when cell is infective
antibodies from adaptive immune system activate cascade of innate proteins that end up in a pore
lyses
innate system cellular defenses
done by white blood cells, phagocytes and lyphocytes
phagocytes
engulf and digest foreign materials and other specialized coordinate responses
two types called neutrophils and macrophages
all blood cells originate from
stem cells in the bone marrow
progenitor cell
dendritic cells
strategically positioned at points of entry to the body
engulf invaders and initiate defense responses
toll-like receptors
how you recognize non-self
key molecules that alert the immune system to presence of microbial infections
recognize pathogen associated molecular patterns(PAMS) of pathogens
so how do toll-like receptors actually work
a ligand(pathogen associated molecular pattern) fits into binding pocket of TLR and activates it
this causes a change in conformation nd activates subsequent protein transcription and translation of defense proteins –> interferons and defensins
inflammatory response
used in dealing with infection or tissue damage
bacteria make it through barier defense of skin anad is awaited by white blood cells
first resonders are mast cells and they release tumor necrosis factor, prostaglandins, and histamine which trigger inflammation
histamine diffuse away from mast cells and causes capillaries to become leaky allowing plasma and phagocytes to escape the tisssue
after the inflammatory response causes the capillaries to become leaky, what happens
complement proteins and other chemical signals attract phagocytes
neutrophils arrive first, then monocytes
macrophages engulf invaders and are responsible for most of the healing
phagocytes produce cytokines that activate other immune cells
lymphatic system
sewer pipes
branching system of tiny capillaries containing larger vessels
contain lymph that conssits of fluids that accumulate outside the closed circulatory system
in lymph nodes, lymph is filtered and blood cells inspect it for pathogens
contian white blood cells
what two types of DEFENSE mechanisms exist
innate defenses and adaptive defenses
innate defenses
nonspecific defenses
inherited mechanisms that protect thebody from different pathogens
rapid and generalized
adaptive defenses
specific defenses that protect against specific targets
some can evade innate system so second defense
slower and highly specific
specific to one pathogen at a time
what is an antigen
a 3-d foreign shape that is recognized by T cells
antigens are proteins on pathogen surfaces that are composed of epitopes
antibodies uniquely bind to one epitope of antigens
virus can have multiple epitopes
antigen presenting cells
extracellular pathogens
process of linking innate to adaptive immune system
antigen presenting cells include dendrites neutrophils(PMN), macrophages, and B-cells
these APCs engulf pathogens, degrade them, and display the antigen fragments on its own protein receptors, MHCII
specific helper T cells bind to this MHCII complex by the antigen fragment
binding of helper T cell promotes the secretion of cytokines by the antigen-presenting cell(APC) which stimulates proliferation of helper T cell
this proliferation produces clones of activated helper T cells
these clones have receptors of the same antigen and will also secrete other cytokines that activate B cell and cytotoxic T cells (Tc) with the same antigen specificity
major histocompatibility complex proteins
two types
MHCI and MHCII
Class I MHC pathway
APC can be any cell
antigen is intracellular(virus)
APC breaks down proteins in the cell and presents little peptides via MHCI complex, to cytotoxic T cells to prove your cell is not infected
B cell vs cytotoxic T cell difference
B cell is for humoral immunity, the secretion of antibodies by plasma cells
cytotoxic T cells are for cell-mediated immunity which attacks infected cells (MHCI cells)
MHC I
MHC I proteins are present on the surface of every nucleated cell in vertebrates
it randomly samples cytoplasm to ensure no pathogens are present
when cellular proteins are degraded in the proteasome, an MHC I protein may bind a fragment and travel to the plasma membrane to present it
cytotoxic T cells can recognize these antigens and if infected, will kill the cell
MHC II
found mostly on B cells, macrophages, neutrophils, dendritic cells (apc’s)
when an antigen is phagocytosed, it is broken down and presented at the surface by MHCII
this is then recognized by helper T cells
adaptive recognition
uses very specific antigen receptors on mature B or mature T cells
slight differences in amino acid sequence of antigen receptors changes whether or not cells can respond to antigens
two different branches of response in adaptive immunity:
humoral response and cell-mediated response
humoral response
antibodies defend against infection in body fluids
(secretion of antibodies via B-cells)
cell-mediated response
cytotoxic cells defend against infection in body cells
(kill signal via cytotoxic T cells and lysis)
4 defining characteristics of adaptive immunity
- specificity
- diversity
- distinguish self from non-self
- memory
specificity of adaptive immunity
immune system targets small single amino acid variations in epitopes
memory of adaptive immunity
train immune system and recognize pathogens to kill it immediately if it reenters
b-cells
provide diversity via variable regions with cutout that allow epitopes to bind uniquely to site of variable region
each b cell has its own unique variable region
Y shaped with two prongs/antigen binding site
what happens when antigen with specific epitope fits in variable region
this activates that specific B-cell which undergoes mitosis and a clonal expansion
the b-cell will give rise to cells that secrete an antibody
antibodies can recognize specific free antigens as well as antigens on a pathogen’s surface
T cells
one antigen binding site
I shaped
how does humoral regulation work
the two step regulation
produces antibodies
- activation of T-helper cell that recognizes antigen
- activated T helper cell finds B cell that recognizes same antigen
step by step of humoral regulation
antigen is taken up by APC and broken down
antigen piece is bound to MHCII cell and brought to cell surface where a T helper cell recognizes it
cytokines released by APC and t-helper cell, causing t-helper cell to proliferate(clonal expansion)
B-cell that engulfed the same antigen will present it via MHCII to surface where a Th cell receptor will recognize it
cytokines are released that cause B cell to proliferate and b cells can become memory cells or plasma cells
plasma cells will produce antibodies
antibodies are identical to B-cell receptors
antibody molecules are proteins called
immunoglobulins
immunoglobulins
comprised of 2 light chains and heavy chains
variable and constant regions
bivalent
n terminus at binding region
BCR
two major functions of antibodies
agglutination
opsoniation
agglutination
sticking microbes together
blockes escaoe and infection can’t spread
opsonization
specific form of phagocytosis
recepptor mediated
macrophages grab onto antigens with receptors and engulf them
two major classes of T cells
T-helper and cytotoxic T-lymphocytes
cellular response occurs when
virus invades inside your cell
differenec between T-helper and Cytotoxic T-lymphocytes
T-helper: HQ cell that regulates both humoral and cellular immune responses
cytotoxic T lymphocytes: function is to kill other cells via lysois
general process of cellular response
APC will be virally infected and this virus will be broken down and presented via MHC I on cell surface
cytotoxic cell (T cell) recognizes the fragment and proliferates
T cell receptoor recognizes antegenic fragment bound to a MHC I protein of a separate infected cell and T cell releases perforin
perforin creates pores that result in lysis
