Quiz 4 (lecture 14) Flashcards
What are the 3 defensive strategies used to deal with many hostile environmental factors, not just infections?
avoidance, resistance, and tolerance
- whenever possible all are used (if cannot be used then remaining will be main defenses)
When are avoidance behaviors used?
- to reduce pathogen exposure
- include innate and acquired aversion of markers of high microbial density (smell, taste)
Avoidance is a normal defensive response, but people vary in what?
significantly in expression
- ex. extreme response is germophobia (a common form of OCD)
What do tolerance mechanisms do?
- reduce the negative effects on host fitness of a given level of pathogen burden
- they protect and repair tissues
- we all tolerate chronic viral infections
Do tolerance mechanisms affect pathogens directly?
No, they impose less selection on pathogens than do resistance mechanisms
What is the evolutionary consequence of tolerance mechanisms?
there is less of an “arms race” and little variation among individuals for tolerance genes
T/F Most of us are chronically infected by some virus and tolerate it.
true
If you are infected, then what are your choices and why do you make that choices?
- the choice is to tolerate or resist
- make that decision based on the benefits and cost of resistance (varies among tissues and organs)
typically but not universally, the rule of defense
if possible, avoid; if cannot avoid, resist; if cannot resist, tolerate
What is the aim of resistance mechanisms?
- to eliminate the infection once it is established
What system’s main function is resistance?
- the immune system
– reduce pathogen burden through detection, destruction, and elimination
what is the major cost of resistance?
immunopathology
resistance definition
host use inflammation to reduce infection intensity until the cost of the immune response is larger than the cost of infection in the absence of inflammation
what is the function of the immune system?
to protect the organism against pathogens
what are the problems of the immune system?
- pathogens can re-infect
- pathogens evolve
- pathogens are made from the same stuff that we are
what are solutions of the immune system?
- a memory of past infections
- respond flexibly to pathogens w/ characteristics never seen before
- figure out how to recognize self and not destroy it
Which animals have innate immune systems?
found in all animals
What are the five features of the innate immune system?
- Epithelial barriers (mucosa and skin)
- Phagocytes and their antimicrobial defenses (lysozymes)
- Complement system (coat, smother, and attach to pathogens)
- Anti-viral defenses (NK cells and interferons)
- Anti-parasitic defenses
What does the innate immune system rely on?
pattern recognition receptors to sense microbial infections
What do the pattern recognition receptors sense?
detect conserved structures that are unique to microorganisms
The innate immune system leads to the activation of what? (just in vertebrates)
adaptive immunity
What is the key feature of the adaptive immune system?
The generation of antigen receptors by somatic recombination
What does the adaptive immune systems’ output?
highly diverse repertoire of antigen receptors (antibodies and t cell receptors)
Antigen receptors can detect?
any antigen
(self, microbial non-self, or non-microbial non-self)
What is an antigen?
- any substance that causes an immune system to produce antibodies against it
- is often a small section of a pathogen protein
What is an antibody?
- a protein that binds specifically to a particular substance, its antigen
- antibodies are known collectively as immunoglobulins (Igs)
What are antibodies produced by?
B cells
What are antibodies function?
to identify and neutralize pathogens
what is somatic recombination?
a mechanism of genetic rearrangement that generates a diverse repertoire of antibodies
what do immune cells arise from?
stem cells in bone marrow
Where to t cells and b cells mature?
t cells- thymus
b cells- bone marrow
Where to t and b cells migrate to for processing?
lymph nodes, spleen, tonsils, appendix, and Peyer’s patches
The heavy chain is produced by randomly selecting one gene from which segments?
- 1 of ~40 variable (V) segments
- 1 of 25 diversity (D) segments
- 1 of 6 joining (J) segments
which region is highly diverse across cells (also where the antigen binds)?
variable region
What are the paths that stem cells differentiate in the bone marrow?
- differentiate into B cells in bone marrow
- Migrate to thymus to differentiate into T cells
- Migrate to tissues, differentiate into dendritic cells & macrophages
what happens when immature dendritic cells encounter an antigen?
they internalize it, display its fragments on the cell surface, and migrate to lymph nodes, where they activate naive t cells
when do dendritic cells mature and what is the implication?
mature during migration
lose their ability to engulf pathogens
– will instead deliver one clear signal to T cells
how are cytotoxic t cells activated?
by dendritic cells undergo rapid clonal expansion and then migrate throughout the body in search of cells exhibiting the corresponding antigens
How do t cells kill cells?
- by damaging the cell membrane, which causes the cell to swell and lyse
- through inducing apoptosis, which causes the target cell to shrink and die
what happens when b-cell receptors recognize antigens?
they activate and undergo rapid clonal expansion and clonal selection, gaining increased ability to recognize foreign antigens
What is the first step of clonal selection?
somatic recombination
What is the second step of clonal selection?
B/c receptors created by random recombination, many will bind to self proteins— will be deleted
- end product is a vast diversity of immune receptors
What is the third step of clonal selection?
After clonal selection, immune cells proliferate rapidly through clonal expansion (creates a large # of cells that react w/ the antigen that has been detected)
What is the fourth step of clonal selection?
during clonal expansion of b-cells, affinity maturation occurs
- an improved match to the pathogen (part of clonal expansion)
What is the fifth step of clonal selection?
B cell lineages activated in an immune response set aside some cells to serve as immunological memory
