Adaptive Immune Response Flashcards
Humoral immunity
Eliminates extra cellular invaders from blood stream and tissue fluid
Involves B cells (develops from mammals)
Naive B cells become plasma cells which become antibodies.
Antibodies protect host from virus damaging antigens, has a red flag that tags the antigen for rapid elimination.
B cell can’t multiply unless T cell gives it the signal to. Second signal confirms that the antigen is indeed something that needs to be eliminated.
Cell mediated
Deals with intracellular invaders (cancerous cells)
Involves T cells (developed in thymus)
Cytotoxic T cells; responsible for destroying host cells that contain viruses or are corrupt
Helper T cells; are responsible for directing and assisting the various responses of humoral and cell mediated immunity.
The two T cells differ in their cd markers.
T cell receptor doesn’t recognize antigen that is free floating. Antigen has to be presented to it.
Naive lymphocyte
One that hasn’t encountered an antigen
Proliferation of activated lymphocytes
For every single naive lymphocyte that becomes activated, millions of progeny are formed.
Differentiation of activated lymphocyte
Become effector lymphocytes; short lived cells that express traits that help eliminate invaders.
Or become memory lymphocytes; long lived cells that can be activated if the antigen is encountered again.
How are T cells activated?
Dendritic cell presents antigen to T cell
The second signal is that stimulators signals have to be sent. If not, T cells can’t be activated.
Helper T cells
Produce cytokines that activate B cells and macrophages.
Regulatory T cells
Help prevent immune response
Stops immune system from overreacting and responding to harmless substances
Do antigens have to induce an immune response?
No
Two types of antigens
T dependent; t helper cells have to activate B cells
Protein component
T independent; B cells don’t need to be activated by t helper cells
Lps and carbohydrates
Immunogenic
Antigens that elicit an immune response
Proteins produce immune responses more than LPS and nucleic acids
Epitope
Distinct regions of an antigen
Antigenic determinants
Fab region of antibody
Binds antigen
Fc region/
Determines class of molecule
Constant region
Entire fc region and the bottom part of the fab region
Variable region
Top part of the fab region
Neutralization
A toxin or virus that is coated with antibodies cannot attach to cells
Opsonization
Phagocytes have receptors for Fc region of igG molecules so it makes it easier for phagocytes to engulf antibody coated antigens.
C3b also binds to antigen so it’s easier to engulf
Primary response and secondary response
Primary response to an antigen results in the immune system remembering the antigen resulting in the secondary response.
Immobilization and prevention of adherence
Antibodies bind to flagella making the virus immobile . Binding to puli prevents bacteria from attaching to surfaces.
Cross linking
The arms of antibodies can bind to different antigens and make bigger mouthfuls for the phagocyte
Clonal selection
One B cell equals one antibody equals one epitope
Naive lymphocytes are in secondary lymphoid organs and then go to tissues once they encounter their antigen
B cell activation
B cells use Endocytosis to take the antigen and the endosome breaks down the antigen into fragments. These fragments are then delivered to protein structure (MHC class 2). Then the protein structures moves to the surface and presents the fragment to the T cell. If the T cell receptor binds to the fragment then it activates the B cell (by delivering cytokines) this then produces colonel expansion (b cell multiplies) If the T cell doesn't bind, then the B cell becomes anergic and is unresponsive to future antigens of that kind. Become tolerant of it. This prevents self harming.
Characteristics of primary response
Affinity maturation; when B cells multiply, mutations occur on the antigen binding site.
B cells that bind antigen for the longest duration are most likely to proliferate.
Class switching; cytokines induce the B cells to switch that genetic program which causes the plasma cells to secrete other classes of antibodies.
Lymph nodes- igG
Mucosa - igA
After class switching some B cells become memory B cells. They live long after even the antigens are gone. Normal plasma cells die when the antigen is taken care of.
Characteristics of the secondary response
B cells are able to scavenge even low concentrations of antigens because their receptors have been fine tuned through affinity maturation. Has more igA and igG
Rapid production of antibodies
T independent antigen response
Because the epitopes are arranged evenly and repeatedly on the antigen, many B cell receptors bind simultaneously which causes the B cell to be activated (without helper T cell inspection)
These antigens do not produce an immune response in young children (b cell isn’t activated)…causing them to be more susceptible to the pathogens with polysaccharide capsules.
T cell response
J
MHC class 1 and 2
Class 1: all nucleated cells and dendritic cells
Cd marker: CD8
Cell type: cytotoxic T cell
Class 2: B cells, macrophages, dendritic cells (they make the class 2 molecules) Cd market: CD4 Cell type: helper T cell
Cd marker helps identify which T cell is in use (helper/cytotoxic)
Cytotoxic T cell
Delivers cytokines to nearby cells for them to present their antigens so they can locate other infected cells
Destroy cancerous and infected cells
Dendritic cells
Use phagocytosis and pinocytosis to ingest foreign material
When they detect a pathogen they travel to the secondary lymphoid organs where they encounter naive T cells
If it has microbe antigen fragments it produces costimulatory molecules.
If T cells recognize antigen being presented and costimulatory molecules they become activated. If they recognize antigen but don’t see costimulatory molecules they become anergic or become regulatory cells (prevent immune response)
Why do cells apoptosis instead of lyse?
To minimize the number of intracellular microbes that might spill into the surrounding area and infect other cells.
Microbes remain in the cell remnants until they are ingested by macrophages
Helper T cell functions
When presented antigens by the B cell it delivers cytokines to the cell (also drives formation of memory cells)
Can recognize any epitope
When presented antigens by the macrophage it delivers cytokines to the cell.
Gives it more killing power (makes the phagocyte larger, which means more lysosomes and more killing chemicals)
Also joins together macrophages and form granulomas.
Natural killer cells
A group of lymphocytes that lack the antigen specific receptors.
Antibody dependent cells
So they need an antibody in order to induce apoptosis. They have the Fc receptor which binds the red flag portion of antibodies
Delivers perforin and protease to destroy cell
Recognize and destroy stressed host cells
Stressed host cells lack antigen presentation and the NK cell can detect that they are lacking this.
How do you get so many different antibody variation if there are only so many genes?
Each gene has 3 different segments that can join together. V D and J. Called gene rearrangement.
Two immature B cells could start with the same gene arrangement but after it differentiates into a naive B cell some DNA is deleted or added and give rise to different antibody specificities.
Combing the variable regions of the heavy and light chains also makes the antibody more specific.
So 3 times the specificy from the start.
Autoimmunity
When B cells binds and attacks its own host cells.
Why do most T cells undergo apoptosis?
Negative selection: the cell binds to its host cell antigens
Positive selection: the cell doesn’t recognize antigen fragments represent by MHC molecules
