Miller Notes

This was a really bad one to miss. He put things together in a wonderful way that really helped us understand. For those looking for Cook's notes- it'll probably be tomorrow before they are up. It will take a lot of rewriting.

Contact information on handouts.
After today- understand how immune system response to bacteria or viral infection.
2 parts: innate and acquired
Chart of phases of immune response shows all we will talk about today.
3: Innate immune response is critical. number organisms vs time- normal- rapid increase, then plateau, then decline. Without T or B cells, but intact innate, initial infection same, then slow increase due to innate immune response
WITH T or B but without neutrophils, mouse dies fast.
4: variety of microorganisms.
All bacteria have common components.
Rapid response: recognize by preformed nonspecific effector cells- macrophages. Not diverse or specific, but for general features of bacteria.
1st defense is mechanical, chemical, microbiological . Most important mechanical. Lots of cells produce antibacterial peptides. Normal flora compete with potential pathogens. Most potential infections never occur.
3 ways to activate the complement cascade:
classical, lectin, alternative. Alternativen was the 1st in evolution to develop- complement is constantly in circulation. C3b deposition is most important event in cascade- is primary opsonin recognize by macrophage with complement receptors. Makes bacterium more palatable to macrophage and neutrophil. See cascade. Understand role in innate immune response. C3 always cleaved- if deposits on cell surface, then initiates complement activation.
Bacteria destroyed by macrophage- pattern recognition receptors recognize LPS, glycans, etc. When macrophage recognizes through engaging of receptor, uptakes material, activation signal makes macrophage more bacteriocidal, secretes cytokines. Amplifies response. Recruits more phagocytic cells. No long-term protective immunity from this.
Early induced response- macrophage initiates inflammatory response- involves changes in local vascular permeability and vasodilation. Heat- slows pathogen replication and increases activation of immune cells. Swelling- fluid drain to lymph nodes to carry antigen and APCs to initiate acquired immune response. Pain alerts you to problem. Increased number of phagocytes can clear infection.
Receptor-
LPS from gram negative bacteria.
mannose- most bacteria
glycans-bacteria
Engage- signal through TLR for cytokine production. Phagocyte promotes inflammation though cytokines and becomes more bacteriocidal.
TLR- LPS signal is thru TLR-4. Review these.
Macrophage coordinates innate response thru cytokines.
IL-1 activate vascular endothelium, lymphocytes, local tissue destruction- prevents spread of infection. Walls off organisms in inflamed area.
IL-1,6, tnf alpha induce fever
IL-8 attract innate cells, increase access of effector cells by altering adhesion marker profile. Activates integrins. Also activate PMNs.
TNF- see slide. Key cytokine in producing fever. If it produces response systemically- can result in shock.
IL-6- activate lymphocytes, antibody produced,
IL-12 critical for activation NK cells in viral infection. promotes acquisition of response for Th1 development.
Acute phase response- triad of cytokines act on a variety of tissues. See slide. Bone marrow has huge stores of neutrophils. Released on command- kamikazes with a short half life that eat bacteria and die. .million enter oral cavity every day.
hypothalamus- increases body temp. Systemic heat induction.
fat and muscle- protein and energy mobilization
Acute phase response-
acute phase protein- mannose binding lectin and C reactive protein from liver into blood. Complement system.
fibrinogen- part of clotting cascade- helps block off infection site
Creactive protein acts as opsonin or 1st step of complement cascade.
Systemic production cytokines can be deadly-remember shock.
B-1 B cells are CD5+. Produce IgM to bacterial surface. Recognize capsular polysaccharides and cell wall components. Crosslink receptors- get IgM- opsonin. No IgM receptors on phagocytes, but initiate complement cascade. Deposit C3b, then the bacteria get taken up. No memory. No clonal expansion and no memory.
Controlling viral infection:
Viruses induce cells to produce type 1 interferon, Alpha and beta. Activate NK cells, and make adj uninfected cells less susceptible to infection. Cells upregulate MHC class I expression on surface.
Time vs virus titer- after few days up, then down due to acquired response. Rate of viral replication low at first- held down by NK cells. IL-12 is from dendritic cells infected with virus.
NK cells kill cells that don’t express MHC class 1. Most cells express it. Neural cells do not. Why NK cells dont attack neurons-he does not know. Viruses take over protein production machinery of cell and turn off host cell protein production to provide viral protein. After few hours, MHC class 1 molecules are not replaced. Once the cell has lost MHC class 1, it becomes a target for NK killing.
NK cells perforin and granzymes(initiate apoptotic pathway)- release granules to kill in antibody cell-mediated killing (acquired response) or cells without MHC class 1- have activation and inhibition receptors. MHC rec by inh receptor. Inh killng cell.
Other adhesion molecules initiate reaction- sampling of surface occurs.No MHC-dump granules and kill cell. If you experimentally Bind MHC1 with an antibody to mask its presence- NK cell can kill healthy cell.
Without MHC, how do CD8 cells recognize sick cells? They don’t. They recognize cells early in infection. MHC class 1 will be full of viral protein at the time. Late- class 1 gone and NK cells can kill. T cells recognize early in replication cycle, and destroy. NK cells can’t completely control a viral infection because they kill late in replication cycle and viruses are released. T cells better limit virus replication than NK cells.
Acquired immune response slides
1- summary
2- typical course infection. Immune system is designed to respond to intermediate amounts of antigen, above a certain threshold.
After 4-5 days- transport of antigen to secondary lymphoid tissue promotes recognition, clonal expansion and differentiation- removal infectious agent.
Different mechanisms as we go.
Immature dendritic cells are Langerhans cells- can’t present antigen because they do not express costimulatory B-7 molecule. Why does presentation have to happen in lymphatics? APC contacts large number T cells in lymph node- better probability of running into cell with right specificity. Take up antigen in periphery, mugrate to T cell zones of lymphoid tissue, Constitutively produce B-7, progress.
REALLY understand MHC class I and II. 2 pathways allow recognition of intracellular pathogen or extracellular pathogens.
Class II- extracellular pathogen. Most bacteria. Bacterium is phagocytosed, goes to endocytic vesicle, to lysosome, dismantled, class II-peptide complex takes peptide anigen to surface, present to naive T cells. Some class II antigen may get into class I or antigen from class I pathway may get into class II, but mostly works. CD4 cells recognize these.
Class 1- intracellular bacteria, or all viruses intracellular. Protein production in cytoplasm. Fed into proteasome. Presented to CD8 T cells.
T cell activation- 2 signals. 1st is TcR on naive T- recognize cognate peptide Only activate with B7-CD28 signal.B7 is costimulatory molecule on APC, CD28 on T cell. Only get 1st signal- anergic and die. No B-7 – means it is response to self antigen. b-7 upregulated in infection. This is peripheral tolerance (most tolerance is thymic).
Once T cells fully differentiate, armed and proliferate. Most new cells become effector T cells. No further costimulation is necessary. Recognize peptide- perform function. Express different adhesion molecules.
CD8 cell does NOT activate in secondary lymphoid tissue due to different adhesion molecules.
Il-2 is autocrine growth factor. They also produce high affinity IL-2 growth factor so the cell stimulates itself.
Cytotoxic T cells only kill recognized cell. Can kill many cells due to regeneration of lytic granules. CTLs recognize MHC class 1 molecules.
Adhesion molecules initiate reaction.
3 types effector T cells to know:
CD8 are CTL. killer CD8s.
CD4:
differentiate into Th1 ot Th2. depends on cytokines.
Th1- most of CD4 cells. These direct response to intracellular pathogens. Activate macrophages. MHCII mostly on APC (outside thymus). Th1 recognize class II- activate more bacterocide, more inflammatory cytokines. Many initracellular bacteria live inside macrophage, which can kill them if it is activated.
Th2- extracellular-promote response to extracellular pathogens. Activate B cells.
Different T helper cells:
All CD4+ naive cells are Th0- not precommitted.
Activate, proliferate, then differentiate to Th1 or Th2 depending on cytokine signals. If effector T differentiate toward Th1, activate macrophage, B cells for opsonization of antigen. Th2- b cells for neutralizing antigen. Th1 and th2 can supply different cytokines for 2nd signal to B cells. Th1 activate class switching for intracellular pathogens. Th2 for extracellular.
What drives differentiation Th0 cells?
cytokine environment. is primary driver. CD4- IL-12+IFNgamma-Th1
CD4- IL-4 (from NK 1.1)- Th2 phenotype. Produces IL-4 and 5- promote class switch to antibody for extracellular pathogens.
Antigen also influences pathway. Antigen low affinity or lowconcentration Th2
High affinity or high concentration- Th1. Get more concentration from intracellular infection.
After Th cell is produced- Th2 inhibits Th1,and vice versa. response highly polarized.
What do Th1 do? see slide.p7.
diapedesis- aloow macrophages into infection site. Chemotactic factor draws macrophages in.
B cell activation and differentiation:
1. Engage membrane bound antibody molecule- endocytose complex, degrade, load class II molecule, to surface, present to naive T cells.T cell signals back- B cell becomes plasma cell. Not-B cell anergic.
B cell migrate into T cell zone, interacts with effector T cells, recognizes peptide MHCII complex, T helper activate B cell, proliferates, pairs of B cell-T cell move into follicle and replicate to form germinal center. All cells with same antigen specificity- affinity maturation happens here. High rate mutation in complementarity determining regions of heavy and light chain produce antibodies with different affinity for antigen than initial B cell receptor had.some lower, some higher. Higher affinity is selected to continue development. Follicular dendritic cells are different. Supply survival signals and hold antigen for long period of time. Lower affinity B cells die.Affinity of group increases significantly over time. Surrounded by helper Ts proliferating- make cytokines to promote class switching to different types antibody.
What happens in germinal center- 2 important things:
affinity maturation
isotype swtching
1st isotype always IgM- always constant, and affinity does not increase over time. Over time- switch to IgG eventually, and affinity increases after 3rd exposure to vaccine. concentration antibody also increases over time.
Should know Antibody functions w 3 +++. IgA- mucosal. IgE-mast cell sensitization.
Mechanisms antibodies to clear infection:
opsonization- Fc receptors bind antibody only when it is bound to antigen. complement is further opsonin.
Other key- neutralize antigen. Bacterial toxin usually binds to receptor on cell to produce damage. Antibody binds to the toxin to prevent toxin access to cell and render it palatable for macrophage destruction.
Another role antibody- NK-Mediated ADCC
NK have Fc receptors.
Mast cells- deal with parasites, extracellular, like GI pathogens. Granules promote powerful inflammatory response. Sytemic- explosive diarrhea, vomiting, can result in anaphylactic shock. Have no antigen specific receptors- have IgE receptors. Serum IgE low- taken up through FcE reseptors on mast cells. Used as antigen receptors with different specificities- crosslink with antigen- mast cell degranulates. Hives- local degranulation.
Know protective immune response is mediated by T cell and/or B cell responses. Innate not amplified or changed.
B cell differentiation results in plasma cell or memory B cell. May be some T cell memory, or not . Not well understood.
Initiate response- control infection. Infection few wks later- handled quickly.
Be able to understand what happens if infection with particular organism- virus or bacterium.