BMS150 Master Notes PDF

Week 1 Lec 3- B-Cells: Review of Innate Immune system: ​ Macrophages /Neutrophils = phagocytes: break microbes (big things) things into small things and release cytokines ​ Cytokines: are largely involved in inflammation and induce it ○​ Recruit WBC /cell to the correct area, assi...

Week 1 Lec 3- B-Cells: Review of Innate Immune system: ​ Macrophages /Neutrophils = phagocytes: break microbes (big things) things into small things and release cytokines ​ Cytokines: are largely involved in inflammation and induce it ○​ Recruit WBC /cell to the correct area, assist with this migration ​ Complement system: ○​ promote inflammation ​ Ex: C3a, C35= anaphylatoxins --> cause inflammation ​ Anaphylaxis, smooth muscle constriction, vascular permeability ( craws water into the tissue causes swelling ○​ C3b/C5b= opsonin--> opsonization ​ Aid in phagocytosis ○​ MAC- polymerization of C678 etc ○​ Drill hole into microbes causing them to explode T- cells need antigen presentation: ​ 3 professional antigen presenting cells ○​ Dendritic cells: their job is mostly just antigen presentation, thus their specialty ○​ Macrophages: can present antigen and be benefactor of the antigen (helper T cells), with helper T cell help able to do job even better ○​ B cells: can present antigen and be benefactor of the antigen (helper T cells)- with t helper cell help able to do their job even better ​ If need antibody involvement then follicular helper t cells will start to get recruited ​ Cytokines that influences this = IL12 in the reduced appearance of IL2 Fxn of B-Cells: 1.​ Give rise to plasms cells that secrete antibodies capable of binding to an organism, microbe (mostly)or molecule (peanuts, pollen) 2.​ Secreted antibodies have antigen binding sites identical to those of receptor molecules on the b-cell surface --> Whatever it got activated by is only going to create antibodies that have the same specificity ○​ Antibodies= immunoglobulin proteins ​ Once secretes they can protect the host against a wide variety of pathogens B-Cell Development: Review ​ They are type of lymphoid cells ​ T cell and B cells look similar ​ B cells develop 1st from hematopoietic stem cells --> common lymphoid progenitors under the influence of IL7, not until the end of the process is there a differentiation between b and t cells IL-7= the cytokine that influences the cells to eventually break off and become IL-7 ​ Once exposed to B7 then likely to become a B cell and not become a Tcell/NK cell 1)hemopoietic stem cells (Hemocytoblast)--> via IL-7--> 2) lymphoid --> via IL-7--> 3) lymphoblast--> 4)prolymocyte-->5) small lymph ​ 6)Can become either ○​ large granular lymphocyte: Natural killer cells (NK cells) ○​ Small lymphocyte: ​ B lymphocyte--> plasma cell--> B cells are released into circulation as immature naïve b cells = cannot be activated if still naïve ​ T lymphocyte Bone Marrow: 1st step of becoming B cells  1.​ Pre-pro B cells= B cells that develop from lymphoid precursors into these--> can still be influenced to be something else ○​ In early pro- b cells = On the way to 2nd stage the development of IL-7 receptor occurs, this is what commits the development for pro-b cell can be a committed bcell 2.​ Pro- B stage = B cells become irreversibly committed to the B cell lineage once they reach the Pro-B stage --> cannot be influenced to become anything else they are only going to become B cells ○​ This is the stage that immunoglobulin gene recombination begins= generate the diverse array of antibodies required to recognize and combat a vast number of pathogens. It involves the rearrangement of specific gene segments within the immunoglobulin (Ig) genes to create functional antibody molecules. 1.​ Pre-B cell: fully formed b cell receptor made ○​ As the pro-b cell matures to a pre-b cell it be begins to express an immature b cell receptor ​ if this BCR is productive the B cell passes the pr-B cell checkpoint and become a pre-b cell ​ Check point #1= checking if can even bind to antigen/anything ​ If does not then this BCR is unproductive the B cells will undergo apoptosis ​ Before maturing into immature B cells the pre-b cell goes through second checkpoint ​ Check point #2: Checked for self-reactivity --> to avoid autoimmunity ​ (+)--> pre-review: pre-b cells tried to rearrange light chain genes of the BCR and will be checked again for self-reactivity ​ If still (+)--> pre-b cell with undergo apoptosis ​ (-)--> becomes a immature (transitional) Bcell and leaves the bone marrow--> goes to spleen 2.​ Immature B cell/Transitional--> leaves the bone marrow --> spleen ​ As B cells mature their expression of surface B cell markers change--> markers allow for communication of stromal cells in the bone marrow ○​ Cells in any organ that are the support system and thus act as connective tissue ○​ This communication is important bc stromal cells provide the antigens for testing B-Cell Receptor: ​ Membrane bound antibody that associates with a disulfide- liked heterodimer (IG- alpha and IG- beta) ○​ Ig-alpha has a long cytoplasmic tail that’s associated with intracellular signaling molecules B-Cell Development--> Spleen (maturation occurs in spleen) ​ From the bone marrow immature (aka transitional) B cells travel to the spleen --> begins expressing CD21+IgD+IgB= now mature naïve b cell (thus can be activated but has not yet met is match to become activated) --> enters general circulation ○​ CD21: complement co-receptor ○​ IgD + IgM : isomer of the portion of the B cell receptor (BCR) ​ B-Cell Default receptors are IgM for most but during maturation able to have IgD as well B cell Development ---> Lymph Nodes ​ B cells in General circulation --> lymphoid follicle within a lymph node ○​ Beach shaped encapsulated with a reticular network and packed full of lymphocytes, macrophages and dendritic cells ​ 3 main regions: ​ Cortex ​ Paracortex ​ Medulla Cortex: contains lymphocytes → mostly made of B cells -​ Macrophages + follicular dendritic cells arranged into primary follicles → once these follicles get activated they will enlarge into → secondary follicles within germinal centres (where lots of maturation of bcells occur- become more “mighty bcells”) Paracortex: contains mostly T cells (lymphocytes) + dendritic cells -​ Dendritic cells→ express high level of HLA02 molecules + present them to T helper cells for T helper activation and polarization Medulla: sparsely populated with lymphoid linage cells -​ Have fully developed Plasma cells actively secreting antibody molecules that are ready to enter into the circulation and do their job B-Cell Activation: Within Lymph Node if there is an infection -​ Within a lymph node a naive b cell encounters an antigen in 2 ways 1)​ Antigen flows into a lymph node through afferent lymphatics and binds to the b cell receptor 2)​ macrophages /dendritic cells encounter an antigen in the periphery and bring it to a lymph node → where they will “present” the antigen to a B cell and the antigen binds to the b cell receptor → Ag binding to th B cell receptor -​ The antigen bind to the BCR with the help of B cell Co Receptors: → CD21(in spleen): binds antigen bound to complement component of C3d -​ B cell that is immature→ to be mature need the CD21 co receptor in order for B cells to become activated (does not occur until at the spleen)--> once leaves spleen can be activated -​ Is attached to C3d= allows for antigen to bind properly/help mount CD21 onto antigen  → CD19: signal transduction protein (IgM type), they are a guide that will start the continued process -​ Need both CD21 and 19 to bind thus do their jobs in order to → Initiate downstream signaling cascade promoting B cell survival + proliferation *** in terms of cell cycle: before encountering antigen as its mature form thus naive B cell it stays in G0 , after encountering antigen moves into G1 and these 2 proteins (CD21/19) are what make this happen/create this cascade*** Once the antigen binds to the BCR on a Bcell what happened to the antigen? Background info: -​ Helper T cells (follicular T cells): gets activated by IL12 in humans when low IL2 -​ If high IL12 and high IL2 = most likely to become → Th1 bc IL12 is one of the polarizing cytokines→ cytokines that are produced usually by antigen presenting cells bc they are the ones that know what king of infection dealing with -​ Antigens Secreting cytokines and nieve helper t cells need to get influenced and thus going to be sitting in this “soup” of IL12 and in that presents on IL12 that influences Tcells to become either T helper cells (Th1) or follicular (Tfh) -​ If low levels of IL2 → Follicular helper T cells (Th1) Antigen presentation: -​ When have antigen bind to B cell receptor = now exogenous antigen (bc does not start from inside the cell) -​ 1) endocytosis → antigen now inside vesicle to get degraded in the vesicle -​ MHC2 sitting in ER -​ Going through golgi apparatus and being released in its own vesicle -​ Then they will meet and fuse together and antigen put on the surface (clip) -​ Antigen gets mounted on the the HLA2 and go to the surface → Once B cell has presented its antigen it will also increase its expression of co-stimulatory molecules: -​ (on its surface) CD80/86 + binds to CD28 on Th cells for T-cell activation -​ iCOSL + binds to iCOS on Th cells to induce cytokine (IL21 and IL4) productions -​ CD40 + binds to CD40L ( Ligand) on Th (helper T cells) cells to increased antibody production -​ CD40 + CD40L coming from the helper T cell = allows for the B cell to complete its maturation → then the B-cell will present it’s antigen to which type of T-helper cell within the germinal centers of a lymphoid follicle? ​ = Tfh (T follicular helper cell) → Follicular Th cells (Tfh) are the main Th cell that aids full B-cell development in the SLOs → Now that B cell and Tfh cells are locked in an immunologic synapse -​ Co-stimulatory interaction iCOSL and iCOS will stimulate production of cytokines by the Tfh cells -​ Under the influence of IL21, IL4 (by Tfh cell) and CD40-CD40L interaction, the B cell will proliferate and begin to produce antibodies *(**CD8 interacts with HLA1) → B cells need 3 signals for activation 1)​ (bind to a proper antigen)---> Needs to interact with antigen that is not a self antigen (if not = apoptosis) 2)​ Through its HLA2 will interact with a T cell receptor and its CD4 that interacts with MHC2 = co-stimulation happens with iCOS + iCOS ligand→ interaction supercharged the follicular helper T cell to secrete cytokines and upregulate CD40L ​ → cytokines + CD40L = the helpers and allows for full proliferation and differentiation of B cells 3)​ T cell help with CD40L and cytokines IL21 and IL4 Antibody production: -​ After its interaction with Tfh cell/ thus has been activated : -​ Some B cells will differentiate into plasma cells (fully mature) for antibody secretion -​ Early primary response -​ Initially the antibodies will be medium- affinity (not super powered yet)\ -​ Some B cells will move into the germinal centers of lymphoid follicles: -​ Late primary response -​ The influence of particular cytokines secreted by TH1 or TH2 cells will induce antibody class switching -​ Somatic hypermutation (shuffling of genes to increase affinity) will result in production of affinity antibodies (class switching and increasing affinity of antigen binding site) -​ Depending on the what kind of infection the cytokines in the area will influence those B cells to make a certain class of antibodies -​ IgA= neutralization -​ IgG= opsonization, and complement fixation Class switching: in Germinal centres of lymph node -​ During antibody class switching the original antibody (IgM) may be switched to a different class (increased affinity), thus their job can change depending on the infection etc around it but its attraction to their antigens will only grow stronger= not changing specificity, changing their affinity ( to be stronger) -​ IE. IgA, IgE, IgG etc -​ During class switching he specific portion of IgM will be cut off and then re-attached with a different antibody -​ Different cytokines secreted by the T helper cells will induce class switching: if dont have t cells helping then can't have class switching, this they are important for affinity maturation and class switching, it is that CD40 + CD40L rship that is essential for class switching -​ Th1 cells → secrete INF- gamma (helps to get more macrophages involved) = stimulated class switching to → IgG subtype= opsonization (to induce antibody will want more opsonization which aids in phagocytosis) -​ T-Reg Cells–>Secrete→ TGF-beta→ stimulates class switching to→ IgA -​ Th2 cells→ secrete IL4 and IL5→ stimulates class switching to IgE= induce secretion of large amounts of IgM Somatic Hypermutation -​ During the late primary response some B cell move into germinal center of lymph nodes to undergo somatic hypermutation -​ During somatic hypermutation the Variable region of an antibody will mutate at a very high rate (random shuffling making minor changes) -​ then it will be tested for antigen binding → if it binds with higher Affinity it is kept→ going to upregulate its MHC again and interact with the follicular helper T cell and compete its maturation (only 1 scenario where B cell in germinal center go through somatic hypermutation and leaves → bc of increases affinity) → if binds to anything else/ lower affinity = OUT → if it binds with lower Affinity or self the B cell undergo apoptosis (gets selected out) → steps: 1)​ Hypermutation (in dark zone): The B cell starts in the dark zone of a germinal center where it will lose its HLA (that is on is surface) expression and mutate its these cell receptor genes, only small changes made to make its affinity stronger 2)​ Testing/Sampling (light zone): The b cell receptor moves into light zone of the germinal center and sampled follicular dendritic cells for the antigen → self -reactivity/ binding with low affinity to the antigen results in apoptosis **What's it has higher affinity it wants to get activated again it wants that T Cell help to fully differentiate but remember to become a fully forming plasma cell it needs that T Cell help it wants that T Cell help partially because it needs to know like which antibodies am I making right so this T cell is going to release the right cytokines so that this B cell when it becomes a plasma cell it's going to create the right type of antibodies its going to get the IL-21 or IL4 Or or TGF beta or IL gamma. Its going to continue to get informed. And so going from this higher Affinity bcell to a plasma cell the helper T cell can help it -​ Bcells interact with helper T cells twice → once re- stimulated by a tfh cell the B cell will eaither differentiate into a plasma cell or memory B cells Plasma and Memory B cell functions: -​ Following B cell selection in germinal centre for high affinity antibodies, the b cell differentiates into either: → plasma cells: no longer have BCR and secret a large number if antibody molecules → memory b cells: important part of adaptive immunity is that they remember, have higher affinity (vs b cells that develop into plasma cells they have a shorter live bc they do their job and then they move on) → circulate in the periphery -​ Once they re-encounter their specific antigen, they will proliferate and differentiate into plasma cells -​ Continue to express the B cell receptor -​ Much longer lived than naive b cells, live for years so that they can identify when the antigen comes back -​ Differentiation into memory b cells is unclear Antibody Structure: -​ Diff cells have Fc receptor = can bind to stem of antibody General antibody fxn: -​ 6 categories 1)​ Neutralization: Antibody binds to pathogen toxin and inactivating it and preventing binding to cell bc it changed the shape of the receptor so cant bind 2)​ Agglutination: prevents the pathogen from binding to cells and promotes clearance of pathogen, creates clumping of pathogens with antibody thus preventing microbe forbidden to the cells and enhances clearance bc it creates this large messy clump 3)​ Opsonization: antibody binds to FC receptor (found on the phagocyte, not recognizing bacteria itself but the stem of the  antibodies that have opsonized the bacteria) and promotes phagocytosis ex: IgG 4)​ Complement activation: initiates classical pathway of complement pathway and promotes phagocytosis → pathway is induced when an antibody binds to the antigen → job of complement= inflammation, MAC (membrane attack complex), opsonization (promotes phagocytosis) 5)​ Antibody dependent cell mediated cytotoxicity: antibody activates Fc receptors on natural killer cells and inducing apoptosis of infected cell 6)​ Degranulation: antibody activates Fc granulocytes triggering degranulation -​ Antigen have to bind to 2 or more antibodies, other cells also have Fc receptors, binding needs to happen in order to release  Antibody Classes:4 classes each with diff fxns IgM IgG IgA IgE IgD Classes IgG1/2/3/4 Secretes as Pentamer Monomer Dimer Monomer Monomer In small In very small Part of BCR Most common Into tears quantities quantities antibody in Saliva 1st class of serum (blood) Breastmilk antibody Mucus -​ What use secreted during for blood primary immune tests Or in blood as response monomer with similar fxn as Lower affinity for IgG= inducing degranulation of its antigens granulocytes Antibody FXN Activating Opsonization Neutralization Degranulation Most prevalent complement (bind the Fc pathogens in secretions of receptor on Bind to cells the URT Aggulating phagocytes with the Fc pathogens +enhances Agglutination receptor for IgE Binds to (immobilizes phago) pathogens triggering basophils and pathogens for degranulation mast cells phago) IgG1+ IgG3= Degranulation of granulocytes activate (when in (eosinophile, complement monomer state) basophils, mast cells) IgG1 alpha= trigger antibody – needs to have mediated antigen bound cytotoxicity by to both antigen NK cells and FC receptor, if just Complement one of them (classical) bound then not strong enough ADCC signal (2 or more) , which then release ex: histamine for mast calls and thus granulation Secreted early or Early (bc its a Late (in humoral Late Late Late late default, low response) affinity) Signal IL-2 IFN-g TGF-B IL-4 Don't know (cytokines)inducing IL-4 IL-5 class switching IL-5 Study Guide Questions: List the stages of B-cell development in the bone marrow. Outline the two checkpoints in the Bone marrow What is the B-cell called when it leave the Bone marrow Where is the next stage of B-cell development? What is the B-cell called when it leave? Describe the 3 signals needed for B-cell activation Describe the two ways B-cells encounter an antigen What do they do next with the antigen? Which lymphocyte is needed for their activation? How does this cell contribute to activation Following activation: What happens during the early primary response? What is the main class of antibody secreted Describe the affinity of the antibodies secreted? What happens during late primary response? Describe the signals needed for class switching Describe the steps of somatic hypermutation What happens within the light vs dark zones of the lymphoid follicle What are the 6 main functions of antibodies? What are the 5 classes of antibodies? Is the class secreted early or late §What is main function(s) of this antibody class