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Section 4: Hematopoiesis

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Section 4: HematopoiesisOverview:- What is hematopoiesis?- The formation of red blood cells and white blood cells (leukocytes)- Why are hematopoietic stem cells difficult to study? (HSC)- They are rare (1 in 5x10^4)- Difficult to culture → they do not produce their own unique proteins- HSC are homeostatically maintained→ strike a balance with an immune response, soas to have a response but not cause damage (having the right amount of cells0- However, they can rapidly divide even though there are only few- Example: they can divide in lethally irradiated mice (950 rads)- What does this mean? → A normal mouse has 2x10^8 BM cells; and10^4 cells can reconstitute (.01%)in 950 rad-mice- HSC→ lymphoid or myeloid progenitor cells.Hematopoietic Activity Overtime- Where is it happening?- Yolk sac as you are in the womb- First begins in liver and spleen- Once you are born, and throughout lives,occurs in long bones and cranium, pelvis,etc. → Bone marrow- Class Question: does this activity alwaysoccur in the bone marrow?- No. There are other places where itcan occur.- Example: Someone is HIV+ andabout to acquire immunodeficiency syndrome. You lose your CD4 T cellsand your body continues to make more until the bone marrow depletes.Then, liver and spleen will start to make more T-cells/immune cells.Location of hematopoiesis: Bone Marrow Niche- Niche→ specialized microenvironment- HSC niche is sequestered and contains stromal cells → create a good env forhemato to occur.- Stromal cells→ connective tissues in any organ, fibroblast cells, endothelial cells, etc.- Regulate cell survival, proliferation, differentiation, and trafficking- Drive formation of HSC cell types.Classical Hemato Overview- HSC can become a common myeloid progenitor (CMP) common lymphoid progenitor(CLP)- CLP→ NKCs, B and T cells- CMP→ erythroid CFU (RBC), megakaryocytes (platelets), basophil CFU(basophils), etc.- Cells become more specialized to only make particular cell type- Usually cannot go back, but under certain conditions it can reactivate. Not 100%absolute Question?- CFU→ self renew- Dali→ took a skin cell and generated a sheet. ?- Differentiation→ occurs as a part of creating the right environment. Transcription factorsthen change, which changes proteins and protease made by given cell, and what the cellcan make and do. They then differentiate to an area and become more specialized to acertain role.Hematopoiesis of NK, IL Cells- New: 2011 ?(not on test)- Innate Lymphoid cells:bridge the gap betweeninnate and adaptive immuneresponse.- Adaptive: makeproteins tocommunicate andhelp drive rightresponse- Question: what issomething needed tokeep communicationgoing before we getexpansion of T cellreceptor specific cells, and B specific cells?- This is what separates the innate lymphoid cells from our T lymphocytesis the presence or the absence of the t cell receptor so you dont getspecific activation leading the cytokines, you get activation through othermolecules and receptors guiding this activation ??? lol idk what hessaying here- Create environment conducive to immune response and regulation- Chart walkthrough- CLP→ generate an innate lymphoid cell/NK precursor- NK cells do not have specific T or B cell receptor- NK precursor- Left→ Pre NK, NK cell.- Right→ LTI/ILC (Lymphoid tissue inducer)- LTI→ help remodel and structure lymph node- Keep going right→ generate LTI cells.- Build lymph node where T and B cells, and other cellsreside.- Go left→ ILC precursor (innate lymphoid cell)- Left again→ T-bet TF→ generate ILC 1.- T-bet helps produce IFy cytokine→ helps driveintracellular immunity (gears immune response tointracellular or extracellular)- Question: How to deal with extracellularpathogens→ Antibodies, as well as opsonins andcomplements working on the outside.- Straight down→ Create ILC2- Driven by GATA3 helps to drive interleukin 4 production→helps B cells to produce antibodies- Go right→ RORyt and Arrow hydrocarbon receptor (produces ILC3).- ILC 3→ looks like a Th17 cell w/o t cell receptor → drivesimmune response against extracellular pathogens- Guides AB response and regulates bacterialpopulations- Allows commensals to stay and eliminatepathogens, and pathogenic bacteria to bepathogenic bacteria- TH17→ sometimes a little bit plastic and not as stable intheir phenotype. So when we make RORyt, they can beginto make T-bet again. They can then become XRORyts,looking more like TH1.-- We have NK cells , ILC1s that have T-bet that look like TH1 cells w/ the absenceof T cell receptor, ILC’s that look like TH2 cells with absence of T cell receptor,RORyt and AHR+, ILC3’s which look like TH17 without receptor.Regulation at the Genetic Level- HSC into specific cell types requires expression of different genes at the correct time- Regulated by various transcription factors- Regulate the proteins which in turn regulate what they do- We know about the role of TF because of knockout mice.- Driving a particular phenotype. If you knockout that TF, you can not longer driveprocess.- Ex: IFy is important for particular process→ test it by getting rid of it- Can you still do the thing you thought it was important for? → should beno- But if nothing happens, you put a ton of IFy production in, you canget a lot → overexpress and get an answer.- Not the perfect solution b/c sometimes proteins are expressed fora short period of time. Need to test in a more controlled manner.Hematopoiesis: Essential Transcription Factors- Placeholder slide for importance of TF- Know the starred ones: 3 Transcription Factors- GATA-1→ Guiding: Dependent lineage Erythroid- Bmi-1: Guiding all hematopoietic lineages- b/c its in bone marrow- Ikaros: Guiding lymphoid lineageHematopoietic Homeostasis (HH)- Dynamic equilibrium- Red blood cells→ lifespan of 120 days before phagocytosed by macophagesand get digested into the spleen (4 months)- spleen→ regulates immune response and cleans up RBCs- RBCs can bind glucose. So scientists use to determine how muchglucose is present in blood within a diabetic after 4 months- Test: Take a hemoglobin in Jan, and do it again in June and see ifthe amount of glucose stuck to RBC has gone up or down.- neutrophils→ lifespan of 1 day- Some T lymphocytes→ lifespan of 20-30 years- Memory T cells remember antigens- Humans make 3.7x10^11 white blood cells per day- What controls this HH: Many factors, including cytokines, contribute to maintaining HHMaintaining


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