Immunocompetent Cells. Differentiation Phases Flashcards Preview

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Flashcards in Immunocompetent Cells. Differentiation Phases Deck (17):
1

Pluripotent hemopoetic (bone marrow) stem cells (HSC)
-> Definition of HSC, Pluripotent and hESC

Hematopoietic stem cell (HSC):
- A stem cell that gives rise to all red and white blood cells and platelets

Pluripotent:
- Having the ability to give rise to all of the various cell types of the body
- e.g. embryonic stem cells
(- cannot make extra-embryonic tissues such as the amnion, chorion, and other components of the placenta)

Human embryonic stem cell (hESC):
- A type of pluripotent stem cell derived from the inner cell mass of the blastocyst

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Hematopoiesis (Def)

- is the production of all of the cellular components of blood and blood plasma (e.g.HSCs)
- occurs within hematopoietic system, wh includes organs/tissues such as bone marrow, liver and spleen
- begins during first weeks of embryonic development

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Process of hematopoiesis

1. HSCs are produced in bone marrow, from which lymphoid progenitor cells( LPC) and myeloid progenitor cells(MPC) arises

2.1 Lymphopoiesis
- immature T- and B-Lymphocytes grow out of LPC-> take place in bone marrow
- they differentiate to pre-T-cell and finally to matured T- and B-Lymphocytes, also nature killer-cells (NK-cells) originate from LPC -> take place in lymphoid organs like Thymus

2.1Myelopoeisis (takes place only in bone marrow)
- From MPC Monocytes, Macrophages, dendritic cells, Granulocytes(basophile, neutrophile, eosinphile GC), Thrombocytes and Erythrocytes arise ->

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Phases in differentiation of immune cells

Ag-independent phase:
- takes place continuously without any antigen in primary immune organs /bone marrow
- ensures a constant level of circulating immune cells

Ag-dependent cells:
- begins with the entry of Ag -> activation of T-and B-Ly in peripheral immune organs

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1. Lymphocytes

- produced in bone marrow
- progenitor Ly differentiate in thymus to T-Ly and in bone marrow to B-Ly
- are monospecific (= wait for their analogous Ag) and recognise a single epitope
- “collect” Ag with their receptors to trigger a protective complementary immune response

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1.1 T-Lymphocytes

- presenters of cellular specific immune response
- Fct.: to recognise the Ags, wh are presented by antigen-presenting cells (APCs) -> able to recognise/destroy intracellular parasites (e.g. viruses)
- each mature T-ly expresses only one type of T-cell- receptor-1 or TCR-2, but never both of them together!
- each mature T-ly expresses only one type of CD-molecule and interacts with only one type of MHC-molecule

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1.1 T-helper cells (CD4+ -receptor)

- produce interferon-γ and interleukins to regulate/ activate other immune cells (“tacticians”) -> enhance the proliferation of other healthy immune cells
- are blind for antigen and need to be activated by APC (“intelligence agent”)
- each T-h cell reacts to one specific antigen
- can recognise only foreign antigens

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1.1 Cytotoxic T-ly cells (CD8+)

- group of T-ly wh recognise tumor cells and virus.infected cells by means of altered cell surfaces, where they bind at receptors presented by MHC-molec.
-> trigger discharge of perforin and granzymes (cytotoxic proteins) which are responsible for the cell dead of tumor or virus-infected cells
- kill only after they get a signal from T-helper cells

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1.2 B-Lymphocytes

- presenters of humeral immune response
- have specific receptors - immunoglobin-D (IgD) and IgM , on its surface for recognising antigens

When B-ly comes in contact wit its antigen:
1. Antigens binds at receptor -> antigen-receptor-complex is concentrated at cell pole and becomes intracellular by endocytosis
2. Ag is reduced in, its fragments are represented by MHC-molecules -> B-ly is pre-activated
3. If pre-activated B-ly comes in contact with complementary T-helper cell (wh recognise the MHC-molec.) the B-ly is activated again and begins to proliferate -> plasma cells arise

- only B-ly, wh produce antibodies against foreign antigens, can be proliferated because Th-cells recognise only foreign antigens

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B-ly antibodies (5 types of Ab)

-IgM: produced at the beginning of immune reaction and stay mainly in blood
- IgG: produced during the process of an infection and represent the biggest portion of antibodies
- IgA: located in mucosa and prevent entering of pathogens
- IgE: responsible for destroying parasites and play important role in allergic reactions
- IgD: located as antigen-receptor on special B-Ly

- antibodies bind specific antigen -> become soluble immune complexes on which complementary factors attach in order that they are endocytosed by cells of innative immunity where they are enzymatically degraded
-> shows that Ab of the specific (acquired) IS are reliant on help of unspecific (innate) IS after their binding to antigens

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1.2 Plasma cells

- arise after 2nd activation of B-ly by T-helper cells (additionally memory-B-cells are proliferated)
- produce and secrete antibodies, wh have same Ag-specificity as the Ig-receptors on parental B-ly
- don’t have Ig- receptors

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2. NK-cells

Function:
- activated NK-cells cause apoptosis on target cell:
1. by direct cytolysis at first contact with virus-infected and tumor cells
2. by antibody-dependent cellular cytotoxicity (ADCC): antibody binds with target cell and come in contact with NK —> triggers secretion of cytotoxic granzymes and perforins wh. lead to apoptosis)
- regulate immune response by secretion of cytokines

Activating receptors:
- recognise foreign antigens on target cells and activate their cytolysis

Inhibiting receptors:
- recognise self MHC-Class1 molecules on target cells and inhibit their destruction

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3. Antigen-presenting cells (APCs)

- activate T-helper cells -> phagocytes bacteria where a part of it goes to surface of phagocyte -> phagocyte presents the antigen to a helper cell and their connect-> T-helper cell is activated

- body’s own cells wh represent fragments of foreign bodies on their cell surface after their come in contact with their antigens
- express MHC-Class2 molecules
- localised in different zones of lymph nodes and present different types of Ags
- “bridge” btw innate and adaptive immunity
- “intelligence agents”

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3. Types APCs (Phagocytes)

3.1 Dendritic cells
- present viral Ags
- strongest T-cell activator

3.2 Macrophages
- present bacterial Ags

3.3 B-Ly
- present bacterial toxins

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Fct of macrophages in innate and adaptive immunity

Adaptive:
- engulf, process and present Ags to T-helper cells (Ags associated with self MHC-Class2 molecules)
- secrete cytokines, wh control proliferation, differentiation and the effector function of Lymphocytes

Innate:
- recognise, destruct and eliminate pathogens without help of immune system
- perform phagocytosis
- secrete cytokines to treat the inflammation (in order to secret pus)

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4. Other cells

4.1 Follicular dendritic cells:
- no APC -> don’t phagocytose
- have dendrites
- catch and keep antigen on their surface

4.2 Mast cells
- intestinal epithelial cells
- element of MALT
- absorb and transport antigens downwards to Ly and APC

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Routes for elimination of antigen

1. Direct cytotoxicity — NK-cells (no need of Ag-presentation) and cytotoxic T-ly ( require Ag-presentation)

2. Indirect cytotoxicity/ Antigen-Dependent-Cellular Cytotoxicity(ADCC) — Macrophages, NK-cells

3. Phagocytosis and Opsonisation

4. Neutralisation of toxins, bacteria and viruses