Lymphoid Cells & Tissues

7/31/2019 Lymphoid Cells & Tissues

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Dr.Kalyan Vikram.V

LYMPHOID CELLS

& TISSUES


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* Lymphoid tissue covers all of the various tissues that areimportant in mounting an immune response.

* A fluid called lymph, (lymph = clear fluid) flows in lymphaticvessels, lymphatic tissue and RBM..* The content oflymphis the same as interstitial fluid, the fluidaround tissue cells,* Lymph eventually drains into venous blood.


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*Primary lymphatic organsarewhere lymphocytesare formed and mature. They providean environment for stem cells to divide and mature into B- andT- cells:

*RBM and*Thymus.

*Both T-cell and B-cells are 'born' in the bone marrow.

*However, whereas B cells also mature in the bone marrow, T-cells have to migrate to the thymus, that is where they mature.


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*Secondary lymphoid tissues

are arranged as a series of filters monitoring the contents ofthe extracellular fluids, i.e. lymph, tissue fluid and blood.

Secondary lymphoid tissues are also where lymphocytesare activated. These include:

*lymph nodes,

*spleen, Tertiary tissues;

*tonsils, CALT

*Peyer's patches

*MALT& GALT.


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*

Lymphocytes:

*Make up 2030% of circulating

leukocytes

*Most are stored, not circulating

Three Classes

*T cells- Thymus-dependent

*B cells- Bone marrow-derived

*NK cells


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T Cells

*Make up 80% of circulating lymphocytes

Three Main Types of T Cells*Cytotoxic T cells

*Helper T cells

*Suppressor T cells

Cytotoxic T Cells*Attack cells infected by viruses

*Produce cell-mediated immunity

Helper T Cells

*Stimulate function of T cells and B cells

Suppressor T Cells

*Inhibit function of T cells and B cells


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B Cells

*Make up 1015% of circulating lymphocytes

*Differentiate (change) into plasma cells or into memory B cells

*Produce and secrete antibodies (immunoglobulin proteins)

*Direct antigen recognition and Antigen presentation

Plasma cells:

*These are the effector cells of the B-cell lineage and are specialised in

secreting immunoglobulins. When activated

*B cells divide, some of its progeny become memory cells and the reminderbecome immunoglobulin-secreting


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T cell B cells. Originate from bone marrow . Originate and mature in

and mature in thymus bone marrow

. They cant function without . They can functions due to

MHC molecules presence of antibody

. They are differentiate into TH . They are not

and Tc

. They have CD8 markers . They have CD4 markers

. They secrete cytokines . They do lysis of the virus-infected cellDifferentiate with exposure to with exposure to hormone

several thymic hormones called cytokine (IL-7)


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Natural Killer (NK) Cells

*Also called Large Granular Lymphocytes (LGLs), these arelarge lymphocytes containing azurophilic granules in the

cytoplasm.

Distribution:

*They account for 10-15% of blood lymphocytes. They are rarein lymph nodes and don't circulate through lymph.


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Functions:

*NK cells are activated by recognition of antibody-coated cells,

virus infected cell, cell infected with intracellular bacteria andcells lacking MHC I proteins.

*antibody-dependent cell cytotoxicity (ADCC).

*NK cells also participate in Graft vs Host reaction in recipientof bone marrow transplants.

*Such cells are called Lymphokine Activated Killer cells (LAK)and have been used clinically to treat tumours. LAK cells have

enhanced cytolytic activity and are effective against wide rangeof tumour cells.


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Dendritic cell-

presents antigens to lymphocytes on its surface.

*These cells are derived from myeloid progenitor in the bonemarrow.

*Their main function is to capture and transport protein antigento the draining lymph node.

*Thy r also present in lymph node, spleen and MALT.

*Mature DCs present Ag to T cells*Most potent APC for nave T cells


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Other cells:

Reticular cell -

also a dendritic cell, which presents antigens.

Mast Cell -derived from the bone marrow,

release histamine, heparin,etc.

Have receptors for IgE antibodies on their surface.

Involved in allergic reactions


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*Thank u

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Lymphoid Cells & Tissues