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Lymphoid System and Immune cells Immunology Unit Dept. of Pathology
35

Lymphoid System and Immune cells Immunology Unit Dept. of Pathology.

Jan 04, 2016

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Page 1: Lymphoid System and Immune cells Immunology Unit Dept. of Pathology.

Lymphoid System and Immune cells

Immunology Unit Dept. of Pathology

Page 2: Lymphoid System and Immune cells Immunology Unit Dept. of Pathology.

Origination of the Immune System Cells

Page 3: Lymphoid System and Immune cells Immunology Unit Dept. of Pathology.
Page 4: Lymphoid System and Immune cells Immunology Unit Dept. of Pathology.

+ CD refers to “cluster of differentiation”+ A molecule with a CD designation has a characteristic cell surface protein.+ These cell surface proteins are often associated with the cell’s function.+ Cells with different functions will express different surface proteins and have unique CD designations.+ Over 300 CD molecules have been described + Abs against these CDs are used as a diagnostic tool and allow us to positively identify different cell types, function, state of activation.

CD (cluster of differentiation) system

Brief summary

Page 5: Lymphoid System and Immune cells Immunology Unit Dept. of Pathology.

Lymphoid Lineage

T Lymphocytes B Lymphocytes Natural Killer Cells

Page 6: Lymphoid System and Immune cells Immunology Unit Dept. of Pathology.

Lymphocytes

~30-40% of WBCs express antigen-specific receptors.express antigen-specific receptors. mediate effector and regulatory influences.mediate effector and regulatory influences. confer long-term immunological memory.confer long-term immunological memory.

T Lymphocytes Mature in thymus Have TCRs (T cell receptors) Recognize Ag on cells only Two subpopulations:

Helper (CD4)Cytotoxic (CD8)

Page 7: Lymphoid System and Immune cells Immunology Unit Dept. of Pathology.

Lymphocytes

B Lymphocytes Mature in bone marrow Have membrane-bound antibodies (Abs)

(~10,000 per cell) Go from “naive” to activated. Plasma cells are Ab secretors

~1-2 week life span

Page 8: Lymphoid System and Immune cells Immunology Unit Dept. of Pathology.

Natural Killer Cells

Detected for anti-tumor activity Lack T and B cell markers Lack Ag receptors Involved with Ab-dependent cell-

mediated cytotoxicity

Page 9: Lymphoid System and Immune cells Immunology Unit Dept. of Pathology.

CD3 on all T cells, NO B cells. CD1 present on developing thymocytes but not on T cells

Among T cells there are two main groups:CD4 “helper T cell” : T helper subgroups >>>>

Th1 * Th2 * (Th3)CD8 cytotoxic T cell

CD19 and 20 are on B cells but not T cells.

CD56 is on NK cells but not other types of lymphocytes.

Key CD Ags to remember

Page 10: Lymphoid System and Immune cells Immunology Unit Dept. of Pathology.

Lymphoid System Primary lymphoid organs

Bone marrow ThymusGeneration & Development

Secondary lymphoid organs Organized

Lymph nodes Spleen

Less organized; MALT: GALT & BALT (Bronchus-Associated Lymphoid Tissue)

Initiation of the adaptive immune response Primary role is generation of specific immune responses. All connected to blood and lymph circulation. All have defined structure (B cell zones, T cell zones...)

Page 11: Lymphoid System and Immune cells Immunology Unit Dept. of Pathology.

Lymphatic System

Network of vessels Collects fluid from tissues Major cell is lymphocyte Unidirectional Often first place where antigens are detected

Blood and lymphatics form an interconnected circulatory system through which immune cells constantly patrol in the absence of Ag

Page 12: Lymphoid System and Immune cells Immunology Unit Dept. of Pathology.
Page 13: Lymphoid System and Immune cells Immunology Unit Dept. of Pathology.

Primary lymphoid organs

Page 14: Lymphoid System and Immune cells Immunology Unit Dept. of Pathology.

Thymus

Structure Gross

Bi-lobed Lies above heart

Microscopic Capsular Lobules with outer cortex and inner medulla

Page 15: Lymphoid System and Immune cells Immunology Unit Dept. of Pathology.
Page 16: Lymphoid System and Immune cells Immunology Unit Dept. of Pathology.

Thymus

Function Takes in immature T cells and puts out

mature (immunocompetent) T cells Increased diversity of T cells T cell selection

Page 17: Lymphoid System and Immune cells Immunology Unit Dept. of Pathology.

T-CELL DEVELOPMENT

Page 18: Lymphoid System and Immune cells Immunology Unit Dept. of Pathology.

Stem cell B cell in Bone marrow

B cell development

Delete self reactive B cells generated by accident.

+5-15% of the circulating lymphoid pool

+Defined by the presence of surface immunoglobulin (BCR).

Page 19: Lymphoid System and Immune cells Immunology Unit Dept. of Pathology.

B cells display surface IgM (monomer)which serves as antigen receptorSurface IgD on some B cells also serves as antigen receptorPre B cells are found in bone marrow and mature B cells are found circulating in bloodstreamAntigen reacts with surface IgM and IgD After antigen binds, B cell is stimulated to proliferate to form a clone of cellsThese selected B cells later differentiate into antibody producing plasma cells that secrete antibody specific to that antigen

B cell development

Page 20: Lymphoid System and Immune cells Immunology Unit Dept. of Pathology.

Secondary lymphoid organs

Page 21: Lymphoid System and Immune cells Immunology Unit Dept. of Pathology.

Lymph Nodes

Structure Gross

Bean-shaped structures Drains major segments of lymphatic system

Page 22: Lymphoid System and Immune cells Immunology Unit Dept. of Pathology.

Lymph Nodes

Structure Microscopic

Major cell types Lymphocytes Macrophages Dendritic cells

Cortex/paracortex/medulla Follicles

Primary Secondary

Page 23: Lymphoid System and Immune cells Immunology Unit Dept. of Pathology.

Peripheral Lymph Node StructurePeripheral Lymph Node Structure

Page 24: Lymphoid System and Immune cells Immunology Unit Dept. of Pathology.

Peripheral Lymph Node StructurePeripheral Lymph Node Structure

Page 25: Lymphoid System and Immune cells Immunology Unit Dept. of Pathology.

Peripheral Lymph Node StructurePeripheral Lymph Node Structure

Page 26: Lymphoid System and Immune cells Immunology Unit Dept. of Pathology.

Lymph Nodes

Function 1st line of response to antigens Secondary follicle (Germinal center) is

site of B cell proliferation, differentiation Specificity is high

Page 27: Lymphoid System and Immune cells Immunology Unit Dept. of Pathology.

Spleen

Structure Gross

Ovoid organ in upper left quadrant of abdomen Microscopic

Compartmentalized Red pulp White pulp Antigen presentation

Major cell types Lymphocytes Macrophages Dendritic cells RBCs

Page 28: Lymphoid System and Immune cells Immunology Unit Dept. of Pathology.

Spleen StructureSpleen Structure

Page 29: Lymphoid System and Immune cells Immunology Unit Dept. of Pathology.

Spleen StructureSpleen Structure

Page 30: Lymphoid System and Immune cells Immunology Unit Dept. of Pathology.

Spleen StructureSpleen Structure

Page 31: Lymphoid System and Immune cells Immunology Unit Dept. of Pathology.

Spleen

Function Filters out older RBCs Responds to Ag in circulatory system Produces activated B cells

Page 32: Lymphoid System and Immune cells Immunology Unit Dept. of Pathology.

Tonsils

Follicular structure Contains lymphocytes, macrophages,

mast cells Germinal centers appear in response

to Ag Protective role in URI (Upper

Respiratory tract Infection)

Page 33: Lymphoid System and Immune cells Immunology Unit Dept. of Pathology.

Appendix

Associated with intestines Responds to Ag Role in GI immune response

Page 34: Lymphoid System and Immune cells Immunology Unit Dept. of Pathology.

MALT

Lymphoid tissues below epithelium Presence of B cells to produce

antibody mainly IgA class.

Page 35: Lymphoid System and Immune cells Immunology Unit Dept. of Pathology.

Myeloid Lineage

Granulocytes Eosinophils Basophils Megakaryocytes Erythrocytes Dendritic cells