Immune/Lymphatics

Question 1

Acquired immunity

Answer 1

Develops in response to antigens, more powerful than innate, takes longer to develop, displays specificity and memory.

Question 2

Passive Immunity

Answer 2

Temporary immunity due to donated antibodies (i.e transplacental)

Question 3

Active immunity

Answer 3

Long-lasting/permanent immunity due to self exposure to antigen resulting in memory T cells and B cells specific for antigen

Question 4

Primary lymphoid organ

Answer 4

Precursor cells mature into immunocompetent cells. Each cell is programmed to recognize a specific antigen. Thymus and bone marrow.

Question 5

Secondary Lymph Organ

Answer 5

Trapped atigens stimulate clonal expansions of mature T and B cells. Lymph nodes spleen, tonsils.

Question 6

Lymph follicles

Answer 6

Not enclosed w/i in capsulre (like lymph nodes), occur singly or in aggregates; are sites of B cell localization and proliferation; transient

Question 7

Primary Follicles

Answer 7

Spherical, tightly packed accumulations of virgin B cells and dendritic reticular cells that have not been exposed to antigens

Question 8

Secondary follicles

Answer 8

Derived from primary follicles that have been exposed to nonself (foreign) antigens; not present at birth.

Question 9

Structure of secondary lymph follicle

Answer 9

Corona: darker peripheral region composed of densely packed B lymphocytes
Germinal center: central, lighter stained region composed of B lymphocytes, memory B cells, plasma cells, dendritic reticular cells which function as antigen-presenting cells

Question 10

Diffuse Lymphoid Tissue

Answer 10

Made up of scattered clusters of plasma cells, macrophages, and lymphocytes located in CT stroma and various other sites.

• Subcu-associated lymphoid tissue - papillary layer of dermis
• Lamina propria-associated lymphoid tissue includes: MALT, BALT GALT

Question 11

Aggregated lymphoid tissue

Answer 11

Beneath and in contact with the epithelium - includes various tonsils and Peyer’s patches in the ileum (GALT).

Question 12

Lymphopoiesis

Answer 12

All immune system cells originate in bone marrow. Immature T cells travel to the thymus. B-cells travel to specific regions in lymphoid tissue.

Question 13

B Cells

Answer 13

Maturation of B cells involves the appearance of certain cell surface recetors:
IgM and IgD
MHC class II proteins
Complement receptors
Ig Fc receptors

Question 14

5 Classes of antibodies (immunoglobulins)

Answer 14

IgA, IgD, IgG, Ig M, IgE

Question 15

Antibody structure

Answer 15

2 light and 2 heavy chains
highly variable regions: fab fragment, recognizes antigen
less variable regions: Fc fragment, binds antibody to cells

Question 16

IgA

Answer 16

Found in saliva, milk, GU and respiratory tracts

Question 17

IgD

Answer 17

Found on surface of B cells traveling to lymphoid organs

Question 18

IgG

Answer 18

Major Ig in blood; responsible for most antibody activity

Question 19

IgE

Answer 19

Associated with allergic responses

Question 20

IgM

Answer 20

First antibody class expressed by developing B cells

Question 21

Major Histocompatibility Complex (MHC)

Answer 21

Function: main function of MHC gene products is the presentation of antigenic peptides to T cells

Question 22

MHC I

Answer 22

Expressed on the surface of all cells except trophoblast and red blood cells

Question 23

MHC II

Answer 23

Expressed on the surface of B cells and antigen-presenting cells

Question 24

CD8+ T cells

Answer 24

recognize peptide fragments of foreign proteins bound to MHC class I on the surface of cells. CD8 is a member of the Ig superfamily - it and T cell antigen receptor are required for the binding of MHC class I protein fragments

Question 25

CD4+ T cells

Answer 25

Also recognize peptide fragments of foreign proteins bound to MHC class proteins on surface of APCs (antigen presenting cells) Recognize antigens bound to MHC class II molecules; helper cells - assist CD8+ cell differentiation and B cell differentiation

Question 26

T cells

Answer 26

Pre T cells develop in bone marrow, travel to thymus and complete maturation.

Question 27

CD8+ T cells

Answer 27

``` Cytolytic T cells, bind to an antigen presenting cell, undergo mitosis and release perforins and Fas ligand. Recognize antigens bound o MHC class I molecules, mediators of cellular immunity ```

Question 28

CD16+ T cells

Answer 28

Natural killer (NK) T cells, activated (by tumor cell antigens) T-helper cells release cytokines -- interleukin-2: stimulates proliferation of NK celss Interferon-y: activates NK cells Macrophage activating factor (MAF): activates macrophages Chemotactic factor Tumor necrosis factor (TNF-B): kills tumor cells directly

Question 29

T cell mediated immunity

Answer 29

Macrophage phagocytizes foreign material, foreign proteins are broken down into fragments some of which have antigenic properties (epitopes). Antigens are expressed on surface of macrophage bound to MHC-II. MHC-II/antigen complex is presented to activated helper t-cell, activated t cell undergoes mitosis - some daughter cells become memory cells some secrete interleukins. T cells attract B cells, B cells have access to free antigens and under go mitosis - some daughter cells become plasma cells some become memory cells

Question 30

Complement System

Answer 30

An array of about 20 serum proteins which are synthesized in the liver and found in the blood. Facilitates inflammatory responses and either pathway involves coating the pathogen with complement initiating the cascade.

Question 31

Classic pathway of complement system

Answer 31

Cascade is activated by antibody binding to a pathogen

Question 32

Alternate pathway of complement system

Answer 32

Cascade is directly activated by the pathogen

Question 33

Activation Sequence

Answer 33

C1 (1st complement factor in the cascade) is made up of three subcomponents - C1q, C1r, C1s Immunoglobulins bind to surface of pathogen. C1q binds to Fc region of Ig - activates C1r, activates C1s, initiates complement cascade.

Question 34

Complement cascade results in:

Answer 34

Activation of the membrane attack complex (MAC) on the pathogen leading to perforations and lysis. Production of opsonins, which are coatings that make the antigens more palatable to phagocytes Release of chemotactic agents (chemokines) which attract phogcytes (chemotaxis) to the areas of infection of inflammation

Question 35

Parenchyma

Answer 35

Consists of the cells that typically pack areas of the lymphoid organ: mostly lymphocytes

Question 36

Sroma

Answer 36

Consists mostly of reticular fibers and cells, including undifferentiated cells and fixed free macrophages

Question 37

Lymph Node Hilus

Answer 37

Entry and exit point for vessels - efferent lymphatic vessels as well as arteries and veins exit through the hilus. Afferent lymphatic vessels enter the convex side of the node

Question 38

Lymph node capsule

Answer 38

Dense collagen fibers, some elastic fibers and smooth muscle fibers

Question 39

Lymph node cortex

Answer 39

Outer: contains lymph follicles (nodules) Follicles - contain b cells, follicular dendritic cells and migrating dendritic cells Secondary - mantle, germinal center primary - lack mantle and germinal center Deep - contains T cells, macrophages, high endothelial venules (HEVs): port of entry for circulating differentiated lymphocytes to seed lymph node

Question 40

Lymph node Medulla

Answer 40

Irregular arrangement of loose medullary sinuses and dense medullary cords - sinuses are lined with macrophages, cords consist of blood vessels, lymphoblasts and plasma cells Site of lymphocyte reentry into lymph stream Thymic-dependent areas in subcortical and deeper medullary regions

Question 41

Innate Immunity

Answer 41

Lacks immune specificity and memory; response = inflammation. Neutrophils are the first responders.

Question 42

Capsule of thymus

Answer 42

Contains blood vessels, efferent lymphatics but NO afferent lymphatics (lymph doesn't circulate through thymus). Extends trabelculae (septa) into the parenchyma

Question 43

Trabeculae (septa) of Thymus

Answer 43

Delicate CT, divide the thymus into incomplete lobules

Question 44

Lobules of Thymus

Answer 44

Each lobule is composed of an outer, darker staining cortex and an inner, lighter staining medulla

Question 45

Cortex (dark staining) of thymus:

Answer 45

Stained densely w/ basic dyes such as H&E Cell population: epithelial reticular cells - secrete thymosin. T cells in various stages of differentiation Thymocytes migrate from cortical areas to medullary areas Blood vessels surrounded by continuous epithelial barrier - allows thymus to maintain lymphopoeisis while segregated from antigens

Question 46

Medulla (light staining) of Thymus

Answer 46

Specialized to allow entry channel into blood stream of mature lymphocytes Capillary beds are not sheathed by epithelial cells (more leak) Hassall's corpuscles: Whorls of highly keratinized medullary epithelial cells: produce cytokine thymic stromal lymphopoietin - stimulates thymic dendritic cells needed for the maturation of single positive T cells

Question 47

Development of Thymus

Answer 47

Most developed at puberty - 10-15 grams at birth to 30-50 grams at puberty Involutes during adolescence, no lymph follicles, no afferent lymph vessels, no lymph sinuses

Question 48

Double negative T cells

Answer 48

Lack cell surface molecules typical of mature T cells Enter cortex from blood vessels Proliferate in subscapular area (no CD4 or CD8)

Question 49

Double positive T cells

Answer 49

- Move to outer cortex Confronted w/ epithelial cells w/ cell surface MHC classes I and II for clonal selection Expresses both CD4 and CD8 coreceptors and TCR receptors

Question 50

Single positive T cells

Answer 50

-Move to inner cortex Express TCR receptors and either CD4 or CD8 coreceptors Clonal deletion is completed in the medulla

Question 51

Blood-Thymus Barrier

Answer 51

Located in thymic cortex Prevents antigens in the blood from reaching developing T cells in the thymic cortex Leaky during fetal life to allow for development of immunologic tolerance to self-antigen

Question 52

Morphology of Spleen

Answer 52

No lymph sinuses, no afferent lymph vessels Covered by peritoneum except at hilus Mesothelium-lined CT capsule contains some smooth muscle fibers and send trabeculae into parenchyma Blood vessels enter and leave hilus Divided into red and white pulp

Question 53

Blood filtering function of spleen

Answer 53

``` Only lymphatic organ specialized to filter blood Stores and removes worn out RBCs Recycles iron Converts hemoglobin to bilirubin Blood formation in the fetus ```

Question 54

Immunologic function in Spleen

Answer 54

Screens foreign material in the blood Produces lymphocytes and plasma cells Removal leads to overwhelming bacterial infections in infants, children, and young adults

Question 55

White pulp

Answer 55

Elongated, branched strands always associated w/ arteries. Zones of diffuse lymphoid tissue and germinal centers Site of clonal expansion of antigen-stimulated lymphocytes B cell area contains SECONDARY follicles in which central arteriole is off center T cells are found in the areas surrounding the central artery near the center of the white pulp - forms the periarterial lymphatic sheath (PALS) Reticular fibers are associated w/ fixed macrophages and support splenic pulp

Question 56

Marginal Zone

Answer 56

Forms sinusoidal interface b/w red pulp and white pulp; has an abundance of antigen-presenting cells Lymphocytes first encounter antigens here. Activated T-helper cells activate B cells here

Question 57

Red Pulp

Answer 57

Surrounds white pulp and makes up about 80% of the spleen; functions to filter blood; contains large #s of RBCs and other blood elements Billroth cords form red pulp parenchyma: -Contain various blood cells, plasma cells, and antigen presenting cells -Terminal capillaries open directly into substance of cords (open circulation) -Macrophages destroy worn-out or defective RBCs Venous sinusoid: -Endothelial-lined sinusoids w/ a discontinuous basement membrane -Storage sites for healthy RBCs

Question 58

Vascularization of Spleen

Answer 58

Splenic artery enters hilus, trabecular arteries branch off, central arteries are where adventitia loosens After capillaries form, supplying white pulp, central arteries lose their white pulp investment and enter red pulp to form a penicillus.

Question 59

Penicillus

Answer 59

Composed of pulp arteriole, sheathed arteriole, and terminal capillary Terminal capillary drains into intercellular spaces (open system) or to the venous sinuses (closed system)

Question 60

Veins of spleen

Answer 60

Venous sinuses are lined with reticuloendothelial cells - drain into pulp veins which unite w/ trabecular veins, forming splenic vein which exits at hilus.