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Histo Exam III > Immune/Lymphatics > Flashcards

Immune/Lymphatics Flashcards

1
Q

Acquired immunity

A

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

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2
Q

Passive Immunity

A

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

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3
Q

Active immunity

A

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

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4
Q

Primary lymphoid organ

A

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

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5
Q

Secondary Lymph Organ

A

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

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6
Q

Lymph follicles

A

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

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7
Q

Primary Follicles

A

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

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8
Q

Secondary follicles

A

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

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9
Q

Structure of secondary lymph follicle

A

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

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10
Q

Diffuse Lymphoid Tissue

A

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
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11
Q

Aggregated lymphoid tissue

A

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

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12
Q

Lymphopoiesis

A

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

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13
Q

B Cells

A 
Maturation of B cells involves the appearance of certain cell surface recetors:
IgM and IgD
MHC class II proteins
Complement receptors
Ig Fc receptors
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14
Q

5 Classes of antibodies (immunoglobulins)

A

IgA, IgD, IgG, Ig M, IgE

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15
Q

Antibody structure

A

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

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16
Q

IgA

A

Found in saliva, milk, GU and respiratory tracts

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17
Q

IgD

A

Found on surface of B cells traveling to lymphoid organs

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18
Q

IgG

A

Major Ig in blood; responsible for most antibody activity

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19
Q

IgE

A

Associated with allergic responses

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20
Q

IgM

A

First antibody class expressed by developing B cells

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21
Q

Major Histocompatibility Complex (MHC)

A

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

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22
Q

MHC I

A

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

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23
Q

MHC II

A

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

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24
Q

CD8+ T cells

A

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

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25
Q

CD4+ T cells

A

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

26
Q

T cells

A

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

27
Q

CD8+ T cells

A 
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
28
Q

CD16+ T cells

A

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

29
Q

T cell mediated immunity

A

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

30
Q

Complement System

A

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.

31
Q

Classic pathway of complement system

A

Cascade is activated by antibody binding to a pathogen

32
Q

Alternate pathway of complement system

A

Cascade is directly activated by the pathogen

33
Q

Activation Sequence

A

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.

34
Q

Complement cascade results in:

A

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

35
Q

Parenchyma

A

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

36
Q

Sroma

A

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

37
Q

Lymph Node Hilus

A

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

38
Q

Lymph node capsule

A

Dense collagen fibers, some elastic fibers and smooth muscle fibers

39
Q

Lymph node cortex

A

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

40
Q

Lymph node Medulla

A

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

41
Q

Innate Immunity

A

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

42
Q

Capsule of thymus

A

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

43
Q

Trabeculae (septa) of Thymus

A

Delicate CT, divide the thymus into incomplete lobules

44
Q

Lobules of Thymus

A

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

45
Q

Cortex (dark staining) of thymus:

A

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

46
Q

Medulla (light staining) of Thymus

A

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

47
Q

Development of Thymus

A

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

48
Q

Double negative T cells

A

Lack cell surface molecules typical of mature T cells
Enter cortex from blood vessels
Proliferate in subscapular area

(no CD4 or CD8)

49
Q

Double positive T cells

A
  • 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
50
Q

Single positive T cells

A

-Move to inner cortex
Express TCR receptors and either CD4 or CD8 coreceptors

Clonal deletion is completed in the medulla

51
Q

Blood-Thymus Barrier

A

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

52
Q

Morphology of Spleen

A

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

53
Q

Blood filtering function of spleen

A 
Only lymphatic organ specialized to filter blood
Stores and removes worn out RBCs 
Recycles iron 
Converts hemoglobin to bilirubin
Blood formation in the fetus
54
Q

Immunologic function in Spleen

A

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

55
Q

White pulp

A

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

56
Q

Marginal Zone

A

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

57
Q

Red Pulp

A

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

58
Q

Vascularization of Spleen

A

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.

59
Q

Penicillus

A

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

60
Q

Veins of spleen

A

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

Histo Exam III (11 decks)

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