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Lymphoid System Flashcards

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1
Q

Antigens (Ag)

A

. Molecules recognized by cells of immune system

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2
Q

Cells of immune system

A

. Lymphocytes
. Macrophages
. Dendritic cells
. Granulocytes

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3
Q

Innate immunity

A

. Nonspecific, quickly utilized
. No previous exposure needed
. Macrophages, dendritic, granulocytes involved
. Have physical and chemical barriers of skin and mucous membranes to contribute

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4
Q

Adaptive immunity

A

. Specific response mediate by lymphocytes
. Need previous exposure of antigen
. Only small number lymphocytes will recognize particular antigen
. Slower response
. Generates immunologic memory
. Uses cellular and humoral immune responses

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5
Q

What occurs when lymphocyte recognizes particular antigen?

A

. Activates and divides

. Undergoes clonal expansion where millions of identical effector cells are made

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6
Q

Cellular immune response

A

. Mediated by T lymphocytes

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7
Q

Humoral immune response

A

. Mediated by plasma cell-produced antibodies

. Bind to antigens to mark for destruction

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8
Q

Antigen presenting cells

A

. Antigens processed before recognition
. Found in skin, lymph nodes, spleen, thymus, mucosal epithelia
. Dendritic, langerhans, macrophages, and B cells
. Recognized by T lymphocytes as MHC molecule

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9
Q

Antigen presenting cell mechanism

A

. Initiated when APC ingests antigen (usually protein)
. Ag broken down into small peptide-fragments in cell
. Fragments bind to molecule called histocompatibility complex (MHC)
. Ag-MHC complex is transported to APC surface

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10
Q

MHC in humans also called ____

A

Human leukocyte antigen (HLA)

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11
Q

Population percentage of lymphocytes in circulation in blood or lymph

A

70%

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12
Q

Lymphocyte classification

A

. T cells

. B cells

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13
Q

Lymphocyte general functions

A

. Immunologic surveillance

. Display cell surface receptors that facilitate specific recognition of antigens

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14
Q

T cells

A

. Cell-mediate immunity
. Differentiate in thymus, majority of lymphocytes
. Detect cell-bound Ags presented by MHCs
. T helper cells (Th cells)
. T cytotoxic cells (Tc cells)
. Regulatory T cells

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15
Q

B cells

A

. Humoral immunity
. Differentiate into plasma (antibody-producing)
. Recognize soluble or cell-bound Ags

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16
Q

Antibody

A

. Protein that interacts w/ antigen (Igs do this too)

. Secreted by plasma cells

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17
Q

Reticular cells

A

. In majority of lymphoid tissues/organs

. Produce reticular fibers (collagen III) that for scaffold for lymphoid cells

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18
Q

Epithelioreticular cells

A

. Stellate cells in thymus
. Produce keratins
. Joined by desmosomes

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19
Q

Lymph Nodules

A 
. Densely packed, spherical clusters 
. Embedded in diffuse lymph tissue 
. Not covered by capsule 
. Found in CT 
. Not found in thymus 
. Primary or secondary
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20
Q

Primary nodule

A

. Homogenous

. Formed by small B cells

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21
Q

Secondary nodule

A

. Pale center, darker periphery
. Develop from primary nodules upon Ag stimulation
. Have mantle of just naive B cells

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22
Q

Germinal center of secondary nodule

A

. Dark zone: activated B cells proliferate (centroblasts) and undergo hypermutation where high affinity antibodies enervated
. Light zone: B cells lower profile ration rate and migrate (centrocytes), further differentiate into plasma cells and memory B cells or return to dark zone and become centroblasts again

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23
Q

Primary lymphoid organs

A

. Bone marrow, thymus, fetal liver
. Initial formation of lymphocytes
. Don’t contact Ags

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24
Q

Secondary lymphoid organs

A

. MALT, lymph nodes, spleen
. Cells migrate to here from primary sites
. Lymphocytes activated by encounters w/ Ag to start immune responses
. Ags transported through lymph
. MALT encounters Ags that entered from external environment via M cells

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25
More than 50% lymphoid tissue located in ___
Mucosal system of digestive, respiratory, and GU tracts
26
Lymphocytes in lamina propria
. Mostly activated T cells, sometimes B cells and plasma cells
27
Tonsil lymph tissue
. Waldyer’s ring: diffuse and modular tissue in mucosa . Tonsil epithelium invaginates into underlying lymph to form crypts/pits . Lymph tissue separated by incomplete CT capsule . Only have efferent lymph vessels
28
Types of tonsil
Palatine Lingual Pharyngeal
29
Palatine tonsils
. Btw palatopharyngeal and palatoglossal arches at post. Aspect of oral cavity . Paired . Covered by SSNK
30
Lingual tonsil
. On base of tongue . Paired . Converted by SSNK
31
Pharyngeal (adenoids) tonsil
. In post. Wall of nasopharynx . Unpaired . Psuedostratified ciliated epithelium w/ goblets (respiratory type) . Can hypertrophy and obstruct nasal openings
32
Lymph nodes
. Kidney bean shaped along lymph vessels . Has hilum . Blood vessels enter and leave at hilum, lymph vessels leave at hilum . Surround by dense CT capsule . Capsule sends trabeculae into node where stroma of reticular cells and fibers attach . Macrophages and dendritic cells in reticular fiber network . Afferent and efferent lymph vessels
33
Lymph node parenchyma
. Diffuse and modular lymph tissue divided into cortex/medulla
34
Lymph node cortex
. Area beneath capsule . Outer cortex: diffuse T cells and modular B cells (B-lymphocyte area) . Inner cortex/paracortex: diffuse only, thymus-dependent area, has T cells
35
Lymph node medulla
. Pale staining . Diffuse tissue forms medullary cords (strands) . Cords contain plasma cells, lymphocytes, and macrophages . Cords separated by medullary sinuses
36
Subcapsular (marginal sinus)
. Btw capsule and lymph tissue of outer cortex
37
Trabeculae sinuses
. Cortical/intermediate | . Btw trabeculae and lymph tissue in cortex
38
Medullary sinuses
. Btw medullary cords
39
Afferent lymphatics
. Bring lymph to node for filtering . Come from other organs or other nodes . Numerous vessels pierce capsule of node at periphery to drain subcapsular sinus
40
Efferent lymphatics
. Fewer . Formed by coalescence of medullary sinuses . Exit at hilum and carry lymph away . Efferent lymphatic plus node can become afferent lymphatic of next node
41
T/F lymph flow multidirectional
F, unidirectional, towards hilum
42
Pattern of lymph flow
. Afferent lymphatics -> subcapsular sinus -> cortical sinus -> medullary sinus -> efferent lymphatic
43
Circulation of lymphocytes through nodes
. Some enter lymph, most enter from blood stream in deep cortex area . Cross walls of cuboidalish endothelium of high endothelial post-capillary venules (HEV) by diapedesis . T cells stay in deep cortex . B cells migrate to nodules of superficial cortex
44
HEV cells
. high endothelial cells of lymph nodes . Have surface receptors for lymphocytes . Gate for circulating lymphocytes
45
Lymphadenopathy
. Lymph node enlargement | . Common consequence of infection
46
Lymphoma
. Primary tumor of lymphoid tissue
47
Spleen functions
. Filters blood and detects blood-borne antigens . Removal and destruction of damaged RBCs and platelets . Retrieval of iron from Hb
48
Spleen characteristics
. Largest lymphoid organ . Splenic a. Enters hilum and splenic v. Exits spleen at hilum . Has no direct connections w/ lymph vessels . Lymphocytes enter spleen via blood vessels . Surrounded by dense CT capsule that extends into it via trabeculae . Trabeculae partially divide parenchyma . Rich reticular network . White pulp and red pulp
49
White pulp of spleen
. Lymphoid tissue . Cuff of lymphocytes around central arterioles running through spleen . Accumulations called periarteriolar lymphatic sheaths (PALS) Lymphoid nodules at intervals along PALS that have mostly B cells . Marginal zone of nodule surrounds follicle and is rich in macrophages . Blood borne Ags filtered from blood in marginal zone
50
Arterial circulation in spleen
. Splenic a. Branches into trabecular aa. That follow trabeculae . Become central arterioles after they leave trabeculae and are surrounded by PALS . Some branches of central arterioles end as marginal sinuses that supply marginal zone . Central arterioles lose PALS and terminate as small penicillar aa/ entering red pulp
51
Class I MHC
. Expressed by all nucleated cells | . HLA-A, B, C
52
Class II MHC
. Expressed by APC | . HLA-DR, DQ, DP
53
T helper cells
. CD4+ . Helps via contacts with APCs and other lymphocytes . Help II: helps B lymphocytes to be plasma cells . Helper I: activates macrophages
54
Tc cells
. CD8+ . Cytotoxic functions . Recognition and lysis of virally infected cells
55
T regulatory cells
. CD4+, FoxP3 | . Limit immune response, produce inhibitory cytokines
56
Classes of Ig
``` . IgA: secretory on mucosal surfaces . IgE: basophil cell importance . IgG: most prevalent in blood plasma . IgM . IgD ```
57
NK cells
Kills virally infected cells and tumor cells | Assists Tc cells
58
Frequency for lymphocyte to recognize specific Ag
1 in 10,000 to 100,000 chance | . Even less for both B and T cells to recognize
59
T/F there are reticulocytes I all lymphoid tissue
F, there aren’t in thymus
60
Follicular dendritic cells
. In lymphoid nodules | . Mesenchymal origin, NOT bone-marrow derived
61
Ig class-switch recombination (CSR)
. Centrocytes become plasma cells | 3
62
T/F neutrophils are rare in healthy MALT
T
63
Red pulp of spleen
. Splenic sinusoids and cords (cords of Billroth) . Cords supported by reticular cells/fibers, contain B and T cells, macrophages, plasma cells, dendritic cells, granulocytes, and rbcs . Lined by stave cells
64
Macrophage role in red pulp
. Phagocytosis old rbcs and begin breakdown of Hb and Fe recycling
65
Stave cells
. Loosely connected, elongated endothelial cells . Oriented parallel to blood flow . Spaces btw cells allow blood to leave or enter sinus
66
Closed circulation through red pulp
. Capillaries branching from pencillar arterioles connect directly w/ sinusoids . Blood alway in blood vessel
67
Open circulation in red pulp
. Capillaries from 0.5 penicillar arterioles are open-ended . Blood enters splenic cords . Cells return to circulation by squeezing spaces between stave cells of sinusoid . Platelets, leukocytes, and young rbcs are flexible to do it . Old rbcs are blood from reentry and phagocytosed
68
Thymus embryological origin
. Lymphoid cells from hematopoietic mesenchyme . Stroma made of epithelioreticular cells from endodermal epithelium of 3rd laryngeal pouch (no reticular fiberS) . CT capsule and trabeculae from mesoderm
69
Thymus structure
. In mediastinum . 2 lobes divided into incomplete lobules . CT capsule w/ trabeculae that have blood vessels, nerves, and efferent lymphatics . CT in capsule has reticular fibers and fibroblasts . Cortex w/ thymocytes(dark) . Medulla less cellular (light)
70
Epithelioreticular cells
. Provide framework for T cell development . 6 cel types . Form Hassall’s corpuscles (characteristic of thymus) .
71
Thymic education steps
. T cell precursors from bone marrow enter corticomedullary junction of thymus and migrate to outer cortex (thymocytes) . Thymocytes interact w/ APCs and selected (positive selection) to mature further and enter medulla (10% survive, rest undergo apoptosis) . Thymocytes that would mount immune response against itself is eliminated (neg. selection) in deeper cortex . Cells that made it leave thymus and populate secondary lymphoid organs as naive T cells
72
What mediate positive selection in thymus?
. epithelioreticular cells that display both MHC I and II | .
73
What mediates negative selection in thymic education?
. Bone marrow-derived dendritic cells ad macrophages are main APCs
74
Percentage of thymocytes that survive education process?
2%
75
Thymus Medulla contents
. Paler . Contains fewer cells . Cells larger, have lighter nuclei and more cytoplasm
76
Blood-thymus barrier
. Thymocytes mature into T cells in absence of Ags . Barrier prevents contact btw thymocytes and Ags . Created by endothelium (continuous w/ tight junctions), macrophages in perivascualr tissue, and epithelioreticular cells w/ tight junctions surrounding capillary wall in cortex

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