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Histology > Lymphoid system > Flashcards

Lymphoid system Flashcards

0
Q
  1. ) Where do lymphocytes originate?
  2. ) Where do lymphocytes become mature (2 places)?
  3. ) Where does their activation and proliferation occur (5)?
A
  1. ) Red bone marrow
  2. ) Primary lymphoid organs: Thymus (T cells) and bone marrow (B cells).

3.) Secondary lymphoid organs:
1.) The lymph nodes
2.) Spleen
Diffuse lymphoid tissue of the mucosa in the digestive system, including:
3.) Tonsils
4.) Peyer patches
5.) Appendix

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1
Q

Name and describe the two types of immunity.

A
  1. ) Innate: IMMEDIATE, nonspecific (works against wide groups of agents), evolutionarily older.
  2. ) Adaptive: Mediated by T and B lymphocytes, and ANTIGEN-PRESENTING CELLS (APCs) and memory cells. Aims at specific microbial invaders.
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2
Q

What are some tissue/organisms involved in innate immunity (4)?

A
  1. ) Physical barriers: skin, mucous membranes of the GI, respiratory, and urogenital tracts.
  2. ) Neutrophils and other leukocytes
  3. ) Toll-like receptors (TLRs) on leukocytes allow recognition and binding of surface components of such invaders.
  4. ) Natural killer cells
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3
Q

How do some pathogenic bacteria avoid phagocytosis by granulocytes and macrophages of innate immunity?

A

By covering their cell walls with a polysaccharide capsule, thereby inhibiting recognition and binding to the phagocytes receptors –> p.264 Junq

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4
Q

What are APCs usually derived from?

A

Monocytes –> p.264, but p.101 DESCRIBES THEIR LINEAGE!!!

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5
Q

Which type of immune response are cytokines involved in? What do they do?

A

Both innate and adaptive. They help immune cells communicate to coordinate defensive measures.

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6
Q

Name and describe four types of antigen presenting cells (APCs) involved in adaptive immunity

A

p. 268 Junq
1. ) Dendritic cells of lymphoid organs
2. ) Epithelial reticular cells of thymus
3. ) Macrophages
4. ) B Lymphocytes

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7
Q

Stem cells for all lymphocytes are born in ________.

A

Red bone marrow

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8
Q

Name three secondary lymphoid sites

A
  1. ) Lymph nodes
  2. ) Spleen
  3. ) Mucosa associated lymphoid tissue (MALT)
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9
Q

Lymphoid tissue is usually _______ tissue with large numbers of ____ and ______ cells.

A

Reticular connective tissue with large numbers of lymphocytes and antigen presenting cells.

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10
Q

How are lymphocytes distinguished from one another (2)?

A

Morphologically indistinguishable.

  1. ) Must use special stains to identify surface proteins/markers (CD markers) or…
  2. ) Other key surface proteins, including B-Cell receptors and T-Cell receptors..
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11
Q

B cells interact with ______ and aggregate as a primary lymphoid nodule. How?

A

p.271
Follicular dendritic cells (FDCs). IN ALL SECONDARY LYMPHOID TISSUES, B lymphocytes interact with these. Surfaces of these cells are covered with antibody-antigen complexes bound to receptors for compliment proteins causing B cells to attach, become activated, and aggregate as a small PRIMARY lymphoid nodule (or follicle). With the help of adjacent Th cells, these B cells now form a much larger and more prominent secondary lymphoid nodule.

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12
Q

Where do antibodies come from?

A

They are secreted by PLASMA CELLS that arise by terminal differentiation of clonally proliferating B lymphocytes.

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13
Q

Describe the general design of the immunoglobulin of antibodies

A

A glycoprotein consisting of two identical light chains, and two identical heavy chains that are bound by disulfide bonds.

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14
Q

Where is the variable region of an antibody located?

A

On the first 110 amino acids near the AMINO-TERMINAL end of the light and heavy chains.

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15
Q

B lymphocytes differentiate into 1.)______, which accumulate in 2.) ________.

A
  1. ) Plasma cells

2. ) Medullary cords

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16
Q

What are two features common to all antigen-presenting cells (APCs)?

A

p. 268
1. ) An active endocytotic system
2. ) Expression of MHC class II molecules for presenting peptides of exogenous antigens.

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17
Q

What is the primary/central lymphoid organ in which T cells are produced? What is it derived from and what is its main function?

A

p.273
Thymus: It is derived from the embryo’s THIRD PAIR OF PHARYNGEAL POUCHES (endoderm). Its main function is the induction of CENTRAL TOLERANCE, which, along with T cells, PREVENTS AUTOIMMUNITY.

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18
Q

What is the ultimate fate of the thymus in adults?

A

It is fully functional at birth and remains active until puberty. It then undergoes INVOLUTION, decreasing greatly in size and activity and becoming largely filled with ADIPOSE TISSUE.

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19
Q
  1. ) What is a transient characteristic of all secondary lymphoid organs?
  2. ) How to tell the difference between a.) primary and b.) secondary nodules?
A

p. 272
1. ) Large aggregates of B cells (called lymphoid nodules or follicles).
2. ) a.) Primary nodules: B cell aggregates of uniform cell density and staining.
b. ) Secondary nodules: Larger, more euchromatic cells located centrally (GERMINAL CENTERS), with smaller naive lymphocytes pushed peripherally (FOLLICULAR MANTLE).

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20
Q

Describe the structure of the thymus, with emphasis on its lobules.

A
  • A bilobed structure in the mediastinum.
  • Has a vascularized connective tissue capsule that extends septa into the parenchyma, thus dividing the organ into many INCOMPLETELY SEPARATED LOBULES.
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21
Q

Describe the composition of lobules in the thymus

A

Each lobule has an outer darkly basophilic CORTEX that surrounds the more lightly stained MEDULLA.

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22
Q

Describe the cells associated with the thymic cortex (2)

A
  1. ) An extensive population of T lymphoBLASTS (aka THYMOCYTES) located among numerous macrophages and associated with… –>
  2. ) Thymic epithelial cells (TECs): Have features of both epithelial and reticular cells. They usually have large EUCHROMATIC NUCLEI.
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23
Q
  1. ) Describe the histologic presentation of the THYMIC MEDULLA and…
  2. ) Describe Hassall corpuscles
A
  1. ) More lightly staining than the cortex. Contains fewer and larger, more mature lymphocytes.
  2. ) Hassall corpuscles: Large aggregates of TECs, sometimes concentrically arranged (concentric “whirl”). Thymic corpuscles are UNIQUE TO THE THYMIC MEDULLA and secrete several cytokines that control activity of local dendritic cells, including factors that promote development of regulatory T cells for peripheral tolerance
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24
Q

What is the relationship between T cells and reticular epithelial cells of the thymus?

A

Epithelial cells secrete a variety of hormones which are important in the maturation of T lymphocytes.

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25
Q

Why is the two-stage, thymocyte-mediated maturation process of T cells in the thymus so important?

A

It ensures that mature T cells have T cell receptors that are FUNCTIONAL, but DO NOT BIND SELF-ANTIGENS –> p.275

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26
Q

Describe positive selection of T cells. What must T cells be able to do in order to complete this process?

A

It describes the process where the survival of T cells depends on whether they develop functional antigen receptors (i.e. they must be able to recognize peptides bound to MHC class 1 or 2 molecules) –> p.275

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27
Q

Describe negative selection of T cells

A

Development of T cells that focuses on removing T cells whose TCRs strongly bind self-antigens –> p.275

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28
Q
  1. ) What is central tolerance?

2. ) Peripheral tolerance?

A

WIKI
1.) It is the mechanism by mechanism by which newly developing T and B cells are rendered NON-REACTIVE TO SELF. It occurs while developing immune cells ARE STILL PRESENT IN THE PRIMARY LYMPH ORGANS.

2.) Peripheral tolerance is generated AFTER the cells reach the periphery by REGULATORY T cells.

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29
Q

Describe the tonsils and the three types.

A

Masses of LYMPHOID TISSUE in the mucosa of the posterior oral cavity and nasopharynx.

  1. ) Palatine
  2. ) Lingual
  3. ) Pharyngeal
30
Q

What is the purpose of MALT?

A

p. 276
They are secondary lymphoid structures that protect the mucosa (i.e. inner lining of the digestive, respiratory, and GU tracts), which is a common site of invasion by pathogens because their lumens face the external environment

31
Q

What is a Peyer’s Patch. Describe. Why are they necessary?

A

(10.57 Wilson, p.278 Junq)
Lymphoid tissue in mucosa and submucosa of the ilium and appendix. Causes elevations of the mucosal surface of the ilium. They are needed because there is an abundance of pathogens in the GI tract.

32
Q

What are M cells? Describe their composition.

A

Large epithelial cells at apical surface of intestines over Peyer’s patches with apical microfolds rather than a brush border. On their basal side there are large intracellular pockets that contain transient populations of lymphocytes and dendritic cells and open to the underlying lymphoid tissue through a highly porous basement membrane. Antigens in the intestinal lumen are continuously sampled at the apical surface of these cells are transferred to the immune cells in the pockets

33
Q

What type of lymph tissue is in the appendix? Describe it.

A

The appendix contains a significant collection of MALT in its mucosa.

The appendix is a short, small-diameter projection from the cecum. Typically, the mucosa of the appendix is almost completely filled with lymphoid tissue.

34
Q
  1. ) Where are lymph nodes found?

2. ) What do they do?

A
  1. ) Occur along the course of lymphatic vessels throughout the body. 2.) They filter lymph as it drains back to the blood stream.
    - Enlarge when an immune response is initiated.
    - Provide enclosed environment that facilitate production of plasma cells secreting non-IgA antibodies.
35
Q
  1. ) On what surface of the lymph nodes do the afferent lymphatics enter?
  2. ) Where do the blood vessels enter?
A
  1. ) The convex surface.

2. ) Concave surface

36
Q

Describe the components of the cortex of a lymph node (2)?

A
  1. ) Lymphatic nodule: Immediately inside the capsule, receives lymph from the afferent lymphatics. With or without germinal centers, fill most cortical areas, FORMED LARGELY BY HELPER T LYMPHOCYTES and proliferating B LYMPHOBLASTS. —> Germinal center: Site of B cell activation (undergoing lymphoblastic transformation), clonal expansion, and differentiation.
  2. ) Cortical sinuses (or trabecular sinuses): Branch internally among the lymphoid nodules along trabeculae. Lymph passes through these sinuses and percolates easily into the surrounding lymphoid tissue.
37
Q

What is the directionality of lymph flow? How?

A

Unidirectional via valves in the lymphatics.

38
Q

What are the most abundant cells in lymph nodes?

A

Lymphocytes of all types: Plasma cells, dendritic cells, macrophages, and other APCs. FDCs (follicular dendritic cells)

39
Q

What are the three main regions of a lymph node?

A
  1. ) An outer CORTEX
  2. ) A central MEDULLA
  3. ) PARACORTEX (lies between the prior two): No precise boundaries, but can be distinguished from outer layer by its lack of B-cell lymphoid nodules.
40
Q

How does the paracortex of the lymph nodes differ from the superficial cortex?

A

The paracortex contains lymphoid tissue rich in T cells that can be seen by IMMUNOHISTOCHEMISTRY

41
Q

Where do 90% of lymphocytes enter the lymph nodes? What are they? Describe.

A

High endothelial venules (HEVs): Specialized postcapillary venules in the PARACORTEX which facilitate the movement of lymphocytes THROUGH THE WALL OF THE VENULE INTO THE LYMPH NODE (i.e. blood-to-lymph movement). They have an endothelial lining of cuboidal cells.

42
Q

Describe the two major components of the lymph node medulla

A

p. 279
1. ) Medullary cords: Branched, cord-like masses extending from the paracortex. They contain B and T lymphocytes and many plasma cells.

2.) Medullary sinuses: Dilated spaces lined by discontinuous endothelium that separate the medullary cords. Continuous with the cortical sinuses and converge at the hilum as the efferent lymphatic vessel. The lumen contains a meshwork of processes from reticular cells which represent a final lymph filter. THE SINUSES WILL CONTAIN MANY MACROPHAGES AND SOMETIMES NEUTROPHILS IF THE LYMPH NODE IS DRAINING AN INFECTED REGION

43
Q

What is/are the main role(s) of the spleen?

A
  1. ) Activation of immune cells to antigens in the blood.
  2. ) Disposal of senescent blood cells, ESPECIALLY RBCs.
  3. ) Hematopoiesis in fetus (and sometimes adults with hematopoietic diseases).
44
Q

What are the components of splenic pulp (2). Describe.

A

p. 281-282 (Spleen)
1. ) White pulp (20%): Consist of lymphatic nodules and the periarteriolar lymphoid sheaths (PALS) surrounding central arterioles.

2.) Red pulp: Consists of blood-filled sinusoids and splenic cords.

45
Q

The spleen is a(n) ______ lymphoid organ.

A

Encapsulated

46
Q

What is the difference between the sinusoids of the spleen and lymph nodes?

A

Lymph node sinusoids contain lymph, spleen sinusoids contain BLOOD.

47
Q

What forms the framework of the splenic core? How is it viewed histologically?

A

Reticular connective tissue viewed with special stains (reticulin stain).

48
Q
  1. ) What does the splenic white pulp consist mainly of?

2. ) PALS?

A
  1. ) Mostly B cells

2. ) Mostly T cells.

49
Q

Describe the possible blood flow through red pulp of the spleen

A
  1. ) Closed circulation: Blood directed into the splenic sinus directly from blood vessel (arteriole).
  2. ) Open circulation: Blood dumps out of arteriole AROUND THE SPLENIC SINUS and enters into the splenic sinus through gaps around the sinus.
50
Q

Where and how are RBCs removed within the spleen?

A

p.284-285
Where: They are removed by STAVE CELLS in the sinusoids that separate the SPLENIC CORDS (of Billroth) within the red pulp.

How: In open circulation, the blood must reenter the vasculature through narrow, barrel-like slits between the stave cells. These slits present no obstacle to platelets or motile RBCs. Stiff or effete RBCs (after 120 days), however, are blocked from passing through the stave cells are are selectively removed by macrophages.

51
Q

Describe the general characteristics, lineage, and role of macrophages

A

p.122
They are short-lived cells that differentiate in connective tissue from precursor MONOCYTES circulating in the blood.

Functions:

  • ECM turnover
  • Phagocytosis of dead cells and debris
  • ANTIGEN PROCESSING/PRESENTATION TO LYMPHOCYTES
  • Production of cytokines, chemotactic factors (molecules that participate in inflammation)
52
Q

What is the relationship between monocytes and macrophages?

A

Macrophages are derived from monocytes. They are the same cell at different stages of development. p.101

53
Q

What are the family of cells derived from monocytes called?

A

Mononuclear phagocyte system p.101

54
Q

Give 4 examples of macrophages with different names and their associated organs

A
  1. ) Kupffer cells in the liver
  2. ) Microglial cells in the CNS
  3. ) Langerhans cells in the skin
  4. ) Osteoclasts in the bone tissue
    p. 101
55
Q

What are some general functions of mast cells? Staining?

A
  1. ) Local inflammatory response
  2. ) Innate immunity: Release cytokines to direct leukocytes and other immune cells.
  3. ) Tissue repair
  4. ) Promotion of allergic reactions: Histamine.

Filled with basophilic secretory granules

56
Q

Where do the different lymphocytes originate from?

A

p.268
In adults, STEM CELLS FOR ALL LYMPHOCYTES are located in the RED BONE MARROW. But the cells of lymphoid lineages mature and become functional in TWO different central/primary LYMPHOID ORGANS –> Bone marrow (B cells), and the Thymus T cells).

57
Q

Which cell-types are APCs?

A

p. 268
- ALL monocyte-derived cells.
- “Professional” APCs: Epithelial reticular cells of the thymus, and B lymphocytes.
- “Nonprofessional” APCs: Fibroblasts and vascular endothelial cells.

58
Q

Reticular fibers support the cells of most lymphoid tissue and organs, except in the….

A

p.269

Thymus

59
Q

Where are you likely to find GERMINAL CENTERS and their corresponding MANTLES? Describe.

A

In secondary lymphoid nodules (MALT, lymph nodes, spleen)

60
Q

Describe the appearance of a thymic lobule

A

(p.272 and fig.14-6)
Each lobule has a darkly BASOPHILIC CORTEX (due to greater density of lymphoblasts and small lymphocytes), surrounding a more LIGHTLY STAINED MEDULLA.

61
Q

Describe the location, composition, and function of Hassall corpuscles

A

Unique to the THYMIC MEDULLA. They consists of large aggregates of THYMIC EPITHELIAL CELLS (TECs) [p.272].

These cells secrete several cytokines that control the activity of local dendritic cells, including factors that promote development of regulatory T cells for peripheral tolerance. p.273

62
Q

What is the function and main locations of dendritic cells?

A

p.102

Antigen processing and presentation in the lymph nodes and spleen.

63
Q

What is the function and main locations of Langerhans cells?

A

p.102

Antigen processing and presentation in the epidermis of the skin

64
Q

What is the function and main locations of Kupffer cells?

A

p.102
Same function as macrophages (production of cytokines, chemotactic factors, and several other molecules that participate in inflammation (defense), antigen processing, and presentation. They are located in the LIVER (perisinusoidal)

65
Q

What is the function and main locations of monocytes?

A

p.102

The function as precursors to macrophages in the BLOOD.

66
Q

What are the main functions and locations of macrophages?

A

p.102
They function in the production of cytokines, chemotactic factors, and several other molecules that participate in inflammation (defense), antigen processing, and presentation. They are located in connective tissue, lymphoid organs, lungs, bone marrow, pleural and peritoneal cavities.

67
Q

What are two features common to ALL APCs?

A

p. 268
1. ) An active endocytotic system
2. ) Expression of MHC class II molecules for presenting peptides of exogenous antigens.

68
Q

Positive selection occurs in the ____ and allows for survival only of T cells with functional TCRs that recognize which MHC class(es)?

A

Occurs in the CORTEX (outer portion).
MHC class 1 and 2.
Bottom of p.275

69
Q

How to distinguish TONSIL histology

A

(p.277 Junq, 10.36 Wilson)
Epithelium: Stratified squamous.

Crypts: Infoldings of the mucosa. Along the periphery and beneath the epithelium of the crypts, NODULES are especially numerous. Epithelium along crypts is desquamated.

70
Q

How to histologically distinguish the jejunum from other sections of small intestine?

A
  1. 57 Wilson
    - Extra long villi
    - Absence of –> SUBMUCOSAL GLANDS and PEYER’S PATCH
71
Q

Where is the subcapsular sinus in a lymph node and what does it do?

A

It is immediately inside the capsule and receives lymph from AFFERENT lymphatics. p.279

72
Q
  1. ) What type(s) of cell(s) is/are found in the medullary lymph cords?
  2. ) What separates the lymph cords?
A
  1. 15 Wilson
  2. ) Lymphocytes, plasma cells, macrophages.
  3. ) Medullary sinuses which drain into efferent vessels.
73
Q

The majority of lymphocytes enter the lymph nodes via what? Where can these be seen within the lymph nodes?

A

Post-capillary venules. They can be seen within the medullary cords. 10.16 Wilson

Histology (9 decks)

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