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Histology > Lymphoid Tissue (B 2 : W 1) > Flashcards

Lymphoid Tissue (B 2 : W 1) Flashcards

1
Q

What is the difference between innate and adaptive immunity?

A
  • Innate (natural)
    • Epithelia (physical barrier)
    • Phagocytic cells (macrophages and neutrophils)
    • Natrual killer cells
    • Blood proteins: complement system
  • Adaptive (acquired or specific)
    • Humoral immunity (antibody mediated)
      • B cells and plasma cells
    • Cell mediated (cellular immunity)
      • T cells
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2
Q

What are lymphocytes?

A
  • B cells
  • T cells
  • Natural killer cells
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3
Q

What are natural killer cells?

A

Cell population lacking T cell receptor (TCR) and CD4 and CD8 co-receptors

  • T-like lymphocytes that do not enter the thymus - immunocompetent on their own
  • Act non-specifically
  • Produce perforins and **granzimes **
    • Chew through cell membrane
    • Destroy cell from inside out
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4
Q

What are the accessory cells in immune reactions (non-lymphocytes)?

A
  • Macrophages - either antigen presenting OR phagocytic
  • Dendritic cells - fibroblast-like cells that form the stroma of lymphatic tissue
  • Epithelial reticular cells - exclusively in _thymus _
  • Antigen presenting cells (APC)
    • Express MHCI and MCHII on plasmalemma
    • Phagocytose, catabolize, process, present antigen
    • Produce cytokines
    • Many belong to mononuclear phagocytic sytem
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5
Q

What are the characteristics of T cell lymphocytes?

A
  • Responsible for cell-mediated immunity against antigens likemicroorganisms, virus-infected cells, tumors, and transplant cells
  • Able to differentiate between self and antigen
  • Found in T dependent regions of the body (and other regions)
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6
Q

Where do T cells originate? Where do they differentiate and become immunocompetent?

A

T cells originate in bone marrow

Differentiate and become immunocompetent in thymus

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7
Q

T cells are found in various regions of the body. What are the two T-dependent regions?

A
  1. Paracoritcal regions of the lymph nodes
  2. Periarterial sheaths of the spleen
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8
Q

Native T cells are immunocompetent but still must be activated. What happens once they are activated?

A

Activated T cells divide by mitosis and become

  • Memory T cells
    • Responsible for the immunological memory of the adaptive system
  • Effector T cells
    • T helper cells (recognition of foreign atigens)
    • Cytotoxic T cells (responsible for killing foreign cells, tumor cells, and virus infected cells)
    • Suppressor T cells (suppress the immune response of other T lympocytes)
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9
Q

What are the characteristics of B lymphocytes?

A
  • Response for antibody mediated immunity
  • Found in all lymphoid tissue (very few in thymus)
  • Upon antigen stimulation, B lymphocytes proliferate and differentiate into
    • Plasma cells - Primary response
    • Memory B cells - Secondary response
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10
Q

How do B cells become activated?

A

B cells require interaction with helper T cells to become activated and differentiate into plasma cells

Upon antigen stimulation, B lymphocytes proliferate and differentiate

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11
Q

Where do B cells originate and mature?

A

Bone marrow

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12
Q

What is the role of plasma cells?

A
  • Synthesize and secrete antibody to specific and group antigens
  • Primary response
  • Antibodies: IgA, IgD, IgE, IgG, IgM
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13
Q

Which antibody is most abundant in serum?

A

IgG

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14
Q

Which antibody is most abundant in gladular secretions (i.e. intestinal mucosa)?

A

IgA

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15
Q

What is the role of B memory cells?

A
  • Responsible for immunological memory (just like memory T)
  • Secondary response
  • Long term immunity (mantle layer lymph node)
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16
Q

Which antibody crosses the placental barrier?

A

IgG is the only antibody that crosses the placental barrier, due to size

Responsible for imparting acquired immunity to the fetus

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17
Q

Which is the choice immunoglobulin in mucosa?

A

IgA - synthesized in mucosa

  • Mucosa produces J-protein unit that attaches to IgA so that it’s not degraded by the mucosa
  • Found in anything in contact with outside - GI, GU, respiratory
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18
Q

What is the difference between stroma and parenchyma?

A
  • Stroma is the scaffolding that is found within the organ
    • Usually connective tissue fiber
  • Parenchyma is the functional unit that fits in the stroma
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19
Q

What is the stroma of the lymphatic system?

A

Reticular fibers (collagen III) - Agyrophilic, branching

Can also be dendritic cells, or epithelial reticular cells (thymus)

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20
Q

What is the parenchyma of the lymphatic system?

A

T and B lymphocytes, macrophages, APCs, etc

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21
Q

What are the functions of the lymphatic system?

A
  • Concentrate and eliminate antigens
  • Production and maturation of lymphocytes
  • Addition of antibodies
  • Provides a means for returning tissue fluid back into the blood stream
  • Allows for absorption of chylomicrons from small intestine
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22
Q

Where do lymphocytes undergo antigen-independent differentiation?

A

Primary lymphatic organs

Thymus and bone marrow

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23
Q

Where do lymphocytes undergo anigen-dependent activation?

A

Secondary lymphatic organs

Diffuse lymphatic tissue, tonsils, lymph nodes, spleen

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24
Q

What role do dendritic cells play in the lymphatic system?

A
  • Can act as antigen presenting cells
  • Make reticular fibers (look and act like fibroblasts)
25
Q

What are the two roles of macrophages in the lymphatic system?

A
  • Phagocytic cells
  • Antigen presenting cells (which is non-phagocytic)
26
Q

What are the characteristics of lymphatic vessels?

A
  • Thin walled, endotehlial lined, some smooth muscle in larger vessels and thoracic duct
  • Absent from avascular structures (hair, nails, cornea, cartilage), the CNS, and bone marrow
  • Afferent and efferent vessels
27
Q

Where is diffuse lymphatic tissue found?

A

Lamina propria of all mucosas that are in contact with the outside world

28
Q

What are M cells and what do they do?

A

Special cells within mucosa - microfold or mucosal cells

Antigen presenting cell

Capture luminal antigens and transport them to lymphocytes, macrophages, and dendritic cells

Dome-shaped, present in the covering of Peyer’s patches in intestines

29
Q

What happens when macrophages and dendritic cells presenting antigens go to lymph nodes?

A

Stimulate B and T lymphocytes

B and T cells enter lymphatic circulation and later blood cericlation

Home in other tissues, including mucosa lamina propria, where plasma cells produce large amounts of IgA

Lymphoid cells of lamina propria are a major antibody producer, because of their extension and close contact with antigens introduced into the digestive tract

30
Q

Where are lymphatic nodules composed of?

A
  • B cells
  • Lymphoblasts
  • Plasma cells
  • Memory cells

Very few T cells

31
Q

What is the difference between a primary lymphatic nodule and a secondary lymphatic nodule?

A
  • Primary = Has not seen antigen
  • Secondary = Has seen antigen
    • Have germinal centers - cleared out appearance, undergoing mitosis
    • Central region lighter due to proliferation of lymphoblasts
32
Q

What does it mean that lymphatic nodules can be transitory?

A

Not associated with connective tissue

  • Lymphatic nodules never have a connective tissue capsule
33
Q

Where are Peyer’s patches of lymphatic nodules?

A

Ileum

Start in lamina propria and extend into submucosa

34
Q

What are the characteristics of tonsils?

A
  • Aggregate of nodules (secondary) grouped around crypts
  • Possess M cells (antigen presenting cells)
  • No afferent lymphatic vessels, only efferent
  • Possess an incomplete capsule of connective tissue which acts as a protective barrier against leakage of antigen into pharyngeal CT spaces
    • Physical barrier - part of innate immunity
35
Q

What is Waldeyer’s ring?

A

Circular band of tonsils protecting the openings of GI and respiratory tracts

Both in contact with outside world

36
Q

What are the major tonsils and their epithelia?

A
  • Palatine - stratified squamous
  • Lingual - stratified squamous
  • Nasopharyngeal - respiratory
37
Q

What are characteristics of lymph nodes?

A
  • NOT glands
  • Situated in course of lymph vessels - lymph nodes are filters of lymph
  • Bean-shaped
  • Have a cortex and medulla
  • Maintain and produce T and B cells
  • Have APCs and macrophages
38
Q

Where do afferent and efferent vessels enter and leave the lymph node capsule, respectively?

A
  • Afferent lymphatics enter the capsule
  • Efferent lymphatics leave via the hilum
39
Q

Where are T cells found in lymph nodes?

A

Paracortical regions

40
Q

Know this structure

A

Pay special attention to the medullary sinuses

Medullary cords surround medullary sinuses

41
Q

What are high endothelial cells and where can they be found?

A

Allow passage of lymphocytes from capillaries to efferent lymph vessels, then back into blood

Found on the post-capillary side of the capillary network in lymph nodes

42
Q

What is the approximate distribution of T and B lymphocytes?

A
43
Q

Where does the thymus come from?

A

Endoderm (epithelial reticular cells) and mesoderm (lymphocytes)

44
Q

Does the thymus have germinal centers?

A

No - 99% T cells

45
Q

What are unique characteristics of the thymus?

A
  • Function is maturation and differentiation of T cells (thymocytes)
  • Growth until mid-teens, then fat accumulation
  • No afferent lymphatics
  • Has a cortex and medulla with lobules
  • 6 types of epithelial-reticular cells
    • 1-3 in cortex
    • 4-6 in medulla
46
Q

What is the stroma in the thymus?

A

Epithelial reticular cells, which contain tingible (stainable) body macrophages

47
Q

What are the functions of the epithelial reticular cells in the thymus?

A
  • Participate in the blood-thymic barrier
  • Produce 4 hormones necessary for T cell maturation
    • No other lymphatic organ produces hormones
  • Possess desmosomes and tonofilaments
48
Q

What layers make up the blood thymic barrier?

A
  • Capillary endothelium
  • Capillary basal lamina
  • CT sheath of the capillary
  • Epithelial reticular cell basal lamina
  • Epithelial reticular cells
49
Q

What happens in the cortex of the thymus?

A
  • T cell maturation and differentiation - become immunocompetent
  • Elimination of intolerant T cells (98% are eliminated)
50
Q

What is found in the thymic medulla?

A
  • Hassall’s corpuscles (swirls) - Hallmark of the thymus
  • Immunocompetent T cells
  • Some B cells, but no germinal centers
51
Q

What are uniqu characteristics of the spleen?

A
  • Left hypochondrium
  • Possibly largest lympoid organ in the body (other than intestines)
  • No afferent lymphatics
  • Surrounded by a fibrous capsule containing some smooth muscle
  • Red and white pulps within the parenchyma
    • Red pulp - blood filter
    • White pulp - immunological filter
52
Q

What are the functions of the spleen?

A
  • Immunological filter of blood
  • Blood reservoir
  • Phagocytosis of damaged and aged RBCs
  • Proliferation of B and T cells
  • Production of atibodies by plasma cells
53
Q

What are trabeculae in the spleen?

A

Trabeculae from capsule break up the parenchyma (splenic pulp) into incomplete compartments

54
Q

What is uniqe about white pulp of the spleen?

A

Consists of lymphatic nodules that have blood vessel associated with them

  • Ecentric arterioles
    • Periarteriole lymphatic sheath surrounds aretery in nodule - consists of T lymphocytes
  • Have germinal centers
55
Q

Does spleen have a cortex and medulla?

A

No, just red and white pulp

56
Q

What are splenic sinusoids and splenic cords?

A
  • Splenic sinusoids (capillaries that are blown up)
  • Splenic cords (Cords of Billroth) - separate out the sinusoids
    • Contain lymphocytes, dendritic APCs, reticular fibters, blood vessesl, macrophages
57
Q

How do spleic sinusoids clear out old and damaged RBCs?

A
  • Open circulation (picture)
    • Blood comes in
    • Sinusoid is so leaky that blood percolates - moves through sinusoid
    • Macrophages remove old RBCs
  • Closed circulation
    • RBCs on inside of sinusoid, macrophages on outside
    • Macrophage pseudopodia reach in an feel for old RBCs
    • Old ones are pulled out and phagocytized in the cords

Humans really use both

58
Q

Know structures in these pictures

A

Pay attention to ecentric arterioles in germinal centers

Cords vs. sinusoids

Histology (5 decks)

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