Immunology - Lymphoid Structures

Question 1

Lymph node

• Characteristics
• Functions

Answer 1

• Characteristics
  
  • A 2° lymphoid organ that has many afferents, 1 or more efferents.
  • Encapsulated, with trabeculae.
• Functions
  
  • Nonspecific filtration by macrophages
  • Storage of B and T cells
  • Immune response activation

Question 2

Follicle

• Characteristics
• 1° vs. 2°

Answer 2

• Characteristics
  
  • Site of B-cell localization and proliferation.
  • In outer cortex.
• 1° vs. 2°
  
  • 1° follicles are dense and dormant.
  • 2° follicles have pale central germinal centers and are active.

Question 3

Medulla

Answer 3

• Consists of medullary cords (closely packed lymphocytes and plasma cells) and medullary sinuses.
• Medullary sinuses communicate with efferent lymphatics and contain reticular cells and macrophages.

Question 4

Paracortex

• Characteristics
• Pathology

Answer 4

• Characteristics
  
  • Houses T cells.
  • Region of cortex between follicles and medulla.
  • Contains high endothelial venules through which T and B cells enter from blood.
• Pathology
  
  • Not well developed in patients with DiGeorge syndrome.
  • Paracortex enlarges in an extreme cellular immune response (e.g., viral infection).

Question 5

Lymph drainage:
Lymph node cluster –> area of body drained

• Cervical
• Hilar
• Mediastinal
• Axillary
• Celiac
• Superior mesenteric
• Inferior mesenteric
• Internal iliac
• Para-aortic
• Superficial inguinal
• Popliteal
• Right lymphatic duct
• Thoracic duct

Answer 5

• Cervical
  
  • Head and neck
• Hilar
  
  • Lungs
• Mediastinal
  
  • Trachea and esophagus
• Axillary
  
  • Upper limb, breast, skin above umbilicus
• Celiac
  
  • Liver, stomach, spleen, pancreas, upper duodenum
• Superior mesenteric
  
  • Lower duodenum, jejunum, ileum, colon to splenic flexure
• Inferior mesenteric
  
  • Colon from splenic flexure to upper rectum
• Internal iliac
  
  • Lower rectum to anal canal (above pectinate line), bladder, vagina (middle third), prostate
• Para-aortic
  
  • Testes, ovaries, kidneys, uterus
• Superficial inguinal
  
  • Anal canal (below pectinate line), skin below umbilicus (except popliteal territory)
• Popliteal
  
  • Dorsolateral foot, posterior calf
• Right lymphatic duct
  
  • Right side of body above diaphragm
• Thoracic duct
  
  • Everything else into junction of left subclavian and internal jugular veins

Question 6

Sinusoids of spleen

• Sinusoids
• Where T cells are found
• Where B cells are found
• Marginal zone

Answer 6

• Sinusoids
  
  • Long, vascular channels in red pulp with fenestrated “barrel hoop” basement membrane.
  • Macrophages found nearby.
• Where T cells are found
  
  • In the periarterial lymphatic sheath within the white pulp of the spleen.
• Where B cells are found
  
  • In follicles within the white pulp of the spleen.
• Marginal zone
  
  • In between the red pulp and white pulp
  • Contains APCs and specialized B cells
  • Where APCs present blood-borne antigens

Question 7

Sinusoids of spleen

• Function of macrophages in the spleen
• Splenic dysfunction
• Postsplenectomy

Answer 7

• Function of macrophages in the spleen
  
  • Remove encapsulated bacteria.
• Splenic dysfunction
  
  • e.g., postsplenectomy, sickle cell disease
  • Decreased IgM –> decreased complement activation –> decreased C3b opsonization –> increased susceptibility to encapsulated organisms
  • SHiNE SKiS:
    
    • Streptococcus pneumoniae
    • ƒƒHaemophilus influenzae type B
    • ƒƒNeisseria meningitidis
    • Escherichia coli
    • Salmonella spp.
    • Klebsiella pneumoniae
    • ƒƒGroup B Streptococci
• Postsplenectomy:
  
  • ƒƒHowell-Jolly bodies (nuclear remnants)
  • Target cells
  • Thrombocytosis

Question 8

Thymus

• Characteristics
• Sections

Answer 8

• Characteristics
  
  • Site of T-cell differentiation and maturation.
    
    • T cells = Thymus
    • B cells = Bone marrow
  • Encapsulated.
  • From epithelium of 3rd pharyngeal pouches.
  • Lymphocytes of mesenchymal origin.
• Sections
  
  • Cortex is dense with immature T cells
  • Medulla is pale with mature T cells and Hassall corpuscles containing epithelial reticular cells.