Lymph nodes

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The lymph node, abbreviated LN, is very important in pathology. It is the site of mets and may be the site of a primary lesion, i.e. lymphoma.

Haematopathology and lymphoma is dealt with in the haematopathology article. This article covers the basics of LNs.

LN architecture

Lymph node architecture (superficial to deep):[1]

  • Capsule.
  • Subcapsular sinus.
    • Place where metastatic cells often are found.
  • Cortex:
    • Follicles (superficial).
    • Paracortex (deep).
    • Cortical sinuses.
  • Medulla:
    • Medullary cords.
    • Medullary sinuses.

Notes:

  • Trabeculae - segment the LN radially, i.e. are spoke-like structures.

LN follicles

Types of follicles:[2]

  1. Primary follicle - no germinal center (pale area).
  2. Secondary follicle - have a germinal center (pale area) and mantle zone (rim of darker staining lymphocytes).

Germinal centre

Architecture:

  • Paler at capsular aspect.
  • Darker at medullary aspect.

Location and cell types

Germinal centers:[3]

  • Site of B lymphocyte proliferation; follicle center cells.
    • Centrocytes transforming to immunoblasts (superficial aspect - paler).
    • Centrocytes (mid germinal center).
    • Centroblasts (deeper aspect - darker).
  • Tingible body macrophages - mid germinal center.
  • Follicular dendritic cells.

Paracortex:[4]

  • Site of T lymphocytes.
  • Interdigitating dendritic cell.

Medullary cords (site of immunoglobulin synthesis):

  • B lymphocytes.
  • Plasma cells.

Mantle zone:

  • Memory B cells.

B cell cycle

B cell cycle/maturation:[5]

  1. Centroblast (CB):
    • Appearance:[6]
      • Large cells.
      • Round nucleus, dark.
      • Nucleolus (nucleoli).
      • Mitotically active.
    • Location:
      • Medullary aspect of germinal center.
  2. Centrocytes (CC), AKA cleaved cells.
    • Appearance:
      • Cleaved nucleus
      • NOT mitotically active.
    • Location:
      • Mid germinal center.
  3. Immunoblasts or memory B cells.
    • Appearance:
      • Small lymphocytes.
    • Location:
      • Peripheral blood, mantle zone.

Notes:

  • Immunoblasts may be T cells or B cells; it is not possible to tell on morphologic grounds, i.e. without IHC.

Image:

Cell types

Follicular dendritic cells:[7]

  • Classically found in pairs.
  • Large nucleus with:
    • Basketweave chromatin pattern.
    • Small central nucleolus.

Lymphocytes

  • See B cell cycle section.

See also

External links

References

  1. Wheater's FH. 4th Ed. PP.206-8.
  2. Wheater's FH. 4th Ed. P.208.
  3. Wheater's FH. 4th Ed. P.210.
  4. Wheater's FH. 4th Ed. P.211.
  5. Wheater's FH. 4th Ed. P.210.
  6. URL: http://www.healthsystem.virginia.edu/internet/hematology/HessEDD/BenignHematologicDisorders/normal-hematopoietic-cells/Secondary-lymphoid-organs-and-tissues.cfm. Accessed on: 31 January 2010.
  7. Wright CA, Nayler SJ, Leiman G (August 1997). "Cytopathology of follicular dendritic cell tumors". Diagn. Cytopathol. 17 (2): 138–42. PMID 9258622. http://www3.interscience.wiley.com/journal/57062/abstract?CRETRY=1&SRETRY=0.