🧬

Immunohistochemistry Overview

Jul 8, 2025

View transcript

Overview

This lecture provides an introduction to immunohistochemistry in pathology, focusing on how different antigens in cells are identified using specific antibodies and chromogenic detection, with practical examples of nuclear, cytoplasmic, and membrane markers.

Immunohistochemistry Basics

  • Immunohistochemistry (IHC) identifies specific antigens in cells using antibodies.
  • The primary antibody binds to the antigen; a secondary antibody binds to the primary.
  • A chromogen attaches to the secondary antibody to produce visible color (often brown or red).
  • Positive staining shows where the antigen is present; unstained areas are negative.

Types of Markers by Location

  • Membrane markers: Stain the cell surface (e.g., CD20 for B lymphocytes).
  • Nuclear markers: Stain only the nucleus (e.g., TTF1 for alveolar cells, p63 and p40 for squamous cells).
  • Cytoplasmic markers: Stain the cytoplasm (e.g., HMB45 for melanomas, napsin A for lung adenocarcinomas).

Key Examples of Markers

  • TTF1: Nuclear marker, positive in lung and thyroid carcinomas.
  • P63/P40: Nuclear squamous cell markers (p40 is more specific).
  • INSM1: Nuclear neuroendocrine marker, more specific than older markers.
  • NUT: Nuclear marker, specific for NUT carcinoma.
  • EBER (SISH/FISH): In situ hybridization marker for Epstein-Barr Virus in the nucleus.
  • PAX8: Nuclear marker for thyroid, kidney, and gynecological carcinomas.
  • GATA3: Nuclear marker for breast and urothelial carcinomas.
  • ERG: Nuclear marker for endothelial cells, better than CD34/CD31.
  • CMV/EBV: Nuclear viral markers in infected cells.
  • ER (Estrogen Receptor): Nuclear marker in breast/endometrial cancers.
  • NKX3.1: Nuclear marker for prostate cancer.
  • SF1/Inhibin: Nuclear/cytoplasmic markers for adrenocortical and sex cord-stromal tumors.
  • STAT6: Nuclear marker specific for solitary fibrous tumor.
  • Pan-Keratin (AE1/AE3, CAM 5.2): Cytoplasmic markers for epithelial tumors.
  • KIT (CD117)/DOG1: Cytoplasmic/membrane markers for GIST.
  • PSA: Cytoplasmic prostate marker.
  • CD Markers (CD20, CD3, CD45, CD68, CD10, CD5, CD138): Generally membrane or cytoplasmic, specific for lymphocytes, plasma cells, etc.
  • CK7/CK20/CK5/6: Cytokeratin markers for epithelial tumors (cytoplasmic/membrane).

Key Terms & Definitions

  • Antigen — a molecule or protein found on/in cells, targeted in IHC.
  • Antibody — a protein that specifically binds to an antigen.
  • Chromogen — a substance that produces color when attached to an antibody complex.
  • Primary/Secondary antibody — first binds antigen, second binds the primary.
  • Nuclear marker — stains the cell nucleus.
  • Cytoplasmic marker — stains the cell cytoplasm.
  • Membrane marker — stains the cell membrane.
  • SISH/FISH — in situ hybridization methods; SISH uses chromogen, FISH uses fluorescent signal.
  • Pankeratin — broad marker for all epithelial cells.
  • CD (Cluster of Differentiation) — standard class of cell surface markers.

Action Items / Next Steps

  • Review examples of major nuclear, cytoplasmic, and membrane markers.
  • Read about the clinical relevance of IHC markers in diagnosis and therapy.
  • Research "Kiel 67" for its pronunciation and origin.

Full transcript