AD Histopathology Flashcards
Learning Objectives - Identify histopathology techniques used to identify hallmarks of AD - Identify and explain different stains used in various histopathology techniques: Congo Red, Thioflavin S, Silver Staining, IHC
Describe the relationship between B cells and antibodies.
- Each B cells expresses a single type of antibody on its surface
- When an antigen binds to the unique antigen-binding site on the antibody, the B cells proliferates and differentiates in an antibody secreting effect B cells
- Some of these B cells become plasma cells (secrete lots of antibodies into the bloodstream)
How is tissue processed for staining techniques like IHC?
- Spleens are fixed in a chemical to preserve tissue structure and proteins
- Samples are embedded in paraffin to allow for thin sectioning for microscopic analysis
- Tissue is sectioned where thin slices are cut
Describe the purpose of the primary antibody for IHC.
- Used to directly bind to target protein
- Specific to the protein so only the protein you care about is detected
What is the purpose of a secondary antibody for IHC?
- Recognizes and binds to the primary antibody
- Used to amplify the signal (lots can bind to primary antibody) to increase the likelihood that it’s detected
- Sometimes labelled with enzymes for better visualization
How is the primary antibody chosen for IHC?
- Antibodies are raised against specific protein sequences or structures
- Ex. For AD research, an anti-amyloid-beta antibody is used to detect amyloid plaques
What is a monoclonal antibody?
- Highly specific
- Recognizes only one epitope (specific part of a molecule that an antibody binds to)
What is a polyclonal antibody?
- Recognizing multiple epitopes on the same protein
What are chromogenic substrates in IHC?
- Compounds that produce a color change when reacting with an enzyme conjugated to the secondary antibody (color)
- Ex. DAB stains the tissue brown
- Helps visualize the presence and location of target proteins in tissues
- Insoluble, colored precipitate forms at the site of target protein
What is the counterstain in IHC?
- Counterstain tissue in order to identify other cellular structure not targeted by the primary antibody
- Provides background contrast
- Ex. DAPI - shows cell nuclei
What does the Congo Red Stain bind to?
Binds to beta-pleated sheet structures in amyloid deposits
What does a Congo Red stain recognize?
- Amyloid deposits
- Particularly in Alzheimer’s plaques
What color does a Congo Red stain appear under polarized light and normal light conditions?
- Polarized: bright apple green
- Normal: orange-red, slightly pink
What is Thioflavin S and what does it bind to?
- A fluorescent dye
- Binds to amyloid fibrils and misfolded proteins
What does a Thio. stain recognize?
Amyloid plaques and NFTs in AD
How do plaques appear under Thioflavin S staining?
- Bright green
- Circular in shape
- Depending on maturity level, some are more dense at core with a less dense halo surrounding it
What is silver staining and what does it bind to?
- A metal-based staining technique using silver impregnation
- Binds to NFTS (primary), AB plaques, and neuronal cell bodies
What does silver staining recongnize?
- Neuronal pathology (ex. NFTs)
How do NFTs and plaques show up via silver staining?
- Tau filaments: black, dark brown
- Tangles can appear in cell bodies of neurons
- AB plaques: dense, irregular areas, dark brown, lighter than tau
What is IHC and what does it bind to?
- A highly specific staining technique using antibodies to detect proteins
- Binds to specific proteins using antigen-antibody interactions
What does IHC recognize?
Disease-specific protein markers
Describe Parkinson’s disease (PD).
- Affects movement and cognition
- Progress loss of dopaminergic neurons in the SNpc part of brain
- Largely driven by protein dysfunction –> leads to cell damage and death
What is the pathology of alpha-synuclein in PD?
- Misfolds and clumps together
- Forms toxic structures called Lewy bodies
- Normally, it help with movement of molecules in brain cells
Explain the cascade effect of misfolded alpha-synuclein in PD.
- Misfolding disrupts synaptic vesicles (sacs that store and release dopamine)
- Less dopamine is available
- Leads to movement issues
- More neurons die, dropping dopamine levels more
