Immunohistochemistry
A section of tissue is taken as it would for Histology (see prev post)
The section is then treated with an antibody that recognises the marker we’re looking for. This is referred to as the primary antibody.
The primary antibody is then recognised by a secondary antibody that is linked to an enzyme, or several copies of the enzymes (conjugates).
Finally, the section is treated with a chromogen, a reagent that is acted upon by the enzyme, to deposit an insoluble coloured compound onto the cell, where the original primary antibody had bound.
A molecule that binds to, and is recognised by, an antibody, is called an antigen,
In histology, antigens = markers, since they act as ways of recognising a particular cell.
Many markers are designated by a CD number.
EG different classes of lymphocyte appear virtually identical in size and shape (morphology), but they can be distinguished according to their surface markers.
All T lymphocytes express CD3,
Helper T cells and cytotoxic T cells express CD4 and CD8, respectively.
Therefore, a T cell lymphoma can be tracked in different tissues using these markers.
Double immunolabelling of an islet of Langerhans in the pancreas identifies Insulin-producing cells (blue) and glucagon-producing cells (brown)
Another use for IHC is in guiding treatment.
For example, many breast cancers require oestrogen to divide, but a drug called tamoxifen can bind to the oestrogen receptor on the cancerous cells, blocking this proliferative effect.
