What's the difference between immunohistochemical staining and flow cytometry?

Question

they both involve attaching a fluorescent label with antigens attaching to antibodies on the surface of the cells...

Answer 1

They're very different actually.

Immunohistochemistry is imaging of tissue rather than cells (the same technique applied to cells is immunocytochemistry). IHC also doesn't necessarily involve fluorescent antibodies. You can do it with an antibody tagged with pretty much anything visible - so for example antibodies are often tagged with horse radish peroxidase, and the enzyme is used to cleave a colorigenic substrate so you can then see the tissue. However, as you say, fluorescent antibodies are becoming increasingly popular in both immunohistochemistry and immunocytochemistry.

Flow cytometry is rather different. Rather than using fixed cells or tissue on a coverslip you have fluorescent antibody labelled cells in a suspension which you then feed through a flow cytometer. If you label these cells with several different fluorescent antibodies the flow cytometer can then split the cells by which antibody they are tagged to, as well as other parameters such as size.

In the process of separating the cells into different groups the flow cytometer counts the number of cells in each group (hence the term "cytometer", meaning cell counter).

Bit long, but hopefully that clarifies things for you.

Answer 2

Immunohistochemical (IHC) staining is a technique for detecting certain proteins, usually antibodies in a given sample of tissue (often used when preparing slides with the sample embedded in parafin). It is possible to use IHC to determine the concentration of certain antiboy proteins but it may not tell you specifics about which ones unless you know what you are testing for and use certain additional knowledge in your analysis, while flow cytometry is a method of complex analysis and manipulation that involves particles which are suspended in a fluid stream medium. Flow cytometry can be used to determine very precise details about composition and a host of other characteristics for each particle of the sample which may be important in certain types of DNA testing.They are both useful tools to a biologist or a medical researcher with different kinds of results and which one you choose to use depends on what you want to know.