What are the general blocking procedures for immunohistochemistry (IHC)?

In immunohistochemistry (IHC), one or more blocking steps are used to prevent nonspecific binding of antibodies and reduce background staining. The blocking step is typically performed after completing all other sample preparation steps but before incubating the sample with the primary antibody. 

The general blocking procedure involves incubating the IHC sample with the appropriate blocking buffer. The IHC sample must be fixed, embedded, mounted, sectioned, deparaffinized, and unmasked before incubation. 

After incubation, the sample is left for 30 minutes to overnight, either at room temperature or 4°C. The timing and temperature depend on the optimized protocol specific to each antibody and target antigen. 

The blocking step is followed by sufficient washing to remove excess protein that could interfere with the detection of the target antigen. Some researchers omit the washing step after blocking.