Blocking in immunohistochemistry represents an important step in order to obtain clear and specific signal and prevent non-specific antibody binding. In general, sera from the species in which the secondary antibody has been raised, is used. Another option is to use serum albumin as a more affordable alternative. Nowadays a plethora of commercial blocking solutions and animal-free blockers are also available.
Sera from various species, Mouse on Mouse (M.O.M.™) kit and blocking reagent, Animal Free Blocker™