Blocking for Nonspecific Antibody Binding

Fc receptors in tissue bind the Fc end of the primary antibody and lead to incorrect labeling (Fig. 5.2). Fc receptors are found on macrophages and other immune cells, and can bind any antibody in the immunocytochemistry procedure. The primary antibody would most likely bind open Fc receptors as the first antibody incubation. This problem occurs only in areas where there are macrophages, such as injury and inflammation sites. Unless cell cultures include macrophage or natural killer cell lines, Fc receptor binding does not occur in cultures. 

For example, when using a mouse monoclonal antibody against tubulin in rabbit tissue with a secondary goat anti-mouse 488 fluorophore, the blocking step would 

Fab fragment (black) from antibody (outline) to species of tissue 

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