Secondary Antibody Fragments
Antibody fragments such as Fab (fragment antigen binding) or F(ab’)2 are obtained by cleavage of whole immunoglobulin G (IgG) proteins with papain or pepsin respectively. Since the entire Fc portion of the antibody is absent, these proteins are small and penetrate tissue more easily. Another benefit: less background staining in tissues and cells expressing Fc receptors. Fragmented secondary antibodies are also frequently used to block free binding sites, when several species-identical primary antibodies are used.