Epitopes reaction with paratopes

Tissue specimens are fixed in formalin and subsequently embedded in paraffin in the majority of cases. While formalin fixation preserves tissue morphology, it also alters the three-dimensional structure of tissue proteins. This alteration can result in a modification of the antigen s epitopes and/or of its electrostatic charges (EC). The loss of an epitope results in an antigen s inability to react with the paratope of the antibody and can only be corrected by the restoration (retrieval) of the epitope. The reduction of net negative ECs of antigens decreases the avidity of the immune reaction and may be compensated for by prolonging the incubation time with the primary antibody (1) or the use of different antibody diluents (2). 

---