F(ab) secondary antibodies: a general method for double immunolabeling with primary antisera from the same species. Efficiency control by chemiluminescence.

We propose a general solution to the problem of using antibodies originating in the same species for double immunohistochemical labeling. It relies on the use of a two-step protocol in which a secondary polyclonal monovalent F(ab) antibody present in the first step blocks access in the second of the secondary antibody to the primary antibody, which is continuously present from the first step. The monovalence of the F(ab) fragment eliminates the possibility of its linking the primary antibody from the second step. We designed two efficiency tests to explore the limits of the method by the very sensitive chemiluminescent system applied to sections of human pituitary tissue. They confirmed both the validity of the method and the necessity of adapting working conditions to obtain a complete lack of interference.