Effect of tissue fixation on anti-bromodeoxyuridine immunohistochemistry

We investigated the influence of various fixatives on monoclonal anti-BrdUrd antibody binding of BrdUrd-substituted DNA in tissue sections of routinely processed mouse small intestine after in vivo administration of BrdUrd. For denaturing fixatives such as ethanol or Carnoy's fluid, a standard denaturation protocol showed specific crypt cell labeling. With cross-linking agents such as formalin and glutaraldehyde, a remarkable increase in staining intensity was obtained after tissue digestion with pepsin before acid denaturation. The optimal pepsin concentration was determined for maximal immunoreactivity combined with acceptable morphology.