IMMUNOHISTOCHEMICAL LOCALIZATION OF UBIQUITIN CROSS-REACTIVE PROTEIN IN HUMAN TISSUES

Ubiquitin cross-reactive protein (UCRP) is an interferon-inducible ubi quitin homologue which is constitutively present in cells and can be c onjugated to other proteins. Using a characterized polyclonal antiseru m to UCRP, immnunohistochemical localization of UCRP was performed on paraffin-processed normal human tissues and in human tissues known to contain ubiquitinated intracellular inclusions. The antibody to UCRP i mmunostained lymphoid cells, striated and smooth muscle, several epith elia, and neurons. The level of staining varied greatly between tissue s but was in a consistent punctate pattern. Localization to neuromuscu lar junctions and striations is similar to that described for antisera to ubiquitin-protein conjugates. Inclusion bodies characterized by im munoreactivity to anti-ubiquitin were not detected by the antibody to UCRP. Importantly, because UCRP may also be detected by antisera to co njugated ubiquitin, future studies on the distribution of ubiquitin in tissue sections must now take account of possible cross-reactivity wi th UCRP.