Immunohistochemical detection of cell growth fraction in formalin-fixed and paraffin-embedded murine tissue

Monoclonal antibody MIB-1 is a reliable tool for determining proliferating cells in human tissues, but does not react with the homologous mouse antige n and is therefore useless in experimental pathology using mice as model sy stems. Standard method for assessment of cellular proliferation in formalin -fixed, paraffin-embedded murine tissues is immunohistochemical detection o f DNA synthesis using antibodies against exogenously injected 5-bromodeoxyu ridine (BrdU), which is a tedious procedure and not useful for routine inve stigations. We tested monoclonal antibody MIB-5 and monoclonal and polyclon al anti-MCM3 antibodies as immunohistochemical proliferation markers for pa raffin-embedded nonneoplastic and neoplastic tissues of wild-type and trans genic mice, compared to anti-BrdU immunostaining. Percentage of proliferati ng cells was determined with continuously decreasing antibody dilutions. Pe rcentages of MIB-5 and anti-BrdU immunostained cells correlated strongly, a s well as percentage of MIB-5-decorated cells and frequency of mitotic figu res. Anti-MCM3 antibodies labeled significantly higher percentages of cells than anti-BrdU or MIB-5, and showed a linear decrease with increasing anti body dilutions. We conclude that MIB-5 detects reliably the cell growth fra ction in formalin fixed, paraffin-embedded murine tissues, bypassing method ological drawbacks of BrdU. Anti-MCM3 antibodies are less useful for determ ination of proliferating cells although they might detect the fraction of c ells remaining competent for proliferation.