Phosphohistone H3 (pHH3) is a recently described marker specific for cells undergoing mitosis. Serine 10 of Histone H3 is phosphorylated in association with mitotic chromatin condensation in late G2 and M phase of the cell cycle and thus, pHH3 can distinguish mitosis from apoptotic nuclei (1). Microscopic evaluation of mitotic figures by hematoxylin and eosin (H&E) staining is a routine procedure in the assessment of the prognostic grade of tumors (2,3). The immunohistochemical (IHC) staining of pHH3 (Ser10) has been reported to be comparable to mitotic figure staining in the H&E section (4-6). However, in some cases, H&E staining may misclassify mitotic cells as apoptotic bodies or piknotic nuclei, resulting in an underestimation of the mitotic index (MI). IHC with pHH3 may provide a more accurate assessment of all mitotic cells, as well as cells in which Histone H3 has been phosphorylated immediately prior to entering prophase (7). Prognostic significance of the mitotic index using an anti-pHH3 antibody has been reported to be of great value in breast cancer, melanoma and meningiomas (8,9).
A rabbit monoclonal (RM) antibody targeting phosphorylated Serine 10 of pHH3, clone [BC37], has been developed and characterized by Western blot, ELISA, and IHC. In tonsil and melanoma, pHH3 (RM) displays stronger staining intensity in mitotic figures compared to the polyclonal pHH3. Additionally, pHH3 (RM) does not exhibit granular staining in interphase nuclei, unlike the polyclonal pHH3 (Figure 1A, 1B). pHH3 (RM) may offer other advantages common to rabbit monoclonal antibodies, including a specific epitope and lot-to-lot consistency.