Our mAbs clones CROMA 7, m55.01 and m55.02 recognize MCMV protein m55, also known as gB. gB is a major envelope transmembrane glycoprotein, part of the protein machinery promoting the fusion process involved in virus entry. It is encoded by a gene transcribed in late phase of infection (after 16 h p.i.). gB is highly conserved among different herpesviruses and is a major target of virus-neutralizing antibody responses in CMV-infected animals and humans (Britt WY et al, J Virol, 1990). In addition, HCMV gB is also involved in cell adhesion and signaling capabilities (Boyle, KA et al, J Virol, 1998; Boyle, ka et al, Mol Cell Biol. 1999. gB is present in several protein isoforms of different molecular masses, with the 130kDa form being gB precursor protein (Rapp, M et al, J Virol, 1992). It has been proposed for HCMV that a cellular protease cleaves precursor gB resulting in additional protein forms of lower molecular mass (Spaete RR et al, Virology 1988). This can be also observed by staining MCMV-infected cells with our M55.01 clone in western blot since this clone recognizes all forms. On the other hand, cloneM55.02 recognizes only the form of the highest molecular weight (130kDa). Additional tested applicatons are as follows: Croma 7 (described in the Journal of Infectious Diseases (2003) 187 (6): 988-999) works in IHC; M55.01 and M55.02 work in flow cytometry; M55.01 and Croma7 work in IF. Each LOT is validated for western blot on MCMV infected cell lysates.