The lymphotropic and myelotropic nature of wild-type measles virus (wt-MV) is well recognized, with dendritic cells and lymphocytes expressing the MV receptor CD150 mediating systemic spread of the virus. Infection of respiratory epithelial cells has long been considered crucial for entry of MV into the body. However, the lack of detectable CD150 on these cells raises the issue of their importance in the pathogenesis of measles. This study utilized a combination of in vitro, ex vivo and in vivo model systems to characterize the susceptibility of epithelial cells to wt-MV of proven pathogenicity. Low numbers of MV-infected epithelial cells in close proximity to underlying infected lymphocytes or myeloid cells suggested infection via the basolateral side of the epithelium in the macaque model. In primary cultures of human bronchial epithelial cells, foci of MV-infected cells were only observed following infection via the basolateral cell surface. The extent of infection in primary cells was enhanced both in vitro and in ex vivo cornea rim tissue by disrupting the integrity of the cells prior to the application of virus. This demonstrated that, whilst epithelial cells may not be the primary target cells for wt-MV, areas of epithelium in which tight junctions are disrupted can become infected using high m.o.i. The low numbers of MV-infected epithelial cells observed in vivo in conjunction with the absence of infectious virus release from infected primary cell cultures suggest that epithelial cells have a peripheral role in MV transmission.
INTRODUCTIONMeasles is a severe disease contributing to significant morbidity and mortality rates in many parts of the developing world (Grais et al., 2007). It is also of growing concern in some areas of the developed world where the vaccination rate has fallen below the level required to prevent periodic outbreaks of measles (Choi et al., 2008). The disease is characterized by fever and a maculopapular rash, often in conjunction with cough, coryza and/or conjunctivitis, and a generalized immunosuppression. The causative agent, wild-type measles virus (wt-MV) is spread by aerosolized droplets or direct contact (Griffin, 2007). The highly infectious nature of MV not only suggests a very efficient route of entry into the body but also an effective means of dissemination to susceptible individuals following systemic spread of the virus within the body.The tropism of MV in vivo is determined mainly by the distribution of CD150, also known as signalling lymphocyte activation molecule (SLAM), which is the primary cellular receptor for wild-type strains of the virus. The molecule is widely expressed in lymphoid tissues on subsets of B and T lymphocytes, thymocytes, macrophages and dendritic cells (DCs) (Kruse et al., 2001;McQuaid & Cosby, 2002). This is reflected by analysis of MV-infected cell types present at different stages of the disease, which shows that, in all tissues involved, the majority of infected cells are of a lymphoid origin (Hall et al., 1971; Moench et al., 1988). Ano...