Macrophages and Dendritic Cells Are the Predominant Cells Infected in Measles in Humans

Characterization of human measles cases is essential in order to better assess the data generated in model systems of morbillivirus infection. To this end, we collected formalin-fixed tissue samples from 23 natural measles cases from different areas in the world and different phases of disease ranging from prodromal and acute measles to a persistent infection in an immunocompromised subject. We show that the vast majority of measles virus (MV)-infected cells in epithelia were intraepithelial immune cells that were, in most cases, positive for the CD11c myeloid cell marker. Small numbers of measles virus-infected cytokeratin-positive epithelial cells were also detected in bronchial and appendix epithelia. Dissolution and disruption of uninfected and MV-infected alveolar and bronchial epithelia were prominent features of the measles cases, especially in the established and late phases of the disease. In some instances, this was associated with the formation of MV-infected multinucleated giant cells which expressed CD11c and/or macrophage cell marker 68, a pathological feature also prominently observed in closely associated mucosa-associated lymphoid tissue. Collectively, these data show that resident and inflammatory infiltrating immune cells alter the architecture of respiratory tract epithelia and highlight the necessity for additional research into the function(s) and expression of nectin-4 in human tissues. We have brought together a unique collection of 23 human cases of measles infection and studied the types of cells that are infected. This work has not been done with modern technologies such as double labeling with antibodies and confocal microscopy in human cases primarily due to the fact that it is difficult to obtain the material because, fortunately, measles is fatal in only a very small fraction of infected patients. During the past decades, the receptors for measles virus have been elucidated and monkey models have been developed. We found that, in most cases, independently of whether the tissues were obtained early or later in the infection, the primary cell types that were infected were those of the immune system such as lymphocytes, macrophages, and dendritic cells. A very small number of epithelial cells were also found to be infected.