The impact of murine cytomegalovirus (mCMV) route and age at infection upon virus spread, immune responses and the establishment of latency

Cytomegalovirus (CMV) is a ubiquitous human virus, which establishes a characteristic lifetime infection in its host. Murine CMV (mCMV) is a widely-used infection model that has been employed to investigate the nature and extent of CMVs contribution to inflammatory, immunological, and health disturbances in humans. In an effort to assess the role of route and age in modeling hCMV infection in mice, we have performed a comparative analysis of two common experimental modes of infection (intraperitoneal and intranasal) at two different clinically relevant ages (4 weeks, or prepubescent childhood equivalent, and 12 weeks, or young postpubescent adult). We found that while both routes of infection led to similar early viral loads, differential activation of several parameters of innate immune function were observed. In particular, younger, prepubescent mice exhibited the strongest NK activation in the blood in response to i.p. infection, with this trend holding true in NK cells expressing the mCMV-specific receptor Ly49H. Moreover, i.p. infected animals accumulated a larger amount of anti-mCMV IgG and experienced a greater expansion of both acute and latent phase CD8+ T cells. This was especially true for young postpubescent mice, further illustrating a distinction in the bloodborne immune response across not only infection routes, but also ages. These results may be important in the understanding of how a more physiologically applicable model of CMV influences immunity, inflammation, and health over the lifespan.