Murine cytomegalovirus m119-118 encodes a new viral Fc receptor antagonizing host Fc receptor activation

Mice are susceptible to a virus called murine cytomegalovirus (MCMV) which employs various tactics to avoid the body's immune system. One of these tactics involves proteins called viral Fc receptors (vFcRs) that bind to the Fc region of antibodies, interfering with their ability to carry out their protective roles. In humans, there are four types of these vFcRs, but in mice, only one such receptor, called fcr-1, has been found.

A recent investigation into the MCMV genomes of three strains - v70, K181+, and K181Perth - identified a mutation in the m119-118 gene, which led to the discovery of a second vFcR named fcr-2. The structure of fcr-2 is similar to a counterpart in human CMV called UL119-118/gp68, and it also binds to the Fc part of mouse IgG antibodies.

When both vFcR genes were removed from the MCMV genome, the virus was unable to bind effectively to the antibodies on the surface of infected cells. This was confirmed by experiments with viral mutants that showed both proteins work together to block the activation of the host's Fc receptors. While a MCMV lacking the fcr-1 receptor showed only a slight reduction in its ability to infect mice, a double mutant lacking both fcr-1 and fcr-2 showed significantly lower levels of the virus in various organs.

This suggests that these two vFcRs play a crucial role in MCMV's ability to spread and cause disease in mice.