Occult cytomegalovirus in vivarium-housed mice may influence transplant allograft acceptance

Abstract

We have recently shown that latent murine cytomegalovirus (MCMV) can influence murine transplant allograft acceptance. During these studies we became aware that vivarium-housed control mice can acquire occult MCMV infection. The purpose of this investigation was to confirm occult MCMV transmission and determine the timing, vehicle, and possible consequences of transmission. Mice arriving from a commercial vendor were negative for MCMV both by commercial serologic testing and by our nested PCR. Mice housed in our vivarium became positive for MCMV DNA 30-60 days after arrival, but remained negative for MCMV by commercial serologic testing. To confirm MCMV we sequenced PCR products for several genes and showed >99% homology to MCMV. Further sequence analyses show that the occult MCMV is similar to a laboratory strain of MCMV, but the vehicle of transmission remains unclear. Control tissues from historical experiments with unexplained graft losses were evaluated for occult MCMV, and mice with unexplained allograft losses showed significantly higher incidence of occult MCMV than did allograft acceptors. Deliberate infection with very low titer MCMV confirmed that viral transmission can occur without measurable virus specific antibody or T-cell responses. These data suggest that vivarium-housed mice can develop occult MCMV that is missed by currently available commercial serologic testing, and that these infections may influence transplant allograft acceptance.

Cytomegalovirus Reinfections Stimulate CD8 T-Memory Inflation

“…The concept that CD8 memory inflation can be determined at the time of primary infection and in fact be predicated by the infecting viral load was suggested to us by our earlier published work [24]. This finding has been recently corroborated by Redeker et al who performed very detailed immunophenotyping using a different C57BL6 model [27].…”

“…Recent work has suggested that lower doses of mCMV during primary infection influence the absolute magnitude of the CD8 T-cell response [24, 27], but not the early expansion/contraction of mCMV-specific T-cells nor early development of T-memory [15]. What remains unclear is whether low titer viral infections will stimulate long term T-cell inflation similar to high titer infection.…”

“…We have previously observed that vivarium housed mice can develop very low level mCMV infections without measurable antibody responses [24]. Similarly, there are reports of humans who are hCMV DNA positive by PCR assay but have no detectable hCMV specific antibody [33, 34].…”

“…This hypothesis is supported by work from several investigators that suggests that mice infected with very low doses of CMV develop CD8 T-memory responses but not classic memory inflation [15, 24–27]. Complicating matters further, recent human data show that reinfection can occur despite pre-existing “immunity” [28–31], and the role that reinfection plays in memory inflation remains undefined.…”

Cytomegalovirus reactivation in critically ill immunocompetent hosts: A decade of progress and remaining challenges

“…Curiously, unlike mice undergoing high titer infections, not all humans develop T-memory inflation (Gillespie et al, 2000; Sylwester et al, 2005; Vescovini et al, 2007). We have recently shown that the development of such inflationary memory may depend upon the conditions of the original infection (Thomas et al, 2010), and we are currently attempting to determine whether repeated reactivation episodes can cause MCMV-specific memory inflation as has been suggested to occur in humans.…”