October 1, 2018

Cytomegalovirus, or CMV, is a common virus found in almost every person on the planet. For most of them, it causes no harm and leads to no symptoms. But for newborn babies and people with compromised immune systems, it can lead to birth defects, serious illness and even death.

Now, researchers associated with the California National Primate Research Center (CNPRC) at the University of California, Davis have discovered that low levels of CMV changed microbe and immune cell populations and response to the flu vaccine in rhesus macaques. CMV infection generally increased immune activity but also diminished antibodies responding to influenza vaccination. The study also found that low levels of CMV make the body susceptible to changes in environmental conditions that could accentuate their impact.

“Subclinical CMV infection alters the immune system and the gut microbiota in the host and that impacts how we respond to vaccines, environmental stimuli and pathogens,” said Satya Dandekar, who chairs the Department of Medical Microbiology and Immunology at UC Davis and is a core scientist in the infectious diseases unit at CNPRC at UC Davis. “This study highlights the role of these silent, latent viral infections that are totally asymptomatic.”

The researchers believe that these low-level CMV infections may be one reason for the variation in response to vaccines across large populations. One possibility is that the immune system’s constant effort to control CMV might be diverting resources that it might direct to other threats.

The next step in the process will be testing other vaccines in CMV-infected animals and generally working to better understand how subclinical viruses affect the immune system.

“This highlights the impact silent viruses have to influence how the host responds to vaccines,” said Dandekar. “Can we somehow use this information to optimize our immune system? That’s the direction we would like to go to see how we can inhibit CMV to see if we can enhance the vaccine response.”

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