The Zika virus is mostly portrayed in the media as an ultra dangerous infection that causes all sorts of problems in those infected, like microcephaly in babies when pregnant women are exposed to Zika. Portraying this danger is warranted, but the infection can also be surprisingly mild and short-lived. What makes the difference between these two types of infections? From a new study, scientists point at dengue fever.
The dengue virus comes from the same family of viruses as Zika, meaning that the two pathogens share certain genetic and structural qualities. Plus, dengue and Zika occupy many of the same geographic regions. From the La Jolla Institute for Allergy and Immunology, scientists are learning more about how building immunity to the dengue virus can also confer immunity to Zika, and researchers hope to apply the newfound knowledge to vaccine development for both viruses.
In a study with mice, researchers utilized a unique model. Mice were first infected with dengue virus, then were allowed to recover and build immunity. Then, they were infected with Zika. Scientists saw that immunity developed after dengue infection protected mice from a Zika infection. Specifically, they saw reduced burden of Zika virus in blood and tissues compared to mice who were never infected with dengue,
"This may explain why Zika is not passed to the unborn child of every pregnant woman in dengue-endemic countries exposed to virus,” explained lead investigator Sujan Shresta, PhD.
In another experiment, researchers took immune cells called cytotoxic T cells from mice who had built immunity against dengue and injected those cells into “normal” mice, a technique called adoptive T cell transfer. Although the normal mice had never before been exposed to dengue or Zika, their cytotoxic T cells protected them when they were infected with Zika virus for the very first time. Shresta stresses the importance of this finding, which supports the idea that the T cell response is just as important as antibody production in the immune response to Zika virus.
"Approved vaccines for many diseases work by inducing antibody responses,” Shresta said. “But now we are dealing with problematic diseases, like dengue and Zika for which we cannot rely solely on raising antibodies.”
Most existing vaccines primarily focus on an antibody-based approach, which is sometimes sufficient - but not always. Experts like Shresta say that the best way to approach vaccine development is to design a drug that stimulates both antibody production and T cell activation when administered.
“Vaccines targeting either virus could be engineered to induce both T cell and antibody responses effective to protect people in these areas,” Shresta explained. By capitalizing on the “cross-protection” phenomena that exists between dengue and Zika virus as well as the dual approach naturally taken by the immune system - antibody production and a cell-mediated response - vaccine preventing these infections could become drastically more effective.
The present study was published in the journal Nature Communications.