An immune cell type thought to be restricted to the general, first response to pathogenic invaders may actually have some memory capabilities. Even more, this cell type may hold the key to new prevention strategies for hepatitis B infection.
Current vaccination against hepatitis B virus (HBV) utilizes a classic approach: protection through immunological memory by introducing the virus in a benign setting so the immune system can build up immunity if and when the “real” virus shows up. This strategy is based on science that exhibits B cells and T cells controlling the bulk of immunological memory.
However, a new study indicates natural killer (NK) cells may also be involved in immunological memory, at least when it comes to HBV. NK cells are typically associated with the innate immune response, an unspecific, first response to infections and cancer, as opposed to the adaptive immune response, which is a specific, targeted response associated with B cells, T cells, and antibodies responding to pathogen-specific antigens.
The novel concept of NK cells with memory capabilities was first introduced in mouse models, and researchers from the current study took it one step further to confirm whether the same relationship between NK cells and immunological memory held true in human viral infections.
Researchers analyzed NK cells in humans who had either been infected with HBV or vaccinated for protection from HBV, comparing samples from both groups to samples from people with zero exposure of any kind to HBV. Ultimately, this comparison led to the discovery of memory NK cells as part of the adaptive immune response to HBV exposure.
"Previously, we thought that the NK immune response was part of our 'innate' immune system,” explained study leader Professor Golo Ahlenstiel. “We have now confirmed that NK cells in humans can acquire an immunological 'memory', and specifically target HBV-infected cells in subsequent infections."
HBV infections usually target the liver, and in worst case scenarios, HBV infection can lead to live cancer, liver cirrhosis, and liver failure. Transmission often occurs between mother and child during birth, but it can also occur through other types of contact with infected blood or other body fluids. Many people exposed to HBV ultimately develop chronic infections that need addressed on a long-term basis.
A small but significant percentage of people will not respond to vaccination, leaving them vulnerable to HBV infection without an effective protective solution. The World Health Organization (WHO) estimated that HBV resulted in 887,000 deaths in 2015. Discovering the existence and role of memory NK cells may offer a new avenue for unique preventative therapies for HBV.
Sources: Westmead Institute for Medical Research, Hepatology, World Health Organization
