Retroviruses tend to be of great interest to the general public, because of all the media attention given to widely problematic ones, such as the Human Immunodeficiency Virus (HIV). Before effective vaccines against retroviruses like HIV can be produced, a basic understanding of how the immune system responds to them is imperative. When a retrovirus enters the human body, many are known to overcome the immune system, and possibly inhabit the host long-term. However, some animals have developed very efficient immune responses, which allow them to essentially evade or kill the virus. Scientists can study animals with this ability, like mice, to better understand the specificities of their immune systems that facilitate its advantage over the retrovirus, in hopes of relating their findings back to humans.
The first line of defense in the immune response is the innate immune system. The innate immune system is often thought of as “natural,” and provides non-specific protection against foreign invaders (1). Innate defenses are found all over the body, and include physical barriers like skin and mucus. Additionally, the innate immune system responds to pathogens in a generic way and has multiple mechanisms for killing and removing invaders. Most times, the innate defenses are successful. However, if the innate immune system is unsuccessful, it is responsible for triggering the secondary reaction of the adaptive immune system. The adaptive immune response is a specific response to a particular pathogen (foreign invader) and is usually only triggered by those entities that successfully overcome the innate immune response (1). Previous research has shown that in some strains of mice, the innate immune system senses the virus and triggers the appropriate adaptive immune response specific to the virus (2). So although the adaptive immune response is responsible for controlling retroviruses in mice, the first, critical innate virus-sensing step is still not confirmed.
Viruses are unique because they are recognized by endocytic pattern recognition receptors (PRR) on host leukocytes (white blood cells) that detect replication intermediates (nucleic acids) produced by the virus (2). However, it is unknown whether these viral sensors play a vital role in virus sensing in vivo, which is why animal models are very helpful. A recent paper by Kane et al. (2011) is therefore broadly asking whether retroviral replication intermediates are recognized by the innate immune system and further, if they are critical components for the adaptive immune response.
