A tiny invader, perhaps a virus or a microbe, enters the body, and our ancient immune system responds. But how does it know what kind of invader has landed? And once it knows, how does it decide what kind of immune response it should launch?
Itâ€™s the innate immune systemâ€™s job to recognize the first signs of infectionâ€”that is, the moment a pathogen enters the body. â€œIn a sense they act as smoke detectors if you will,â€ says Pulendran. â€œLittle alarms.â€
And itâ€™s the adaptive immune system that identifies what kind of pathogen has crossed the immune systemâ€™s threshold. In other words, the immune system can recognize nearly any antigen in the universe. Whatâ€™s more, the adaptive immune system has a long memory.
â€œThereâ€™s immune memory,â€ says Pulendran. â€œAnd immune memory is the essence of vaccination. A few decades down the line if there are any re-exposures to that same virus, the immune system will respond much more quickly and rapidly to control the virus.â€ Much like the immune system does after a vaccination.
Pulendran and his colleagues are now trying to understand how vaccines, especially highly successful ones, work and what makes them effective. â€œAlmost all vaccines have been made empirically. In other words, we donâ€™t really know how these vaccines work. We donâ€™t know the mechanisms by which they work. Whatâ€™s happened in the last five years or so as weâ€™ve begun to look at the highly successful vaccines, for example, the yellow fever vaccine, which is a live virus.â€
What researchers have found is that the strength of the yellow fever vaccine is attributable to its ability to identify not only individual pathogens but unique components of those pathogens and then act on them.
â€œSo, weâ€™re getting closer to reverse engineering some of our best vaccines,â€ says Pulendran. â€œUnderstanding the rules of immunology by which they work. So, armed with this insight we hope to be calm and more rational in designing new vaccines against HIV, malaria, tuberculosis and other emerging infections.â€
To listen to Pulendranâ€™s own words about the immune system, access Emoryâ€™s new Sound Science podcast.