According to researchers at the University of Pittsburgh School of Medicine and Texas A&M University, lung lesions infected with tuberculosis (TB) are surprisingly variable and independent of each other, despite whether the patient has clinically active or latent disease.
It is reported that over 30 percent of the world’s population is infected with Mycobacterium tuberculosis. Five to 10 percent of the people who are infected develop active contagious disease with symptoms like coughing, chest pain, night sweats and weight loss. Most individuals are asymptomatic or latent with infections that are not contagious that become active years later.
When an individual becomes infected, the immune system walls off the bacteria. These walled off lesions are known as granulomas. According to JoAnne Flynn, Ph.D., professor of microbiology and molecular genetics, Pitt School of Medicine and co-senior investigator, “It’s long been thought that the patient with a weakened immune system or some other immune vulnerability was more likely to develop active disease. But to our surprise, our study showed that every infected individual has a collection of granulomas, some containing live bacteria and some that are sterile because the immune system has killed all the bacteria. So in this sense, there’s no such thing as a latent or active granuloma.”
The researchers infected monkeys with TB and then tracked the granulomas that developed. They observed that each granuloma begins with one bacterium. The bacterium replicates for about 4 weeks before the body adapts with an immune response to kill them off. According to Flynn, “This response was sufficient to kill all the bacteria and sterilize some granulomas, but bacteria persisted in others and spread to create new granulomas. You need only one granuloma to ‘go bad’ in order to get active TB.”
The researchers are uncertain as to why there were different responses in different lesions. Hopefully when they do, they’ll be able to develop a vaccine to prevent TB.