JAN 17, 2017 10:46 AM PST

Persistent Infections Promote Long-Term Immunity

WRITTEN BY: Kara Marker

Both natural and artificial bestowal of long-term immunity comes with risks. The same pathogen or vaccine that is conferring resistance protects an individual from disease and simultaneously poses a risk for disease later in life when an individual is vulnerable due to age, illness, or both.

The parasite (shown in green) is constantly multiplying and being killed by immune cells (pink and blue), keeping the immune system alert. Credit: M. Mandell, S. Beverly

Researchers from the Washington University School of Medicine studied the balance of risks and benefits that come with persistent infections, looking for ways to improve vaccine development and treatment designs for diseases like leishmaniasis, where initial exposure to the parasite prevents subsequent infections later in life.
 
Leishmaniasis is a parasitic disease found in individuals who live in the tropics, subtropics, and southern Europe; it is classified as a “Neglected Tropical Disease.” The disease is spread via the bite of a phlebotomine sand fly, which harbors the pathogen responsible for the infection. The parasite can cause either skin sores - “cutaneous leishmaniasis” or an infection of internal organs like the spleen, liver, and bone marrow - “visceral leishmaniasis.”

Washington University scientists studied leishmaniasis parasites in mice, designing fluorescent markers that could distinguish different types of cells. From the markers, they found that a large majority of the parasites that persisted after an infection seemingly cleared shacked up inside of the very immune cells capable of killing them. But other than that strange finding, the parasites appeared to be normal in shape and size.

Another bizarre discovery was that although the parasites were continuing to multiply, the total number of living parasites stayed the same over time. "We were unable to show directly that the parasites were being killed,” explained senior author of the study Stephen Beverley, PhD. “But some of them must have been dying because the numbers weren't going up."

Beverly and the rest of the research time believe that this continuous multiplication is the process responsible for long-term immunity and protecting people with infections like leishmaniasis from getting the same infection twice.

"It seems that our immunologic memory needs reminding sometimes," said first author Michael Mandell, PhD. "As the persistent parasites replicate and get killed, they are continually stimulating the immune system, keeping it primed and ready for any new encounters with the parasite."

"People had been thinking of the role of the immune system in persistent infection in terms of mowing down any pathogens that reactivate in order to protect the body from disease," Beverly said. "What was often overlooked was that in the process of doing this, the immune system is constantly being stimulated, which potentially promotes protection against future illness."

A sand fly (left) and Leishmania parasites in culture (right). Source: Public Health Image Library


The next step for Beverly and his team might be to research developing a vaccine that mimics the pattern of “reminding” to keep the body immune to a particular disease, even if it poses a risk of infection to the individual receiving the vaccine. “For some of these organisms, solid, long-term protection may come at the price of persistent infection,” Beverly explained.

This approach could be applicable to many other diseases other than leishmaniasis that also cause persistent infections: tuberculosis bacteria, herpes and chickenpox viruses. Leishmaniasis alone causes tens of thousands of deaths every year.

Beverly’s study was recently published in the journal Proceedings of the National Academy of Sciences.

Sources: CDC, Washington University School of Medicine

About the Author
I am a scientific journalist and enthusiast, especially in the realm of biomedicine. I am passionate about conveying the truth in scientific phenomena and subsequently improving health and public awareness. Sometimes scientific research needs a translator to effectively communicate the scientific jargon present in significant findings. I plan to be that translating communicator, and I hope to decrease the spread of misrepresented scientific phenomena! Check out my science blog: ScienceKara.com.
You May Also Like
SEP 29, 2022
Neuroscience
How the Circadian Clock Promotes Injury Recovery
SEP 29, 2022
How the Circadian Clock Promotes Injury Recovery
A new study conducted by a research team at Children's National Hospital examined how the body’s internal cloc ...
OCT 28, 2022
Coronavirus
The New GenElute™-E Viral RNA/DNA Kit
OCT 28, 2022
The New GenElute™-E Viral RNA/DNA Kit
Three Advantages: Reduction in plastic use Time savings Better results Nucleic acids play an essential role in the funct ...
NOV 07, 2022
Immunology
A High-Fat Diet May Alter Immunity
NOV 07, 2022
A High-Fat Diet May Alter Immunity
The physiological impact of various diets has been hotly debated for years. Scientists have now used a mouse model to sh ...
NOV 21, 2022
Immunology
Unusual, Ultrapotent Antibody Against Zika is Discovered
NOV 21, 2022
Unusual, Ultrapotent Antibody Against Zika is Discovered
Zika virus is transmitted by the Aedes aegypti mosquito and can cause a mild illness in otherwise healthy adults. But wh ...
NOV 30, 2022
Immunology
Rogue, Cancer-Linked Immune Cells Found to Drive Autoimmune Disorders
NOV 30, 2022
Rogue, Cancer-Linked Immune Cells Found to Drive Autoimmune Disorders
Leukemia patients are more likely to get autoimmune disorders like aplastic anemia or rheumatoid arthritis than unaffect ...
DEC 07, 2022
Immunology
A Mystery Solved - Why Colds & Flu Are More Common in Winter
DEC 07, 2022
A Mystery Solved - Why Colds & Flu Are More Common in Winter
Most people would agree that colds and especially flu infections are far more common in winter. While we know that some ...
Loading Comments...