Researchers at
the Tulane University have discovered that some monkeys whose
immune systems are depleted by the Simian strain of HIV have a second line of
defense against tuberculosis.
The research led by Deepak
Kaushal, a Professor of Microbiology and Immunology at the Tulane National
Primate Research Center, said it could have significant
impacts on future vaccines for TB.
People co-infected
with Mycobacterium tuberculosis (Mtb) and HIV are up to 20
times more likely than people without HIV to develop active, clinical
tuberculosis over their lifetimes.
HIV targets CD4 T cells
and researchers believe depletion of those cells, the first layer of immune
response, drives up the progression of TB. Currently, most vaccines being
developed for TB only target the CD4 arm of immunity.
Kaushal's research team
exposed macaques to Mtb and simian immunodeficiency virus (SIV) to replicate
human co-infection. They discovered one-third of the animals maintained latent
TB despite complete loss of lung CD4 T cells.
A study of the lung tissue
revealed CD8 cells and B cells both worked to provide immunity against active
TB.
Kaushal says future
vaccines for tuberculosis should try to elicit immune responses from not only
CD4 cells but also CD8 and B cells.
"This monkey model is
the closest we can get to the human environment of these two diseases,"
Kaushal says. "This discovery is important because it lays out the whole
gambit of the different immune functions that are required for an optimum
response."
The research revealed a
sub-population of macaques better able to fight TB and HIV co-infection, and
Kaushal says it can be presumed this sub-population of humans also exists. He
believes the difference is genetic.
Kaushal hopes to continue
the research and move on to the next step of developing a vaccine. "Our
job now is to find out the mechanism of why these differences occurred,"
Kaushal says.
The findings are published
in the Proceedings of the National Academy of Sciences,
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