Tuberculosis, the 'ticking time bomb' that affects two billion people worldwide and causes an estimated 2 million deaths annually, may have a saviour in vitamin A.
Researchers at University of California Los Angeles (UCLA), investigating the role of nutrients in helping the immune system fight against major infections, found that vitamin A may play an important role combating TB.
The team described the mechanism by which vitamin A and a specific gene assist the immune system by reducing the level of cholesterol in cells infected with TB.
This is important because cholesterol can be used by TB bacteria for nutrition and other needs, the researchers said.
"If we can reduce the amount of cholesterol in a cell infected with tuberculosis, we may be able to aid the immune system in better responding to the infection," said senior author Philip Liu, assistant professor of medicine at UCLA's David Geffen School of Medicine and Orthopaedic Hospital Research Center.
Understanding how nutrients like vitamin A are utilised by our immune system to fight infections may provide new treatment approaches.
To investigate this, the UCLA team first compared its effects on cells to the effects of a similar nutrient, vitamin D, which the group had previously studied.
The researchers thought the two vitamins might use the same mechanism to aid the immune system, but this wasn't the case.
They found that when the vitamins were added to human blood cells infected with tuberculosis, only vitamin A decreased the cells' cholesterol levels.
The researchers also discovered that the action of vitamin A was dependent on the expression of a gene called NPC2.
Further experiments showed that even if an infected blood cell was stimulated with vitamin A, it would not be able to fight the tuberculosis bacteria if the cell couldn't express the NPC2 gene.
"We were very surprised that this particular gene was involved, since it has traditionally been associated with cholesterol transport and not immune defense," noted Elliot Kim, currently a graduate student at UCLA's David Geffen School of Medicine.
"The cells need vitamin A to trigger this defence process and NPC2 to carry it out," added Matthew Wheelwright, a medical and doctoral student at University of Minnesota.
The next stage would focus on better understanding how the immune system takes retinol, the inactive form of vitamin A, and creates all-trans retinoic acid, the form of the nutrient that can activate the infected cells against the tuberculosis bacteria.
This is an early study and that more research needs to be done before recommending vitamin A supplementation to combat tuberculosis or other infections, said the research published in the Journal of Immunology.
