Washington, Mar 2 : Scientists have found that Vitamin A plays a major role in the process whereby dendritic cells signal the white blood cells about any intrusion in the body.

Researchers at the Emory Vaccine Center and Yerkes National Primate Research Center have discovered that dendritic cells can respond to a compound called zymosan, a component of yeast cell walls, through two different receptors by sending out both stimulatory and calming messages at once.

The scientists say that their findings may prove useful for designing vaccines against many infectious agents, as the calming receptor is known to respond to bacteria and viruses as well as yeast.

Besides, silencing the calming receptor''s messages might boost the immune system''s ability to fight a chronic infection.

It was found that the calming receptor, known as TLR2 (Toll-like receptor 2), uses vitamin A to transmit its signals.

This may explain the connection between vitamin A deficiency and autoimmune diseases-Vitamin A deficiency has been linked to diseases like rheumatoid arthritis, lupus and type I diabetes.

Senior author Dr. Bali Pulendran, professor of pathology and laboratory medicine at Emory University School of Medicine, said that the "two signals at once" feature of the immune system could be viewed as the result of an evolutionary tug of war.

"The immune system has to provide a defense against infection, while avoiding the destruction of too much of the body along the way. At the same time, pathogens have evolved strategies to manipulate the immune system for their own purposes," Nature magazine quoted him as saying.

The researchers analysed which genes are turned on in dendritic cells by zymosan in cell culture.

To their surprise, it was found that both zymosan and live Candida albicans, which causes yeast infections, turned on genes involved in converting vitamin A to its active form, retinoic acid.

"Others have seen that these genes are turned on constitutively in the gut, but seeing how they can be induced elsewhere is new," said Pulendran.

It was found that dendritic cells use retinoic acid along with other chemical messengers to steer white blood cells into a regulatory mode, rather than an attack mode.

In order to do the same, dendritic cells need TLR2, since zymosan also activates another receptor called dectin-1, which sends out stimulatory signals.

But, the authors found that the effects of zymosan and TLR2 can deter white blood cells from attacking nerve tissue in a mouse model of multiple sclerosis.

In the model, mice are immunized against myelin, which forms a protective sheath around nerves. Injecting the mice with zymosan at the same time as immunization reduced the damage to their nerves.

The results have been published in the latest issue of Nature Medicine. (ANI)