Fox Chase Cancer Center researchers say that they have discovered the defence mechanism whereby "memory" T cells protect the body from viral diseases. Published in the online edition of the Proceedings of the National Academy of Science, their study shows that lymph nodes are not just organs where immune cells reside and proliferate, but also are the sites where a major fight against the spread of an invading virus occurs.
Lead author of the study, Dr. Luis J. Sigal, says while the role of antibodies in protection has been known for a long time, the ability of memory cells (CD8T) in preventing viral diseases has been debated. He claims that his team's work provides the basis whereby memory T cells prevent viral diseases.
The body becomes "immune" from recurrence of the same disease when the immune system produces cells called lymphocytes that specifically attack and eliminate the virus at the time of infection. Most of the lymphocytes die after the infection subsides, but some remain in the body as "memory lymphocytes" and protect the body from recurrence of the disease.
Earlier, scientists used to think that in order to protect from disease, the memory T cells need to multiply in the lymph nodes, and then migrate through the blood to kill infected cells at the site where the virus entered the body-most commonly the skin, the lungs or the gut.
But to the contrary, the researcher have now shown that memory T cells protect from viral disease without the need to migrate from the lymph nodes to the site of viral entry. "It was very difficult to imagine how the memory T cells could win this race," said Sigal, because process of lymphocyte multiplication and migration may take several days while viruses multiply and spread quicker.
The researchers say that their experiments have shown the ability of memory T cells to rapidly multiply and kill target cells inside the lymph node.
"In fact we found that memory CD8 T cells already killed target cells in the lymph node and decreased viral spread to the liver and spleen when the virus just barely started to multiply," Sigal said.
The researchers conclude that memory CD8 T cells do not prevent infection, but prevent disease partly because they curb the spread of the virus from the lymph node to vital organs at very early stages of the infection.
"It's like having a security check point. Also, many cancers, like viruses, must pass through lymph nodes to metastasise, so this research may help develop vaccines that prevent tumour metastases," said Sigal.