Emory scientists provide new details about long-term immune memory boost vaccine development

April 03, 2001

New discoveries about how individuals acquire long-term immunity against diseases are proving essential for the development of new vaccines for complex and persistent diseases such as HIV, malaria and tuberculosis. Rafi Ahmed, Ph.D., director of the Emory University Vaccine Center and a Georgia Research Alliance Eminent Scholar, will discuss the links between mechanisms of long-term memory and vaccines in a lecture at the Experimental Biology 2001 Meeting in Orlando on April 3.

Dr. Ahmed is one of three immunologists selected to deliver the American Association of Immunologists Distinguished Lecture at this year's meeting.

In the past, scientists used a hit-or-miss approach to the development of vaccines for diseases like polio, yellow fever or measles.

Vaccine development for diseases such as HIV, however, which are expert immune-system evaders, require a detailed understanding of exactly how the immune response works.

Acute viral infections produce two types of long-term memory - humoral immunity, in which B cells produce antibodies to prevent infection by viruses, and cellular immunity, in which T cells activated by specific viral antigens kill the virus-infected cells and also produce cytokines -- proteins that prevent the growth of viruses and make cells resistant to viral infection.

Dr. Ahmed and his colleagues previously found that plasma cells, the B cells that produce antibodies, live for quite a long time--sometimes for the entire life of an organism --which helps explain why humoral immunity is capable of such long-term persistence. The other aspect of immunity - the response of T cells to viruses - is much different than the B cell response, Dr. Ahmed explains. CD4 T cells and CD8 T cells, which kill virus-infected cells, are of three types: naïve cells, effector cells or memory cells. Following exposure to virus or vaccination, T cells respond in a phase called "antigen-driven expansion," in which naïve T cells are activated and undergo a dramatic 50,000- to 100,000-fold increase in number, resulting in an expanded population of cells. These effector cells kill virus-infected cells or produce cytokines. The effector-cell response lasts for only a few weeks, then the majority of effector cells die and about 5-10% become memory cells. When memory cells come into contact with the original virus, they mount an immediate, strong and rapid immune response.

Dr. Ahmed and his colleagues believe their recent findings about long-term memory hold the keys to successful vaccine development: As scientists struggle to create long-term, effective vaccines for difficult diseases, they need a detailed understanding of the mechanisms of long-term memory, Dr. Ahmed points out. "Understanding immune memory is the necessary basis for developing any effective vaccine. No matter what type of vaccine you are working on, or for which disease, you need to understand the details of immune memory."
Dr. Ahmed's research was funded by the National Institutes of Health (NIH).

Emory University Health Sciences Center

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