Epstein-Barr virus (EBV) affects more than 90 percent of the population worldwide and was the first human virus found to be associated with cancer. Now, researchers from Harvard Medical researchers at Beth Israel Deaconess Medical Center have broadened the understanding of this widespread infection with their discovery of a second B-cell attachment receptor for EBV.
The new findings, which currently appear on-line in Cell Reports, reinforce current directions being taken in the development of a vaccine to guard against EBV, and raise important new questions regarding the virus’s possible relationship to malaria and to autoimmune diseases.
“Our discovery that CD35 is an attachment receptor for EBV helps explain several previously unsolved observations,” explains the study’s senior author Joyce Fingeroth, HMS associate professor of medicine and a member of the Division of Infectious Disease at Beth Israel Deaconess.
First discovered in the early 1960s, EBV is one of eight viruses in the human herpes virus family. The virus affects nine out of 10 people at some point in their lifetimes.
Infections in early childhood often cause no disease symptoms, but people infected during adolescence or young adulthood may develop infectious mononucleosis.
EBV is also associated with several types of cancer, including Hodgkin’s lymphoma, non-Hodgkin’s lymphoma and nasopharyngeal carcinoma, and it has been linked to certain autoimmune disorders.
“EBV was the first human virus that was discovered to be a tumor virus,” Fingeroth said. “In fact, individuals who have had infectious mononucleosis have a four times increased risk of developing Hodgkin’s disease.”
After the initial infection, the EBV virus remains in a person’s body for life.
To gain entry, viruses must first attach to their host cells. For herpes viruses, receptors on the viral envelope become connected to complementary receptors on the cell membrane. In the case of EBV, the virus gains access to the immune system by attaching to primary B cells.
Nearly 30 years ago, Fingeroth and her colleagues discovered that the attachment occurs via the CD21 protein, which until now was the only known B cell attachment receptor for EBV. The recent finding that B cells from a patient lacking CD21 can be infected and immortalized by EBV had indicated that an alternative attachment receptor must exist.
The identification of a second receptor—CD35—by Fingeroth’s team, led by first author Javier Ogembo, HMS research fellow in medicine at Beth Israel Deaconess and assistant professor of medicine at the University of Massachusetts Medical School, not only underscores an important finding regarding primary infection, but also underscores the importance of EBVgp350/220, (the virus protein that has been found to bind to both attachment receptors) for the development of a vaccine against EBV.
“The EBV glycoprotein gp350/220, is the most abundant surface glycoprotein on the virus,” said Fingeroth, adding that these results further suggest the virus fusion apparatus is the same for both receptors.
“An EBV vaccine might be able to prevent infection or, alternatively, greatly reduce a person’s risk of developing infectious mononucleosis and EBV-associated cancers, without necessarily preventing the EBV infection itself,” Fingeroth said.
Interestingly, whereas a human has now been identified to be lacking the CD21 receptor, no persons are known to lack CD35.
“CD35 is a latecomer in evolution, and in its current form exists only in humans,” said Fingeroth. “We know that it is often targeted in autoimmune diseases and was recently identified as a malaria receptor. Our new discovery may, therefore, reveal new avenues for the exploration of unexplained links between EBV, autoimmune disease, malaria and cancer.”
In addition to Fingeroth and Ogembo, study coauthors include Beth Israel Deaconess investigators Lakshmi Kannan, Ionita Ghiran, Anne Nicholson-Weller and George Tsokos; and UMass investigator Robert Finberg.
This study was supported by a grant from the National Institutes of Health (R01A10635710) as well as support from the American Heart Association, the St. Baldrick’s Foundation and the Cancer Research Institute.
Adapted from a Beth Israel Deaconess press release.