Reuters Health Information
Jul 15, 2013
By Robert Goodier
NEW YORK (Reuters Health) Jul 15 - Measuring T-cell responses reveals exposure to hepatitis C in healthcare workers who test negative for antibodies against the virus, a new study has found.
T-cell proliferation assays may be a more sensitive test, the results suggest. But the low-level exposures that the assays can detect are highly unlikely to be a health risk for the patient or for others, according to experts who spoke to Reuters Health.
Rather, the results suggest that T-cell assays should be included in surveillance studies that monitor exposure to hepatitis C, said Dr. Barbara Rehermann, Chief of the Immunology Section of the Liver Diseases branch of the National Institute of Diabetes and Digestive and Kidney Diseases in Bethesda, Maryland, in email to Reuters Health.
Dr. Rehermann and her team published their research online June 28 in the Journal of Infectious Diseases.
They performed T-cell assays on samples from 72 healthcare workers who had been in contact with a source of the virus, most of them through an accidental stick by a contaminated needle. During six months of follow-up, none of the workers tested positive for a chronic hepatitis C infection, but nearly half had evidence of an immune response to the virus, denoted by white blood cells, not by antibodies.
"Part of the interest of this study is we're learning more about how our bodies control viruses and how quickly we're able to respond to them," said Dr. Henry Bodenheimer at Beth Israel Medical Center in New York City, who was not involved in the research.
"It seems that very low level infection can be controlled by our immune systems. That's new information. Much of the time people have relied on antibodies. Studying T-cells is a more difficult, but a novel approach," Dr. Bodenheimer told Reuters Health.
The findings may lead to new approaches to vaccine development or treatments that stimulate the immune response to fight hepatitis infection, Dr. Bodenheimer said.
But, he added, this study does not suggest that testing methods should be changed. Antibody tests can detect chronic infection, but there is no evidence that the infection detected by T-cell assays was transmissible or linked to long-term consequences in the healthcare workers, Dr. Bodenheimer pointed out.
Past studies have offered a range of estimates of the risk of transmission of the virus to exposed healthcare workers, from 0 to 10.3%, with an average of 0.5%, according to a 2005 report in Clinical Infectious Diseases (see http://bit.ly/15g4une). The reason for that variation is not clear, however.
In this new study, assays of peripheral blood mononuclear cells in proliferation found hepatitis C-specific T-cell responses in 30 out of 63 participants tested, or 48%.
Interferon-gamma enzyme assays found at least two hepatitis-specific responses in 26 out of 62 participants tested, or 42%.
Fifty-three subjects underwent both tests. Thirteen (24%) responded to both, 21 (40%) did not respond to either, and 19 (36%) responded to one but not the other.
Those who were exposed to the virus after high-risk, rather than low-risk, needle sticks had higher proliferative T-cell responses.
"Whether these T-cell responses reflect protective immunity or whether they are downstream events of protective innate immune responses or abortive replication of defective viral genomes requires further studies in suitable models," Dr. Rehermann and her team write.
In the general population, the Centers for Disease Control and Prevention now recommends that all Baby Boomers, those born from 1945 to 1965, be tested for hepatitis C.
J Infect Dis 2013.