AsianScientist (Aug. 5, 2017) – In a study published in the journal Science Immunology, scientists from China, the Middle East and the US have discovered that T-cell responses against the Middle East respiratory syndrome coronavirus (MERS-CoV) are accurate predictors of disease incidence and patient recovery.
The MERS-CoV is transmitted from infected camels to human populations. It was first identified in Saudi Arabia in 2012 and causes symptoms such as fever, cough and breathlessness. However, some infected patients are asymptomatic, and this raises difficulties in estimating the prevalence of infection.
“As of 2 August 2017, MERS-CoV has infected 2,040 people, causing 712 deaths since 2012,” said Dr. Zhao Jincun of the Guangzhou Medical University in China, the corresponding author of this study. “In comparison, influenza A (H5N1) virus has infected 859 people with 453 deaths in 14 years.”
Zhao noted that MERS-CoV has the potential to cause widespread outbreaks, citing an example from 2015 when a single patient with MERS entering South Korea resulted in 186 secondary and tertiary infections. An estimated 16,000 individuals were also quarantined.
There is currently no licensed vaccine available for MERS. While camel vaccination has been proposed, studies have shown that camels are repeatedly infected even though protective antibodies can be detected in their blood, Zhao told Asian Scientist Magazine. Efforts to develop vaccines for use in humans have also been hampered by a lack of understanding of protective immune responses.
In this study, the research team analyzed for the first time MERS-CoV-specific T-cell responses in patients. T-cells are responsible for the clearance of MERS-CoV. Specifically, a subset of T-cells known as CD8+ T-cells are necessary for the destruction of infected cells, thus halting the progress of infection.
The scientists showed that CD8+ T-cell responses can be detected in some patients with undetectable antibody responses.
“Our results, as well as those of others, show that antibody titers are often transient or low in magnitude in patients,” said Zhao. “Because previous studies of MERS prevalence rely on measurements of MERS-CoV-specific antibodies, the results of our study indicate that the true incidence of infection is much greater than current estimates.”
The researchers further examined the relationship between virus-specific antibodies and T-cell responses. Their results suggest that CD8+ T-cell responses are superior to antibody measurements as an indicator of prevalence in epidemiological studies.
Furthermore, based on correlative assessments of clinical parameters and identified T-cell epitopes recognized in some patients, the researchers concluded that patients with detectable virus-specific CD8+ T-cell responses at earlier times after infection might be expected to have more favorable outcomes. Such information will help clinicians formulate guidelines for the therapeutic use of protective blood elements from recovered patients (known as convalescent sera) and will complement measurements of virus load in predicting patient outcomes.
Going forward, the team seeks to use T-cell responses to measure the prevalence of MERS infection and better understand the role of T-cells in MERS infection.
“Together with my long-term collaborators Dr. Abeer Alshukairi at the King Faisal Specialist Hospital and Research Centre in Saudi Aribia and Dr. Stanley Perlman at the University of Iowa in the US, we are collecting camel farmers’ blood samples to test their T-cells responses and try to clarify if the actual number of people infected with MERS is higher than current estimates, since over 80 percent camels in Saudi Arabia are serological positive for MERS-CoV, while only a few cases were identified for MERS-CoV infection in this population,” said Zhao.
“Also by using a MERS mouse model, we are dissecting the immunopathogenesis of MERS-CoV infection as well as the protective role of T-cells,” he added.
The article can be found at: Zhao et al. (2017) Recovery from the Middle East Respiratory Syndrome is Associated with Antibody and T-Cell Responses.
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