Complete Blood Count: Viral Flashbacks

7. September 2015

One new virus test system is able to track not only current infections and identify pathogens, but also provide information on latent infections and encounters with virus far back in the past. Microbiologists are still unsure whether they should cheer or remain sceptical.

Infection with Epstein-Barr virus (EBV) is so common that there is almost no-one who does not carry it in them. While usually asymptomatic, immunosuppression can however lead to serious illness. Various tumours such as Hodgkin’s disease, as well as autoimmune diseases such as multiple sclerosis and rheumatoid arthritis, are believed to be associated with the initially mostly unnoticed viral infection.

Herpes virus is probably one of the best-known examples of a latent virus infection and its effects on health, even years after the incidence of virus infection. With respect to many other short and long term virus residents it is not known exactly what traces are left behind in the body by them and how the body responds to their presence. Some viruses, such as chikungunya or MERS, were until recently largely unknown – at least in our region – as were the symptoms of their infection.

Complete virus history

Using one new test, many of the questions about the presence of new viruses and about those whose presence dates back to a much earlier time in the human operating system could be tackled and solutions found more easily. This is because authors at the prestigious Harvard Medical School in Boston produced a Science article [Paywall] describing a completely new approach to virus analysis. A mere few microlitres of blood are sufficient to detect all infections which have occurred in the body since early childhood. In addition, this test is relatively low cost at around 25 US dollars when performed by a laboratory on a large scale. After two to three days, the patient learns the names of his or her current and former residents.

The current virus tests are based either on the search for virus-specific nucleic acid sequences or on serological tests which detect the viral proteins or the antibodies produced by the immune system. However the end result here is that one always only finds a singular or perhaps a few strains of virus. Nucleic acid tests also only discover current infections in the sample tissues received. The new type of test in contrast reacts to all previously known human pathogenic viruses.

Phage peptides catch antibodies

The method which the researchers employed in their development is based on a so-called phage display. The researchers synthesised more than 90,000 oligonucleotides which occur as constituent portions found in the sequences of approximately 200 types of viral attachment to human host. The overlapping sequences at their ends are cloned in bacteriophages (T7), so that in each case a phage produces a 56 amino acid peptide from the corresponding oligonucleotide and presents the peptide on its surface. Mixed with blood or a reference sample containing antibodies against the relevant viral peptides, only these antibodies bind onto the phage.

The complexes of phage-including antibodies can then be precipitated and analysed using a high-performance DNA sequencer. The sequence then yields the references to the origin of the virus-linked peptide which the antibodies have captured. Since almost all virus infections in humans leave traces in the form of antibodies, the test can document past and present reactions of the immune system against the invaders.

Virome – reflection of the culture

The sensitivity of the new approach in determining the human virome is surprisingly high and is according to the researchers between 95 and 100 percent. “We have not had any false positive results in subjects who,” says senior author Stephen Elledge, “in reality were negative.”

Used in a small study involving 569 subjects in the USA, South Africa, Thailand and Peru, the test was convincing straight off. With a total of 106 million peptide antibody-bonds, the participants were subjected to an average of ten different viral infections hitherto in their lives; in some people though this number rose to as much as 84. Participants from the United States had a smaller average virome than those of the other countries whose health care system and hygienic conditions were less sophisticated. Likewise, a HIV infection favoured the incidence of other viruses. The fact that many infections take place at an advanced age is shown by the fact that in children fewer different antibodies are able to be found than in adults.

Problem: nonlinear epitopes

Most commonly found, as expected, were the Epstein-Barr virus (HHV-4, 87%), rhinoviruses A and B and adenoviruses (around 70%). In the case of larger viruses there were on average more reactions to more different antibodies in the test, probably due to the higher number of available epitopes. For smaller viruses, but also with influenza and poliovirus, the researchers found a lower antibody rate than expected due to contamination and high vaccination coverage. This demonstrates the limitations of the test prototype. Perhaps, an explanation by the authors, during an infection the antibodies produced recognise the discontinuous epitopes of viral tertiary structure which cannot be represented by a 56 amino acid long peptide test.

The results of this first major virus screening also indicate that the immune system makes use of so-called “public epitopes” in order to combat intruders. Against the same virus, it generates almost always very similar antibodies that recognise a specific subject on the surface. A particular combination of 5 peptides was found in 99 percent of all examined blood samples. This finding could play an important role in the future in as far as the development of adjuvants and vaccines to be used in vaccine production are concerned.

Scepticism during routine clinical use

“There are a number of chronic diseases in which a virus infection could be involved,” says Vincent Racaniello from New York’s Columbia University. “So far, we have not been able to nail it down […] and not prove the connection correctly. The new test could help us enormously. The approach is really cool”. German experts see matters somewhat more critically: “This test is not intended for the diagnosis of individual infections”, says Thomas Mertens, current president of German virologists. “I see currently no benefit for everyday clinical practice”. However, he also admits that the method can help to better identify correlations between viral infections and diseases.

Previous weaknesses would need to be eradicated, especially with regard to the detection of small viruses; the same can be said about the identification of nonlinear epitopes. Viruses that acquire their immunogenic structure through a modification after protein synthesis (post-translational modification), also fail to fit into the arrangement. A direct test using a specific nucleic acid detection in the instance of recent infection is probably for many viruses still somewhat more sensitive.

Nevertheless, this whole new approach will in its analysis of the human virome also offer several possibilities in the clinical field after it passes through the optimisation process. Deferred asymptomatic viral infections can play a role in the efficiency of chemotherapy when it is used in oncology. Revealing this role would probably raise the success rate. Available evidence indicates that the emergence of diseases such as type-1-diabetes, inflammatory bowel disease and multiple sclerosis depends on the immune system’s response to invading viruses. If we were to know more about the viral past of these patients, we would surely be casting more than just a tiny fragment of light into our understanding of the development of their ailment.

Original publication:

Comprehensive serological profiling of human populations using a synthetic human virome [Paywall]
George J. Xu et al.; Science, doi: 10.1126/science.aaa0698; 2015

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Medicine, Pharmaceutics, Studies

1 comment:

Can this be involved in the Syndrome of Chronic Fatigue ?

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