The investigation is conducted by ViroScan

Maria Valieva, "Biomolecule"A method of global immunity scanning for the presence of various antiviral antibodies in human blood has been developed.

What does this give us? Scientists-immunologists – interesting fundamental knowledge and promising areas of research. For practicing doctors – a ground for reflection and help in work. And this article is devoted to the principle of a new approach.

There is no doubt about the importance of diagnosing human viral diseases: chronic, acute and even long-term. To successfully treat people, you need to understand which viruses the body has developed immunity to. Antibodies – special protein molecules that help to recognize foreign objects that have entered the body - serve as an intermediary between the cells of the immune system and pathogens. (Immunity research is one of the most popular and promising in our days. With their help, new generation drugs are being developed – "Ebola virus and Rhesus macaques: a new effective medicine has been obtained" [2], and Nobel Prizes are also given for them - "Immunological Nobel Prize (2011)" [3] – Ed.). The human immune response usually develops within 10-14 days after contact with an infection [1], and the "memory" of it often persists for many years. It remains in the form of antibodies that circulate in the blood. Thus, by studying the immune system, it is possible not only to determine which viruses a person is currently infected with, but also to find out what infections he has already suffered.

Why can people's health be affected by their viromes – the totality of all those viruses that have managed to infect an individual? Firstly, viruses can cause acute and chronic diseases. Secondly, they leave a trace in the immune system and even sometimes have a positive effect on it: by stimulating, they help fight other pathogens. Interactions of virom and immunity are also involved in the development of multifactorial diseases, such as type I diabetes, intestinal inflammation and asthma. (VirOm, genome, transcriptome... About the types of large-scale objects of study in modern biology, that is, about -omics and –omics, read the article "Omics - the era of big biology" [4]. – Ed.)

Until now, doctors and scientists have analyzed human antiviral immunity using an individual approach – purposefully looking for antibodies against a specific virus, testing the clinical hypothesis. However, it would not be superfluous to have a method that allows you to find all human antiviral antibodies simultaneously, in a high-performance format. A large international team of scientists has developed such an approach [5].

The new method is called ViroScan (VirScan), and it makes possible the advanced analysis of antibodies to a wide range of viruses in human blood serum. This approach is able to register the immune response to all human viruses simultaneously and is designed to help establish a link between past viral infections and current diseases, as well as population characteristics. So, what is the principle of the Viroscan?

Proteins of human viruses are recognized by the immune system when they enter the body. ViroScan searches for antibodies to such proteins in the blood serum – "traces" of primary contacts. This can be achieved as follows. The gene encoding the viral protein (the main viral antigen) is placed in a bacteriophage by genetic engineering methods. Moreover, this insertion is not made in an arbitrary place of the phage genome, but in such a way that the synthesized protein is exposed on the surface of the viral particle – only in this case the protein will be recognized by the immune system. A whole "library" of such bacteriophages is being created, carrying antigens of many viruses on their surface, and then it remains only to add a drop of blood (Fig. 1). The antibodies present in the blood bind the proteins of only those viruses to which the blood donor is immune. Next, all the antibodies are extracted from the system and look at what has connected with them. The DNA of bacteriophages "selected" by antibodies is sequenced [6, 7] and it is found out which "foreign" viral proteins were encoded in it, and therefore, to which viruses the donor has immunity.

Figure 1. The method of simultaneous determination of antibodies to all known human viruses – ViroScan. 

a is the principle of the method. Each row is a specific virus, the column is a blood sample; the color of the cell reflects the relative number of virus peptides (antigenic epitopes) detected by antibodies. 

b – Stages. The approach is based on a combination of DNA microarray production, phage display, immunoprecipitation and DNA sequencing (phage immunoprecipitation sequencing - PhIP-seq technology). 

Recombinant T7 bacteriophages collected in the library carry various peptides (56 amino acids each) of human viruses on their surface, and antibodies (At) from the donor's blood bind these proteins – if the immune system has previously encountered the corresponding virus. Sequencing the amplified DNA of bacteriophages associated with antibodies, it is possible to understand what peptides were on their surface, and to restore the spectrum of viruses to which the blood donor is immune. Drawings from [5], adapted.

For such an analysis, only one microliter is enough (!) blood. Scientists believe that if the virom analysis procedure is put on stream, it will be possible to reduce the cost to $ 25 per sample. It is important to note that with the discovery of new viruses, it will be quite easy to include them in the library. Contacts with other pathogens (fungi, bacteria, protozoa) can also be tracked in a similar way.

During the testing of VIROSCAN, scientists analyzed the blood serum of 569 people from four countries located on different continents. At the same time, scientists encountered more than 108 peptide-antibody interactions, analyzed 206 species and more than 1,000 strains of human viruses. The characteristics of the new approach turned out to be encouraging. ViroScan was compared with other commercial methods for determining viral infections (for example, enzyme immunoassay (ELISA, ELISA)), and it showed high efficiency: the specificity and sensitivity of Viroscan exceeded 95% for most viruses, the method was able to distinguish even closely related viruses.

After making sure that the method works, the scientists decided to analyze which viruses people from different countries face. It turned out that on average a person is immune to 10 viruses out of 206 studied, but there were also unique cases. Five people turned out to have antibodies to 62 viruses, and two – to 84! As expected, resistance to widespread agents (Epstein-Barr virus (EBV) and other herpesviruses, rhinoviruses and adenoviruses) in adults was often recorded, but not to rare viruses.

ViroScan also allows you to determine which vaccinations the subjects did. However, it turned out that antibodies to influenza viruses (A and B) and poliovirus are less common than can be assumed based on how many people carry the corresponding infections or are vaccinated. Apparently, this is due to the fact that humoral immunity (B-cell memory) to such pathogens gradually weakens, since they are not constantly present in the body.

Scientists compared the antibody profiles of people from the USA, Peru, Thailand and South Africa. On average, donors from outside the United States had a larger set of antiviral antibodies, but residents of the States were distinguished by an increased content of antibodies to the relatively rare influenza virus type B – thanks to vaccination. There were also "fair" infectious agents that evenly infected people in all regions, such as rhinoviruses and EBV.

The authors of the work drew attention to an interesting point: memory B cells found in different people, as a rule, produce the same antibodies against a virus. That is, even if the virus protein is large and can be recognized by the immune system in several places, antibodies are produced mainly to the most immunogenic protein fragment. This suggests that the B-cell response of humans is very stereotypical. However, the choice of an immunogenic peptide differs in people from different continents. The reason may be that the viruses themselves are slightly different in different parts of the world.

So, with the help of a new approach, it has already been possible to describe the immune response of a large group of people. Preliminary studies have revealed interesting general properties of the human immune system and some geographical and age-specific features of its response to the invasion of viruses. ViroScan can become an important tool for understanding the host-virus relationship, their impact on health and the development of diseases – even at first glance, unrelated to viral invasion.

Literature

30.06.2015