Detection of class G immunoglobulins (IgG) to Helicobacter pylori in blood serum, used to diagnose antral and fundal gastritis, gastric and duodenal ulcers, as well as to monitor their treatment.
Synonyms Russian
Helicobacter, immunoglobulins class G, IgG antibodies.
English synonyms
Helicobacter pylori Antibody, IgG; Anti-Helicobacter pylori antibody, IgG (quantitative).
Research method
Solid-phase chemiluminescent enzyme-linked immunosorbent assay (“sandwich” method).
What biomaterial can be used for research?
Venous blood.
How to properly prepare for research?
- Do not smoke for 30 minutes before the test.
General information about the study
H. pylori infection is accompanied by the development of a local and systemic immune response. Following a transient increase in the titer of class M immunoglobulins (IgM), there is a long-term and significant increase in IgG and IgA antibodies in the blood serum. Determination of the concentration of immunoglobulins (serological study) is used in the diagnosis of helicobacteriosis. IgG is found in 95-100% of cases of H. pylori infection, IgA in 68-80%, and IgM in only 15-20%. Therefore, to confirm H. pylori infection, the concentration of IgG in the blood serum is determined. This analysis has a number of advantages over other laboratory methods for detecting Helicobacter.
Determining IgG in the blood does not require endoscopic examination, therefore it is a safer method of diagnosis. Since the sensitivity of the test is comparable to that of most invasive tests (rapid urease test, histological examination), it is especially useful when endoscopy is not planned. It should be noted, however, that the test does not directly detect the microorganism and depends on the characteristics of the patient's immune response. For example, the immune response of older people is characterized by a reduced production of specific antibodies (any, including to H. pylori), which must be taken into account if a negative test result is obtained for clinical signs of dyspepsia. In addition, the immune response is suppressed when taking certain cytotoxic drugs.
The IgG test can be most successfully used to diagnose primary H. pylori infection (for example, when examining a young patient with new signs of dyspepsia). In this situation, a high titer of IgG allows one to suspect an active infection. Also, a positive test result in a patient (with or without a history of signs of dyspepsia) who has not received therapy will indicate helicobacteriosis.
The interpretation of a positive test result if therapy has been carried out (or if antibiotics with activity against H. pylori have been used for other purposes) has some peculiarities. The IgG level remains high for a long time after the complete death of the microorganism (about half of patients cured of H. pylori will have high IgG titers for another 1-1.5 years). As a result, a positive test result in a patient taking antibiotics does not differentiate between an active infection and a history of infection and requires additional laboratory tests.
For the same reason, an IgG test is not the main test for diagnosing the effectiveness of therapy. However, it can be used for this purpose if the antibody titer at the time of onset of the disease is compared with the titer after the end of treatment. It is believed that a decrease in IgG concentration by 20-25% within 6 months indirectly indicates the death of the microorganism. At the same time, if this concentration does not decrease, this does not mean the therapy is ineffective. The absence of IgG antibodies during repeated analysis indicates the success of treatment and elimination of the microorganism.
The amount of IgG to H. pylori is also one of the components by which the condition of the gastric mucosa is judged (this is the so-called serological biopsy).
What is the research used for?
To diagnose diseases caused by H. pylori and monitor their treatment:
- antral and fundal gastritis;
- ulcers of the duodenum or stomach.
When is the study scheduled?
- When examining a patient with new signs of dyspepsia (primary infection with H. pylori), especially if endoscopy is not planned.
- When examining a patient with a history of dyspepsia, if H. pylori therapy has not been prescribed (or if antibiotics active against H. pylori have not been used for another reason).
- During the initial diagnosis of helicobacteriosis and 6 months after the end of the course of its therapy.
What do the results mean?
Reference values
Result: negative.
Concentration: 0 - 0.9.
Reasons for a positive result
- Active H. pylori infection:
a) a decrease in antibody titer by 20-25% within 6 months after the end of antibacterial therapy indirectly indicates the death of the microorganism;
b) the absence of a trend towards a decrease in IgG does not indicate the ineffectiveness of therapy.
- history of H. pylori infection.
Reasons for negative results:
- absence of H. pylori infection;
- death of the microorganism after a course of antibiotic therapy.
What can influence the result?
The immune response of older people, as well as patients receiving immunosuppressive therapy, is characterized by reduced production of specific antibodies, including to H. pylori, which leads to a greater number of false-negative test reactions in this group of patients.
Treatment
Treatment is aimed at achieving remission of the disease and preventing further progression of atrophy and the development of complications
- Antacids (to normalize the acidity of gastric juice).
- Gastroprotectors (drugs that protect (envelop) the mucous membrane).
- Antimicrobials.
- Prokinetic drugs.
- Individual selection of diet.
Attention!
The selection of drug therapy should be made individually, taking into account the severity of the disease, the presence of concomitant diseases, the patient’s age and the risk of possible side effects.
We ask you not to self-medicate based on Internet data!
Branch phone:
+7 (495) 695-56-95
Cellular biosensors. Amazing facts from the life of some bacteria
Any bacterial cell is an amazing mini-factory that, based on its natural niche, has developed a number of survival and adaptation mechanisms within itself, the basis of which are genes, proteins (products of gene expression) and promoters that control all these processes. A promoter is a unique sequence in front of a gene that the enzyme polymerase “recognizes,” interacts with it, and triggers a cascade of processes such as transcription (production of RNA) and translation (production of a protein product) of this gene. All this is called gene expression, and the promoter regulates this expression and its level (Fig. 2).
Figure 2. Schematic representation of the gene expression process. Gene expression is regulated by a promoter. The DNA sequence of a gene serves as a template for the process of transcription (production of RNA from the DNA sequence of a gene) and subsequent translation (formation of a protein product).
drawing by the author of the article
There are genes whose products are always needed by the cell, so they are expressed at a constant level (they are called “housekeeping” genes). And there are genes whose expression is needed only in some cases, for example, to protect the cell from adverse external influences. This effect is called a promoter inducer. And one promoter can have several such inducers at once. Sometimes a change in the amount of a protein product in a cell in response to an inducer can be easily recorded, for example visually. This is precisely what is characteristic of natural luminescent bacteria, such as Vibrio, Photobacterium, Shewanella (Altermonas) and Photorhabdus (Xenorhabdus), found mainly in the sea [8]. In their cells, using an entire operon (several combined genes), called the lux operon, the protein-enzyme luciferase and its auxiliary proteins are encoded, which, controlling a complex cascade of reactions, initiate the cell to glow with bluish-green light - luminescence [8]. Stress-sensitive promoters are responsible for the regulation of this lux operon in the cell. Accordingly, factors acting on these promoters change the expression of the lux operon and, as a consequence, the level of cell luminescence. And since everything in the household will work for a good housewife, scientists decided that it would be inappropriate for such bacteria to just disappear at the bottom of the sea and made them part of a biological sensor [9].
A biosensor is a device in which the sensitive layer is represented by a biological object: a cell (cellular biosensor), enzyme (enzyme biosensor), antibody (immunosensor) or nucleic acid (sensors based on DNA aptamers). This sensitive layer reacts to the presence of a certain component in the analyzed mixture and generates a signal (for example, in the case of luminescent bacteria, glow) proportional to the amount of this component or the fact of its presence/absence [10]. Each type of sensing element has its own advantages and limitations. But sensors based on living cells are much more stable and cheaper. In addition, the unique combination of all cellular components allows you to create a system that cannot be reproduced using individual components. Therefore, biosensor systems such as Microtox in the USA, LUMItox in the UK, ToxAlert in Germany and BioTox in Finland are already being actively used in ecology to determine the toxicity of aquatic environments based on luminescent bacteria [9], [10]. These are cellular biosensors based on native (that is, natural) bacterial cells.
But what if a bacterium has specific promoters that are sensitive to specific factors and would be useful in a biosensor, but the expression product of these genes is not convenient to record? Well, they don’t glow in ordinary life. Do not want? We'll help.
This is where the great and terrible genetic engineering comes into play, thanks to which, by the way, humanity has obtained drought-resistant wheat and cold-resistant tomatoes, larger potatoes and parasite-resistant apples and bananas [11]. How? In short, using genetic engineering methods we can introduce additional genes or entire hybrid sequences into a cell so that the cell produces the proteins we need in a larger volume or acquires new qualities thanks to them [12]. By the way, it is genetically modified bacteria that produce for us on a huge scale the hormones insulin and erythropoietin, as well as various vitamins and antibiotics, which are simply vital for many people [12].
Today, there are many options and approaches to modifying plants and microorganisms in genetic engineering. But in our case, to obtain a cellular biosensor based on genetically modified bacteria, the simplest approach is to use a reporter construct (Fig. 3) [7], [13–16]. Most often, the reporter construct is a circular DNA (plasmid), which can be introduced into a cell and exist autonomously in it. In the composition of such a plasmid we can place the promoter of a given microorganism that we select, sensitive to specific influences, so that it regulates the expression of our chosen reporter gene (this is a gene whose product is easily recorded - for example, green or red fluorescence or luminescence).
Figure 3. Simplified diagram of the operating principle of a biosensor based on modified cells using a reporter construct. As part of the construct, the sensitive promoter is combined with a reporter gene, controlling its expression. The construct is introduced into cells by cellular transformation. As a result of external influence on such construct-modified cells, the stress-sensitive promoter is activated, the reporter gene is expressed, and the subsequent production of the reporter protein occurs.
[7], figure modified and adapted
So, let's summarize. We select an interesting microorganism with an unusual, specific promoter that is sensitive to a certain substance that we would like to detect. Then we “assemble” a reporter construct for it, which contains a reporter gene under the control of a stress-sensitive promoter and introduce this construct into the cells (we genetically modify our microorganism). If there is an inducer substance in the environment to which our promoter is sensitive, the promoter activates the expression of the reporter gene, the reporter protein is produced in the cell, and we see a cellular signal - voila! We detect this substance in the environment due to the fact that the modified cells change their fluorescence/luminescence in response to the inducer substance. Based on such modified microorganisms, a number of biosensors have already been obtained, with the help of which heavy metals in the environment and soil, toxins in groundwater, toxic compounds in water and antibiotics in soil and food are successfully detected.
The most popular microorganism for modification and use in such biosensors is the opportunistic bacterium E. coli or Escherichia coli [17]. However, humanity’s needs for new specific detection systems and new microorganisms for these purposes are only growing every day. Each microorganism is unique, and the more unusual its biological niche and methods of adaptation to it, the more specific its promoters. So we decided to make our fearsome pathogen baby H. pylori useful by genetically modifying it with a reporter construct and making it part of a cellular biosensor.
