Bacterial causes of non-pregnancy

In addition to viral infection, bacterial infection and bacterial-viral associations play a significant role in termination of pregnancy.

In recent years, studies have been published that show the role of disturbances in the normal microflora of the genital tract in premature termination of pregnancy. In sporadic termination, infection is the leading cause of loss, especially in the second and third trimesters of pregnancy. Chorioamnionitis is usually the result of ascending infection, which is more typical for the second trimester of pregnancy. Infection can directly affect the fetus, and possibly due to the activation of proinflammatory cytokines that have a cytotoxic effect. Pregnancy loss can be associated with hyperthermia, elevated prostaglandin levels, and premature rupture of the fetal bladder due to microbial proteases.

As for habitual miscarriage, the role of infection raises many controversial issues and many believe that infection in habitual miscarriage does not play such a role as in sporadic miscarriage. However, in recent years, many studies have shown the important role of infection in habitual miscarriage.

Bacterial vaginosis is found in almost half of women with habitual miscarriage of infectious origin.

Chlamydial infection, according to many researchers, is found in 57.1% and 51.6% of women with miscarriage, respectively. Screening examination of women planning pregnancy for the presence of chlamydia is proposed. According to some authors, the action of chlamydia is carried out through inflammatory cytokines. However, most researchers believe that chlamydial infection is more common in patients with infertility, rather than miscarriage.

According to many authors, group B streptococcus is often associated with fetal growth retardation and is periodically detected in cervical cultures in 15-40% of pregnant women. Infection may result in premature rupture of membranes, premature birth, chorioamnionitis, and bacterial postpartum endometritis. Diseases of newborns occur in 1-2% of infected mothers. Newborns, especially premature babies, develop diseases caused by group B streptococcus - pneumonia, meningitis, sepsis, which are very severe.

According to most researchers, miscarriage is characterized not by a monoinfection, but by a combined urogenital infection, which often occurs in a subclinical form, making it difficult to detect.

In order to clarify the role of opportunistic microorganisms in the genesis of miscarriage, we, together with the microbiology laboratory, carried out a wide range of species identification of microorganisms (representatives of opportunistic species of saprophytes, pathogens) of the vaginal microcenosis, cervix and endometrium outside pregnancy in three groups of women: with habitual miscarriage of clearly infectious genesis (chorioamnionitis, endometritis, infected fetus), with non-developing pregnancy without obvious signs of infection and in healthy fertile women.

Microbiological studies of endometrial tape scrapings in women of three groups showed that asymptomatic persistence of microorganisms in the endometrium was detected in 67.7% of women with infectious genesis of miscarriage, in 20% of women with a history of non-developing pregnancy and was not detected in the control. More than 20 types of opportunistic microorganisms were detected in the endometrium. A total of 129 strains were isolated, including obligate anaerobes, which accounted for 61.4% (bacteroides, eubacteria, peptostreptococci, etc.), microaerophiles - 31.8% (genital mycoplasmas and diphtheroids prevailed), and facultative anaerobes - 6.8% (group D, B streptococci, epidermal staphylococcus). Only 7 women had monocultures, while the rest had associations of 2-6 types of microorganisms. Quantitative assessment of microorganism growth showed that massive seeding (10 ³ -10 ⁵ CFU/ml) of the endometrium occurred only in 6 of 50 women with positive endometrial culture results. All of these women had aerobic-anaerobic associations and mycoplasmas with a predominance of coliform bacteria or group D streptococci. These patients had the most burdened anamnesis in terms of the number of spontaneous miscarriages. In the remaining women, the amount of microflora in the endometrium was within the range of 10 ² -5x10 ⁵ CFU/ml of endometrial homogenate.

A clear connection between the presence of microorganisms in the endometrium and morphological changes in the structure of the endometrium was determined. Histological verification of the diagnosis of "chronic endometritis" was carried out when infiltrates consisting mainly of lymphocytes, plasma cells, as well as histocytes and neutrophils were detected in the endometrial stroma obtained in phase I of the menstrual cycle, which is consistent with the literature data. Histological signs of a chronic inflammatory process were found in 73.1% of the examined women of the main group and in 30.8% of women of the comparative group and were not detected in women of the control group.

When comparing the results of parallel histological and microbiological examination of the endometrium obtained in the first phase of the menstrual cycle, it was found that in cases of isolation of microorganisms from the endometrium, histological signs of inflammation were detected in 86.7% of cases. At the same time, with a histological diagnosis of chronic endometritis, sterile endometrial cultures were found in 31.6% of women. These results indicate, on the one hand, the leading role of opportunistic microorganisms in the persistence of the inflammatory process in the endometrium, and on the other hand, our incomplete detection of causative agents of chronic endometritis, primarily, apparently, due to viral and chlamydial etiology, since approximately 1/3 of verified histological diagnoses of chronic endometritis were not confirmed by the isolation of the pathogen.

In addition, it was found that with the persistence of microorganisms in the endometrium, 70% of women had manifestations of dysbiosis in the vaginal microcenosis. At the same time, in the group of women with sterile endometrial cultures, the composition of the vaginal microcenosis met the criteria of the norm in the overwhelming majority of patients (73.3%).

Dysbiotic manifestations in the vaginal microcenosis consist of a sharp decrease in the amount of lactoflora, the predominance of microorganisms such as gardnerella, bacteroides, fusobacteria, vibrios, i.e., in this group of women, the obligate anaerobic component predominated in the vaginal microflora, whereas in the group of women with sterile endometrial cultures, the leading component in the vaginal microcenosis was lactobacilli.

As for the microflora of the cervical canal, sterile cultures of discharge were relatively rare in both groups (in 8% and 37.8% of women in the main and comparative groups, but statistically significantly less often in the main group of women). In cases where microorganism growth is detected in the cervical mucus in women of the main group, associations of several bacterial species are significantly more common. Such leading pathogens of purulent-inflammatory processes as Escherichia, Enterococci, genital mycoplasmas and obligate anaerobes (bacteroids, peptostreptococci) are found 4 times more often in the cervical canal of women with persistence of microorganisms in the endometrium. Gardnerella, Mobiluncus, Clostridia were found in the cervical canal only in patients with persistence of microorganisms in the endometrium.

The development of dysbiotic processes in the microcenosis of the lower genital tract is the leading pathogenetic link in the mechanism of ascending infection of the endometrium, especially in patients with isthmic-cervical insufficiency. Considering that the composition of the vaginal microcenosis is a hormonally dependent condition, a decrease in the level of vaginal colonization resistance may be associated with hormonal insufficiency, which occurred in most of our patients.

Recent studies have shown that local immunity changes against the background of chronic endometritis. If in the endometrium of healthy women outside pregnancy B-, T-, NK-cells, macrophages are presented in insignificant quantities, then in chronic endometritis there is a sharp activation of cellular and humoral inflammatory reactions at the local level. This is expressed in an increase in leukocyte infiltration of the endometrium, the number of T-lymphocytes, NK-cells, macrophages, in a sharp increase in IgM, IgA, IgG titers. Activation of local immune reactions can lead to disruption of placentation, invasion and development of the chorion and, ultimately, to termination of pregnancy if it occurs against the background of chronic endometritis.

Persisting for a long time, viral-bacterial infection can lead to a change in the antigen structure of infected cells due to the actual infected antigens included in the structure of surface membranes, and the formation of new cellular antigens determined by the cellular genome. In this case, an immune response to heterogenized autoantigens develops, leading to the appearance of autoantibodies, which, on the one hand, has a destructive effect on the cells of the body itself, but, on the other hand, is a protective reaction aimed at maintaining homeostasis. Autoimmune reactions, viral-bacterial colonization of the endometrium are among the most common etiologic factors causing the development of the chronic form of DIC syndrome.

In the event of pregnancy, autoimmune reactions and activation of infection can lead to the development of disseminated intravascular coagulation, the occurrence of local microthrombosis in the placentation area with the formation of infarctions followed by placental abruption.

Thus, chronic mixed viral-bacterial infection in patients with habitual miscarriage, persisting for a long time in the body and remaining asymptomatic, leads to activation of the hemostasis and immune systems at the local level, which are directly involved in the processes of death and rejection of the ovum.

In conditions of chronic endometritis during the gestational process, the immune system, evolutionarily determined to recognize and eliminate foreign antigens, can cause an inadequate response of the mother's body to the development of pregnancy.

Recent studies have shown that in more than 60% of women with habitual miscarriage, blood cells (lymphokines and monocytes) after incubation with trophoblastic cells in vitro produce soluble factors that have a toxic effect on the processes of embryo and trophoblast development. In women with intact reproductive function and in whom miscarriages were caused by genetic or anatomical reasons, this phenomenon is not detected. Biochemical research has revealed that the embryotoxic properties belong to cytokines produced by CD4+ cells of type 1 and, in particular, interferon.

The interferon system was formed in phylogenesis simultaneously with the immune system, but it differs from the latter. If the immune system is aimed at maintaining the constancy of the protein environment of the body, its function is to recognize and destroy foreign substrates that have penetrated the body, including viruses and bacteria, then interferon protects the body from the spread of foreign genetic information and its own genetic material from destructive effects. Unlike the immune system, the interferon system does not have specialized organs and cells. It exists in every cell, since every cell can be infected and must have a system for recognizing and eliminating foreign genetic information, including viral nucleic acids.

Depending on the source of production, interferons are divided into

• Type I - non-immune (this includes a-IFN and beta-IFN). This type of interferon is produced by all nuclear cells, including non-immunocompetent ones;
• Type II - immune - y-IFN - its production is a function of immunocompetent cells and is realized in the process of immune response.

Each type of interferon has its own gene. Interferon genes are localized on chromosomes 21 and 5. Normally, they are in a repressed state and induction is necessary for their activation. IFN secreted as a result of induction is released by cells into the blood or surrounding intercellular fluid. Initially, it was believed that the main biological role of interferon is its ability to create a state of immunity to viral infection. By now, it has been established that the effect of interferons is much broader. They activate cellular immunity by enhancing the cytotoxicity of natural killers, phagocytosis, antigen presentation and expression of histocompatibility antigens, activation of monocytes and macrophages, etc. The antiviral effect of interferon is associated with its induction of the synthesis of two enzymes inside the cell - protein kinase and 2-5' oligoadenylate synthetase. These two enzymes are responsible for inducing and maintaining a state of immunity to viral infection.

Although the interferon system does not prevent the penetration of a viral particle into the body, it sharply limits its spread. At the same time, the antiproliferative and immunomodulatory effects of interferon can make a significant contribution to the implementation of the antiviral effect of interferon. The interferon system can block the proliferation of virus-infected cells and simultaneously configure almost all links of the immune system to eliminate the pathogen. This is how the interaction of the immune system and the interferon system is connected. In this case, interferon is the first line of defense against the virus, and the immune system comes into play a little later. Depending on the dose of interferon, it affects the production of antibodies by B cells. The process of antibody formation is regulated by T-helpers. T-helpers, depending on the antigens of the main histocompatibility complex expressed on them, are divided into two subtypes Th1 and Th2. Cytokines, which include y-IFN, suppress antibody formation. All types of interferons stimulate virtually all functions of macrophages and promote the functional activity of NK cells, which carry out non-specific and antigen-dependent lysis of virus-infected cells.

During physiological pregnancy, a complex restructuring of the interferon system occurs, depending on the gestational age. In the 1st trimester, a number of authors note the activation of interferon genesis with its subsequent decrease in the 2nd and 3rd trimesters. During pregnancy, interferon is produced not only by the mother's blood cells, but also by cells and tissues of fetal origin. According to its physical and biological properties, trophoblastic interferon belongs to IFN-a and is determined in the blood of the mother and fetus. In the 1st trimester, the trophoblast produces 5-6 times more interferon than in the 3rd trimester. Under the influence of viruses, the trophoblast secretes a mixture of interferons.

One of the functions of interferon during pregnancy is to prevent transplacental spread of viral infection. During a viral infection, the level of interferon increases in both the mother's and the fetus's blood.

Another pathogenetic mechanism of antiviral activity of trophoblast interferon is associated with its ability to induce expression of class I antigens of the major histocompatibility complex on trophoblast. This leads to increased activity of cells involved in interaction with viruses: cytotoxic T cells, macrophages, NK and thus to activation of local inflammatory changes, by means of which the spread of viral infection from mother to fetus is prevented. However, excessive activation of inflammatory cytokines, including interferons, by a large dose of infection can lead to the development of immune reactions aimed at eliminating the pathogen with simultaneous disruption of normal development and function of trophoblast and placenta.

Recently, interferon-y has been considered as a cytotoxic factor in women with habitual miscarriage. It is known that the normal interferon status is characterized by a low content in serum (>4 U/ml) and a pronounced ability of leukocytes and lymphocytes to produce these proteins in response to inducers. Under normal conditions, all types of interferon are synthesized in a certain proportional relationship. Disproportion in the production of different types of interferon can lead to the development of a pathological process. Acute viral infections lead to a sharp increase in the level of serum interferon, while interferon-dependent intracellular antiviral mechanisms are simultaneously activated. In the primary episode of genital herpes, the rate of activation of the interferon system in antiviral defense is not high enough to slow down the spread of the virus. This, apparently, can be one of the reasons for the chronicity of this disease.

In recurrent viral infections, suppression of interferonogenesis processes is observed, which is expressed in background indicators of serum interferon in combination with a sharply suppressed ability of lymphocytes and leukocytes to produce a-, beta- and y-interferon. This state of the interferon system is called interferon-deficient.

In mixed chronic viral infection, the IFN status is characterized by a virtually complete absence of the y-IFN-producing capacity of leukocytes.

In autoimmune disorders, the state of the immune system and interferon is most often characterized by the presence of inverse correlations: with a normal or even elevated level of functioning of the immune system, inhibition of interferon genesis is noted.

Thus, both autoimmune pathologies and chronic viral diseases are characterized by deep suppression of interferon genesis – interferon deficiency state. The difference between them is only in the opposite dynamics of serum interferon: in autoimmune conditions the latter is elevated, in chronic mixed viral infections it remains within the background values.

The degree of suppression of interferon production indicates the severity of the chronic process and the need for adequate therapy taking into account the identified changes in the parameters of IFN status.

As mentioned above, T-helpers are divided into two types depending on the expressed antigens of the major histocompatibility complex, as well as on the type of secreted cytokines: Th1 and Th2. TM cells secrete IL-2, TNF-beta, IFN-y, which stimulate the processes of cellular immunity. Th2 cells secrete il-4, il-5, il-10, which inhibit the reactions of cellular immunity and promote the induction of antibody synthesis. During a normally developing pregnancy, starting from the early stages, Th2 cytokines - regulatory ones - predominate in the blood. They are secreted by the fetoplacental complex throughout all three trimesters and are simultaneously determined in both the decidual tissue and placental cells. Th1 cytokines (IFN-y and il-2) are synthesized in insignificant quantities compared to the amount of cytokines in the first trimester and are barely determined in the second and third trimesters. Th1 and Th2 cytokines are in antagonistic relationships. This explains the presence of high Th2 levels during normal pregnancy. Th2 cytokines are believed to block cellular immune responses, promote trophoblast development and invasion, and stimulate steoidogenesis (progesterone, hCG). The simultaneous presence of small amounts of γ-IFN is necessary to limit trophoblast invasion.

In case of clinical threat of miscarriage, the cytokine profile changes towards the predominance of γ-IFN and il-2, with a minimum content of H-4 and il-10. Most T-helpers in the endometrium of women with habitual miscarriage belong to the Th1 type. This variant of the cytokine response is accompanied by the production of il-2, γ-IFN, and this response does not depend on age or the number of previous pregnancies.

Proinflammatory cytokines activate the cytotoxic properties of NK cells and the phagocytic activity of macrophages, which are found in increased quantities in the endometrium and decidual tissue of patients with chronic endometritis and can have a direct damaging effect on the trophoblast. Th1 cytokines are known to inhibit the synthesis of human chorionic gonadotropin. In sum, the processes that induce proinflammatory cytokines inhibit and, ultimately, can stop the development of pregnancy in its early stages, thereby participating in the pathogenesis of habitual miscarriage.

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