The Role of Neuroendocrine-Immune Changes in the Pathogenesis of Infectious Mononucleosis: Approaches to Diagnosis and Therapy

The dissertation is devoted to the study of the role of neuroendocrine-immune changes in the pathogenesis of infectious mononucleosis (IM) in children from 1 to 14 years of age. The research is oriented toward a comprehensive evaluation of the functional state of the hypothalamic-pituitary-thyroid and adrenal systems, as well as the immune status of children with various clinical forms of IM, with the aim of establishing their connection with the severity and course of the disease. In the work, the diagnostic capabilities of PCR and ELISA methods in the verification of IM are compared, and the efficacy of immunocorrective therapy with the use of the interferon inducer cycloferon is evaluated. The obtained data are directed toward substantiating early prognosis of the course of the disease, improving therapeutic tactics, and expanding diagnostic approaches in pediatric practice.

Relevance of the Problem. The principal objective in the field of child health protection is the reduction of morbidity and childhood mortality. Within the structure of infectious pathology in children, infectious mononucleosis (IM) occupies one of the leading positions. Many questions of pathogenesis, clinical course, and therapy of this disease belong to the most important problems of modern pediatrics [48, 70, 81, 103, 153, 254].

Clinical manifestations of IM in children are diverse, which creates certain difficulties in timely and correct diagnosis of the disease, as well as in its differential diagnosis from diseases accompanied by a mononucleosis-like syndrome (MLS). Diagnostic errors at the prehospital stage account for from 40 to 90 percent of cases, especially in children of early age [81, 139]. In the available literature, we have not found data on the features of the clinical course of IM in children under one year of age.

To date, in many medical institutions the diagnosis of IM is confirmed only clinically, as well as on the basis of hematological changes in the form of an increased number of monocytes and the appearance of atypical forms. At the same time, the data on the degree of expression of the general and atypical mononuclear reaction in IM are contradictory. With a low percentage of atypical monocytes, the diagnosis of IM becomes doubtful. Questions of laboratory diagnostics have been insufficiently developed. Serological methods based on the detection of heterophile antibodies, proposed in the 1970s–1980s, have not found wide application in practice due to low sensitivity and specificity [96, 164, 189, 209].

In recent years, methods of molecular biology have been introduced into the diagnostics of infectious diseases, among which the polymerase chain reaction (PCR) has found wide application. It allows the detection of DNA of various viruses in biological samples with high sensitivity and specificity. The diagnostic value of PCR for the detection of Epstein-Barr virus (EBV) consists in the fact that, firstly, there are no methods for its cultivation; secondly, there are no kits for antigenic diagnostics; thirdly, antibody synthesis may be impaired when the immune response is suppressed (especially in children of early age), which may complicate the establishment of a diagnosis [39, 63, 76]. At the same time, modern data on the use of PCR in IM are isolated and contradictory [160, 196, 223, 225, 270, 321, 333, 354]. In most studies, EBV DNA is determined only in serum, investigations of other secretions are not conducted, and the obtained data are not convincing due to the small number of examined patient groups. There are no studies on comparative analysis of the results of PCR of blood and saliva with enzyme immunoassay (ELISA) of serum.

Great attention in infectology is devoted to the study of the role of infectious-toxic agents as stressors causing the mobilization of nonspecific resistance systems of the organism and the development of a general adaptation syndrome. Research of recent years has shown that there is a clear connection between the state of the endocrine system and the severity of many infectious diseases. It is known that stress, and in particular the elevation of glucocorticoids (GC) characteristic of stress, inhibit immune reactions and increase susceptibility to infectious diseases [131, 312]. At the same time, the functional state of the most important humoral systems of the organism — the hypothalamic-pituitary-adrenal (HPA) and hypothalamic-pituitary-thyroid (HPT) systems — in children with various forms of IM and their role in the pathogenesis of this disease remain insufficiently studied to date. Interrelated disturbances of these systems give rise to pathological reactions characteristic of infectious-allergic processes, however, studies illuminating this problem in IM are isolated [102].

There is an opinion that the regulatory influence of steroid and thyroid hormones on metabolic processes manifests itself primarily when there is a sharp disturbance of homeostasis and a necessity arises to adapt to extreme conditions [11]. At the same time, establishing the features of hormonal regulation may provide a number of informative laboratory indicators in determining the course and outcome of the disease. The study of the functional activity of the adrenal cortex has great practical significance, as the question of indications for the prescription of GC to patients with IM, the justification of doses and duration of treatment, remains urgent. In severe forms, GC therapy has been used for many decades [149, 160, 276], however, it is carried out without taking into account the influence of these hormones on the mechanisms and phases of adaptation of the child's organism.

IM is a disease of the immune system, in which a lymphoproliferative process occurs with the involvement of EBV subpopulations of T- and B-lymphocytes. Structural characteristics of the T- and B-systems of immunity have been studied; however, data on the number of major immunocompetent cells — CD4+ and cytotoxic CD8+ and CD16+ T-lymphocytes — are highly contradictory. There are isolated studies on the level of cytokines and their role in the immunopathogenesis of IM. At the same time, without these data it is difficult to determine whether there is an immunodeficiency or, conversely, an enhancement of the immune response in this disease, as well as to determine the necessity and correct choice of immunomodulators in therapy, and also the periods of their use.

Goal of the Research. To reveal the clinical-pathogenetic role of changes in the functional state of the hypothalamic-pituitary-thyroid, adrenal, and immune systems in children with IM for early prognosis of disease severity, improvement of therapeutic tactics, and laboratory diagnostics.

Tasks of the Research.

1. To study the clinical-laboratory manifestations of IM in children under conditions of Novosibirsk and to identify clinical features of the disease in children of breast-feeding age.

2. To conduct a comprehensive study of the functional state of the hypothalamic-pituitary-thyroid system and the adrenal glands with determination of cortisol, thyroid-stimulating hormone (TSH), thyroid hormones — triiodothyronine (T3) and thyroxine (T4) — in children of various age groups in the dynamics of the disease and at different degrees of severity.

3. To study structural changes in immune status indicators — CD3+, CD4+, CD8+, CD16+, CD19+, HLA DR+ on monocytes — and the content of immunoregulatory cytokines — IL-2, IL-4, IFN-γ — depending on the period and degree of severity of the disease, in order to substantiate immunocorrective therapy.

4. On the basis of the obtained criteria, to develop a prognosis of disease progression in order to select a rational tactic of patient treatment.

5. To determine the periods and justification for the prescription of the interferon inducer cycloferon, and to evaluate its efficacy in the complex treatment of infectious mononucleosis in children.

Scientific Novelty of the Research:

For the first time, a comprehensive evaluation of the functional state of the hypothalamic-pituitary-thyroid and adrenal systems in infectious mononucleosis was conducted, which made it possible to determine differences in adaptive mechanisms in patients with various clinical forms of the disease. A dependence of changes in hormone concentration on the degree of severity and the period of the disease was established:

- it has been shown that in the majority of children from one to 14 years of age with IM of mild and moderate-severe forms, an adequate type of response of the HPT system and the adrenal cortex to the "infectious" stress is observed: in the acute period, an adaptive increase in the secretion of TSH, T3 and T4, and cortisol occurs in relation to the control group, with a tendency toward normalization of their levels in the period of recovery;

- it has been established that in severe forms, activation of stress-representing cortisol did not occur in only 35 percent of patients, TSH in half of them, and in the majority of children in the acute period, transient hypothyroidism was observed.

For the first time, the position has been substantiated that changes in the functional activity of the hypothalamic-pituitary-thyroid and adrenal systems in IM reflect processes occurring in target organs. In mild and moderate-severe forms, accompanied by moderately expressed syndromes of intoxication, angina, hepatosplenomegaly, and lymphadenopathy, and characterized by a "balance" between the HPT and HPA systems, manifested by elevated levels of cortisol, TSH, T3, and T4. In cases of discordant interrelationships in the form of decreased levels of cortisol, TSH, T3, and T4, severe IM is observed.

For the first time, a comprehensive study of the immune status in children in the dynamics of IM was conducted:

- it has been established that the development of the immune response in children with IM occurs under conditions of a significant increase in the level of IL-2 and IL-4 in the blood, as well as CD3+, CD4+, but especially effector (cytotoxic) CD8+ and CD16+-cells, as well as B-lymphocytes (CD19+);

- in the acute period of the disease, a decrease in the ability of leukocytes of peripheral blood to synthesize IFN-γ is observed, and in severe forms, a decrease in the percentage of monocytes expressing HLA DR molecules.

It has been established that therapy with the interferon inducer cycloferon stimulates the synthesis of IFN-γ and increases the functional activity of monocytes in the dynamics of the disease, which contributes to a reduction in the duration of fever and angina in patients with IM by 1.5 days, as well as a decrease in the frequency of relapses and intercurrent diseases in the convalescence period.

Theoretical and Practical Significance:

The results of the research make it possible to expand existing concepts about changes in hormonal homeostasis in the dynamics of IM and their interrelation with clinical features of the disease. The data obtained in the examination of healthy children from 1 to 14 years of age regarding the content of cortisol, TSH, T4, and T3 in serum are used as normative.

On the basis of the study of the hormonal status in children with IM, a theoretical basis has been obtained for the introduction into clinical practice of fundamentally new methods of early prognosis of the course of the disease. Pronounced changes in the adaptive response of the organism may serve as prognostic criteria for the formation of a severe form of IM (in cases of decreased levels of T4, T3, absence of an increase in TSH and cortisol).

A moderate increase in the secretion of cortisol, TSH, T4, and T3 in the first days of the disease makes it possible to predict the development of favorable (mild and moderate-severe) forms of IM.

The rare detection of cases of hypocortisolemia and the transient character of hypothyroidism in severe forms of IM allow us to consider the use of glucocorticoids and thyroid hormones in the treatment of sick children as pathogenetically unjustified.

The conducted comparative evaluation of PCR and ELISA methods makes it possible to recommend them as the most accurate and reliable methods for the verification of IM.

The performed research expands diagnostic possibilities in IM through a comprehensive evaluation of the results of PCR of blood and saliva, and, with the application of the ELISA method, through the simultaneous determination of no fewer than two markers of the early response (IgM to VCA and IgG to VEA);

The data on changes in the cytokine spectrum supplement knowledge about the immunopathogenesis of IM, introduce new elements into the understanding of immune mechanisms of formation of the systemic inflammatory response in this disease, and make it possible to substantiate approaches to immunocorrective therapy using means directed toward self-regulation of the immune system. A significant increase in the level of IL-2, intensive proliferation of T-cells: CD3+, CD4+, but especially effector (cytotoxic) CD8+ and CD16+-cells, as well as B-lymphocytes (CD19+), allow us to conclude the inexpediency of the use of immunostimulants in the treatment of patients with IM. The propositions put forward for defense:

1. Hematological changes in children with IM residing in Novosibirsk are characterized by a moderate expression of the general mononuclear reaction and a low percentage of atypical monocytes, which dictates the necessity of confirming the etiological diagnosis.

2. In children with infectious mononucleosis at the age of 1 to 14 years, the functional state of the hypothalamic-pituitary-thyroid system and the adrenal glands changes, which influences the degree of severity of the disease.

3. The concerted response of the adrenal cortex and the hypothalamic-pituitary-thyroid system in the acute period of IM, manifested by elevated levels of cortisol, TSH, T4, and T3, contributes to a favorable course of the disease with the development of mild and moderate-severe forms; a discordant character of the hormonal profile with a decrease in the concentration of the investigated hormones makes it possible to predict a severe form.

4. Changes in various links of the immune system in IM presuppose a differentiated approach to correction. Pronounced proliferative activity of the cellular and humoral links of the immune system of peripheral blood indicates the inexpediency of the prescription of immunostimulating preparations. In conditions of decreased ability of leukocytes to synthesize IFN-γ, a decrease in the percentage of functionally active monocytes, the use of interferon inducers is indicated.

5. Cycloferon treatment exerts a stimulating influence on the synthesis of IFN-γ and the enhancement of HLA DR molecule expression on monocytes in the dynamics of the disease, which contributes to a reduction in the duration of fever and angina in patients with IM, a decrease in the frequency of relapses and intercurrent diseases in the convalescence period.

6. IM in breast-fed children proceeds with a less pronounced clinical manifestation — fever, angina, lymphadenopathy — and with a more pronounced respiratory syndrome, compared to children over one year of age.