Vol 26, No 2 (2023)

Antimicrobial function of innate immunity is mediated by the low-molecular weight peptides which are active against bacteria, fungi and some viruses. The review presents data on studies of both natural and synthetic peptides regarding the features of their structure and therapeutic effect. As a rule, the molecules of such peptides are positively charged, due to amino acid radicals capable of protonation. Spatially, antimicrobial peptide molecules are arranged as α-helices or β-layers in separate or compound assemblies. At the same time, short molecular chains, including up to 18 amino acid residues, exist as a linear or cyclic forms, remaining at the level of primary spatial structure. Natural antimicrobial peptides are predominantly produced by neutrophilic granulocytes and macrophages, as well as epithelial cells of the barrier organs. Three families of natural antimicrobial peptides have been most studied: defensins, cathelicidins, and histatins. Defensins are active against Gram-positive and Gram-negative bacteria, viruses and fungi, having anti-inflammatory and immunomodulatory activity. Cathelicidins are chemoattractants and exert antibacterial, immunomodulatory, wound healing, antitumor effects, potentially contributing to the development of autoimmune diseases. Histatins have a pronounced fungicidal effect and prevent the formation of bacterial biofilms. A detailed study on the structure and principles of action of natural antimicrobial peptides made it possible to apply this information for the in vitro synthesis of peptides thus making it possible to create multipurpose drugs based on them. E.g., synthetic peptides WR12 and D-IK8 ensure the delivery of antibiotics to infected or tumor cells, due to permeabilization of cellular membranes. At the same time, a synthetic peptide, acipensin 1, is capable of penetrating into human tumor cells without damaging them. The immunomodulatory peptide glutoxim is effectively used in anti-tuberculosis therapy. ZP2 peptide, the functional site of granulocyte-macrophage colony-stimulating factor is effective against Gram-negative bacteria (K. pneumoniae, P. aeruginosa and A. baumannii) as well as Epstein–Barr virus. Thymic immunoregulatory peptides – bestim, hepon, thymogen and imunofan are inducers of endogenous α- and β-interferon production, inhibit the development of malignant neoplasms, and possess anti-inflammatory activity. Gepon is used in the treatment of viral hepatitis, respiratory and opportunistic infections, croup syndrome and sexually transmitted infections (including genital herpes). Thus, the synthetic antimicrobial peptides are widely used in complex treatment regimens along with conventional antibiotics, antiviral, and antitumor drugs, thus making it possible to achieve higher therapeutic effect.

Currently, the treatment of persistent non-healing wounds is among the most difficult clinical issues. We studied 20 samples of normal human skin, 10 specimens from patients with acute trauma, and 9 samples from the patients with chronic wounds that did not heal within 2 months. Using multicolor flow cytometry, we found that the resident T lymphocytes (CD3⁺αβ⁺ and CD3⁺γθ⁺) are able to locally produce biologically active substances, normalize human skin homeostasis, thus promoting the wound healing. The data obtained indicate that the blood contains mainly αβ⁺T lymphocytes (p < 0.001), while the γθ⁺T cells detected in wounds represent a population similar to skin cells. We found no difference in the ratio of resident T cells in chronic and acute wounds, and healthy epithelium. Accordingly, non-healing of wounds and chronic clinical course may be caused by dysfunction of T cells. CD69 regulates γθ T cell secretion of growth factors, IFNγ, IL-17 and IL-22. The relative number of CD69-expressing T cells from the patients with acute wounds was significantly increased, if compared with cells from normal epidermis and chronic wounds (10.5%±2.3, 7.6%±1.24, and 3.0%±1.05, respectively. p < 0.001). The number of cells with the CD3⁺αβ⁺CD69⁺ phenotype did not differ significantly between all three groups under comparison. Dysregulation of T cell-mediated healing in chronic wounds is caused by reduced production of IGF-1 by resident CD3⁺αβ⁺T lymphocytes (1.7%±0.9 (p < 0.001), and CD3⁺γθ⁺ (0.44%±0.02, p < 0.001) compared to CD3⁺αβ⁺T cells derived from acute wounds (13.6%±5.6) and CD3⁺γθ⁺ (8.9%±3.1). The αβ⁺ and γθ⁺ T cells isolated from non-healing chronic wounds did not respond to mitogenic stimuli, unlike the cells obtained from acute wounds and healthy skin. In vitro analysis of cytokine secretion by the CD69-deficient dermal γθ T cells showed a lower spontaneous secretion of IL-22 (4.56%±2.3 and 23.9%±1.05 and 10.6%±1.24, respectively; p < 0.001) and IL-2 (0.9%±0.08 and 22.6%±2.5 and 3.9%±1.0, and respectively; p < 0.01). When analyzing the number of resident γθ skin T cells secreting IL-17, we obtained the following differences for healthy skin (1.4%±0.08), acute wounds (11.3%±3.2) and chronic wounds (31.7%±11.8), thus showing a significant intergroup difference (p < 0.001). T lymphocytes in chronic wounds exhibit some functional disorders and are not able to produce biologically active substances that promote physiological tissue regeneration. The results suggest a role of resident T cells in human skin in wound healing processes and provide new insights into the pathogenesis of chronic wounds.

Proteinase Activated Receptors (PARs) are the members of G-protein-coupled receptor family and can be cleaved by certain serine proteases to expose a tethered ligand domain, which binds and activates the receptors to initiate multiple signaling cascades. There is some evidence that certain proteases may regulate target cells by activating PARs. There are many studies, in which PARs play important roles in inflammation. One study indicated that PAR2 inhibition and deletion significantly suppressed the degree of inflammation due to decreased IL-6 and IL-1β levels. Another study also showed that PAR’s activation could mediate reactive oxygen species production and MAPK signaling leading to alveolar inflammation. In addition, platelet-derived CAPN1 can trigger the vascular inflammation associated with diabetes via cleavage of PAR1 and the release of TNFα from the endothelial cell surface, and sarsasapogenin may alleviate diabetic nephropathy by the downregulation of PAR1. Another Phellodendron amurense bark extract can suppress the particulate matter-induced Ca²⁺ influx caused by direct action upon PAR2, alleviating inflammation and maintaining homeostatic levels of cell adhesion components. There are also other two antagonists of I-287 and GB88, which can reduce the PAR2-mediated inflammatory reaction. In this study, we tested expression of PARs and IL-5, IL-6, RANTES and ECP release from human blood eosinophils using different enzymes and PAR agonists. The expression of PARs was assessed in human blood eosinophils by flow cytometry and RT-PCR, and the levels of cytokine and eosinophil cationic protein (ECP) in the cultured supernatants were determined with ELISA kits. Flow cytometry shows that human eosinophils express PAR2 protein and do not express PAR1, PAR3 and PAR4 proteins. RT-PCR analysis revealed expression of PAR2 and PAR3 genes in human eosinophils. Tryptase, trypsin and elastase can induce significant IL-5, IL-6 and ECP release. Trypsin and elastase may also stimulate RANTES secretion, but tryptase cannot induce the RANTES secretion. Tryptase, trypsin and elastase-induced cytokine and ECP release from human blood eosinophils most likely occurs via activation of PAR2.

Using multicolor flow cytometry, the main cytotoxic T lymphocytes (Tcyt) subsets were identified, based on the expression of CD45RA and CD62L in paired samples of peripheral blood and cerebrospinal fluid from the patients during the relapse (n = 32) and remission (n = 20) of multiple sclerosis (MS), as well as in the peripheral blood samples of healthy volunteers (n = 51). During the relapse of MS, we have observed a decreased relative number of CD3⁺CD4⁺ cells and CD4/CD8 ratio in cerebrospinal liquor. In peripheral blood taken from the relapsed MS patients, we have found significant correlations between EDSS score and absolute counts (r = -0,430, p = 0.014), and with relative numbers of CD45RA⁺CD62L⁺Tcyt (r = -0,502, p = 0.003). In remission state of MS, the relative numbers of blood CD45RA^-CD62L^-Tcyt cells exhibited a significant decrease (p = 0.005) to 8.70% (6.51-11.63) against control group with 12.18% (10.38-15.24), although it did not significantly differ (p = 0.114) from the relapsed patients with 11.31% (8.28-13.90). Studies of liquor samples have shown that, during MS relapse, the percentage of CD45RA^-CD62L^-Tcyt was increased (p = 0.027) up to 8.16% (6.40-11.40), while in remission state these cells comprised only 6.49% (4.51-8.39) from the total CD3⁺ cell number. During relapse of MS, some positive correlations were revealed between the relative number of “naïve”, CM, EM and TEMRA Tcyt from liquor, and the percentages, as well as contents of similar T cell subsets in peripheral blood samples. The inverse relationship between the level of EM Tcyt from liquor and peripheral blood “naive” cells showed the close relationship between these two Tcyt subsets and clinical manifestations of MS (i.e., scores of EDSS scale). During the remission period, most of these correlations are disrupted. Further investigations of cytotoxic T cells dynamics in peripheral blood and cerebrospinal fluid will help to approach the understanding of MS pathogenesis by revealing novel markers for the clinical prognosis in this disorder.

Our aim was to study association between proliferative activity of peripheral blood lymphocytes after COVID, and developing post-COVID syndrome, and to determine whether the cell immunity dysfunction may be regarded as its marker.

The retrospective cohort study involved 242 patients (56 males, 186 females, 18 to 85 years old) who contracted new coronavirus infection. Of them, post-COVID syndrome was diagnosed in 180 cases (duration over 3 months). The patients were classified by severity of clinical course of COVID (i.e., presence of acute respiratory disease and pneumonias), and PHA-induced blast transformation of lymphocytes. Along with PHA-induced response, we studied cyclooxygenase (COG)-producing cells by morphological method. Control group consisted of 200 healthy people without any features of coronavirus infection. All patients were questioned and examined by multidisciplinary medical team, dependent on their complaints. We also registered incidence of comorbidities associated with cellular immune deficiency.

The patients with post-COVID syndrome exhibited a decrease of PHA-induced lymphocyte proliferation as compared with control group (significant at p < 0.01 in cases of acute respiratory infection, and p < 0.05 in patients with pneumonia). Activity of COG-producing cells was similar in all groups, independently on presence of post-COVID syndrome. Classification of patients by presence of cellular immune dysfunction (PHA-induced blast transformation ≤ 50%) allowed to detect higher activity of COG-producing cells. This enzyme is known to participate in development of inflammation promoting immune deficiency, thus, probably, manifesting in clinical activation of herpesvirus infection following COVID-19. Activity of COG-synthesizing cells was found to be higher in post-COVID syndrome which evolves after middle-severe and severe forms of new coronavirus infection complicated by pneumonias.

Chronic inflammation in post-COVID syndrome associated with high activity of COG-producing cells may promote dysfunction of cell immunity, thus being a cause of evolving syndrome, like as its biomarker. Absence of the immune cell dysfunction markers among other post-COVID features leads to decreased registration of post-COVID patients and misinterpretation of the results obtained.

The immune system is a complex multiscale multiphysical object. Understanding its functioning in the frame of systemic analysis implies the use of mathematical modelling, formulation of data consistency criterion, estimation of parameters, uncertainty analysis, and optimal model selection. In this work, we present some promising approaches to modelling the multi-physics immune processes, i.e., cell migration in lymph nodes (LN), lymph flow, homeostatic regulation of immune responses in chronic infections.

To describe the spatial-temporal dynamics of immune responses in lymph LN, we propose a model of lymphocyte migration, based on the second Newton’s law and considering three kinds of forces. The empirical distributions of three lymphocytes motility characteristics were used for model calibration using the Kolmogorov–Smirnov metric.

Prediction of lymph flow in a lymph node requires costly computations, due to diversity of sizes, forms, inner structure of LNs and boundary conditions. We proposed an approach to lymph flow modelling based on replacing the full-fledged computational physics-based model with an artificial neural network (ANN), trained on the set of pre-formed results computed using an initial mechanistic model. The ANN-based model reduces the computational time for some lymph flow characteristics by four orders of magnitude.

Calibration of Marchuk–Petrov model of antiviral immune response for SARS-CoV-2 infection was performed. To this end, we used previously published data on the viral load kinetics in nasopharynx of volunteers, and data on the observed ranges of interferon, antibodies and CTLs in the blood. The parameters, which have the most significant impact at different stages of infection process, were identified.

Inhibition of immune mechanisms, e.g., T cell exhaustion, is a distinctive feature of chronic viral infections and malignant diseases. We propose a mathematical model for the studies of regulation parameters of four exhausted T cell subsets in order to examine the balance of their proliferation and differentiation determined by interaction with SIRPa⁺ PD-L1⁺ and XCR⁺1 dendritic cells. The model parameters are evaluated, in order to study the reinvigoration effect of aPD-L1 therapy on the homeostasis of exhausted cells.