Thymic Lobes Research Articles

Microsurgical assessment of thymus vascular anatomy

BackgroundThe thymus is pivotal for immune system development by facilitating T-cell maturation. Current treatments for congenital athymia typically involve avascular transplantation of allogeneic thymic tissue. However, vascularizing an infant thymus for transplantation could offer improved outcomes, necessitating a detailed understanding of its vascular anatomy. MethodBetween June and November 2022, we conducted a feasibility study at our tertiary care university hospital, examining seven thymus glands that were surgically removed and discarded during corrective surgeries for congenital heart disease in patients aged 16 days to 17 months. ResultsAngiographic analysis revealed distinct vascular pathways in infant thymic lobes, with arteries averaging 0.5 mm and veins 0.8 mm in diameter, both showing adequate perfusion with Belzer solution. ConclusionThese findings provide critical insights into the vascular anatomy of the infant thymus, underscoring its potential for microvascular revascularization and transplantation.

Cardiac herniation post left upper lobectomy and thymectomy: a case report

BackgroundCardiac herniation occurs when there is a residual pericardial defect post thoracic surgery and is recognised as a rare but fatal complication. It confers a high mortality and requires immediate surgical correction upon recognition. We present a case of cardiac herniation occurring post thymectomy and left upper lobectomy.Case presentationInitial presentation: A 48-year-old male, hypertensive smoker presented with progressive breathlessness and was found to have a left upper zone mass confirmed on CT biopsy as carcinoid of unclear origin. PET-CT revealed avidity in a left anterior mediastinal area, left upper lobe (LUL) lung mass, mediastinal lymph nodes, and a right thymic satellite nodule. Intraoperatively: Access via left thoracotomy and sternotomy. The LUL tumour involved the left thymic lobe (LTL), left superior pulmonary vein (LSPV), left phrenic nerve and intervening mediastinal fat and pericardium, which were resected en-masse. The satellite nodule in the right thymic lobe (RTL) was adjacent to the junction between the left innominate vein and superior vena cava (SVC). The pericardium was resected from the SVC to the left atrial appendage. Clinical deterioration: Initially the patient was doing well clinically on day 1, however there was sudden bradycardia, hypotension, clamminess, and oligoanuria, with raised central venous pressures and troponins. ECG: no capture in leads V1-2, but positive deflections seen on posterior leads. Echo: no acoustic windows, but good windows seen posteriorly. CXR: left mediastinal shift. Redo operation: After initial resuscitation and stabilisation on the intensive care unit, on day 2 a redo-sternotomy revealed cardiac herniation into the left thoracic cavity with the left ventricular apex pointing towards the spine, and inferior caval kinking. After reduction and repair of the pericardial defect with a fenestrated GoreTex patch, the patient recovered well with complete resolution of the ECG and CXR.ConclusionCardiac herniation can even occur following sub-pneumonectomy lung resections and should be considered as a differential when faced with a sudden clinical deterioration, warranting early surgical correction.

Type 1 immunity enables neonatal thymic ILC1 production.

Acute thymic atrophy occurs following type 1 inflammatory conditions such as viral infection and sepsis, resulting in cell death and disruption of T cell development. However, the impact type 1 immunity has on thymic-resident innate lymphoid cells (ILCs) remains unclear. Single-cell RNA sequencing revealed neonatal thymic-resident type 1 ILCs (ILC1s) as a unique and immature subset compared to ILC1s in other primary lymphoid organs. Culturing murine neonatal thymic lobes with the type 1 cytokines interleukin-12 (IL-12) and IL-18 resulted in a rapid expansion and thymic egress of KLRG1+CXCR6+ cytotoxic ILC1s. Live imaging showed the subcapsular thymic localization and exit of ILC1s following IL-12 + IL-18 stimulation. Similarly, murine cytomegalovirus infection in neonates resulted in thymic atrophy and subcapsular localization of thymic-resident ILC1s. Neonatal thymic grafting revealed that type 1 inflammation enhances the homing of cytokine-producing thymus-derived ILC1s to the liver and peritoneal cavity. Together, we show that type 1 immunity promotes the expansion and peripheral homing of thymic-derived ILC1s.

Intravital two-photon microscopy of the native mouse thymus.

The thymus, a key organ in the adaptive immune system, is sensitive to a variety of insults including cytotoxic preconditioning, which leads to atrophy, compression of the blood vascular system, and alterations in hemodynamics. Although the thymus has innate regenerative capabilities, the production of T cells relies on the trafficking of lymphoid progenitors from the bone marrow through the altered thymic blood vascular system. Our understanding of thymic blood vascular hemodynamics is limited due to technical challenges associated with accessing the native thymus in live mice. To overcome this challenge, we developed an intravital two-photon imaging method to visualize the native thymus in vivo and investigated functional changes to the vascular system following sublethal irradiation. We quantified blood flow velocity and shear rate in cortical blood vessels and identified a subtle but significant increase in vessel leakage and diameter ~24 hrs post-sublethal irradiation. Ex vivo whole organ imaging of optically cleared thymus lobes confirmed a disruption of the thymus vascular structure, resulting in an increase in blood vessel diameter and vessel area, and concurrent thymic atrophy. This novel two-photon intravital imaging method enables a new paradigm for directly investigating the thymic microenvironment in vivo.

Thymus Tissue Regeneration in 22q11.2DS Mouse Models (DiGeorge) using Mesenchymal Cell Replacement or Vasodilators

Thymus hypoplasia occurs in several clinical conditions including 22q11.2 deletion syndrome (22q11.2DS). 22q11.2DS is the most common human microdeletion disorder, affecting ~1/2100. Thymuses from 60–70% 22q11.2DS patients are smaller and produce fewer T cells than normal. For individuals with a severe hypoplasia, an allogenic thymus tissue graft is needed to restore thymopoiesis. To determine the molecular mechanisms contributing to a small thymus, we compared the subsets of cells needed for the development of the thymus using embryos from various 22q11.DS mouse models and controls. Reaggregate fetal thymic organ culture assays revealed that replacing mesenchymal cells from 22q11.2del hypoplastic lobes with normal ones restored tissue expansion and thymopoiesis. Thymic epithelial cells and endothelial cells used as substitutes did not. Single cell RNA sequencing of normal and hypoplastic thymus lobes revealed differential expression of transcripts that primarily impacted 5 distinct mesenchymal cell subsets and the one endothelial cell group in 22q11.2DS. These transcripts are involved in extracellular matrix modeling, collagen deposition, cell-cell interactions, and growth. Thymus growth in 22q11.2DS tissues was restored in RTOC assays in the presence of vasodilators, minoxidil or PGE2. We now report that timed in utero exposure of 22q11.2DS mouse embryos with minoxidil restores thymus tissue expansion. Such findings suggest novel strategies aimed at preventing thymic hypoplasia in utero that may have clinical value.

Harnessing spatial transcriptomics to study fate decisions and lineage specification in T cell development

Abstract T cells are critical components of the adaptive immune system; they develop from bone-marrow derived precursors that migrate to the thymus. There, precursors undergo a sequence of lineage specification and commitment steps that give rise to multiple T cell lineages serving essential functions in defenses against infection and immune homeostasis. The diversity of thymocytes, and their complex interactions with the thymic stroma, including epithelial cells and other hematopoietic compartments, have hampered our understanding of T cell development. For greater insight into intrathymic developmental trajectories and their transcriptional control, we and others have utilized single cell RNA- and ATAC-sequencing (scRNA-seq and scATAC-seq). However, single-cell approaches do not assess contextual cell-cell interactions. To address this limitation, we used in-situ transcriptomics, specifically the 10× Genomics “Visium” technology, which assays in-situ gene expression in 55-micron spots spanning whole mouse thymus lobes. We will present initial results of these experiments, including mapping of thymocyte differentiation stages, location of developmental bifurcations, and the spatial progression of lineage specific gene expression. Briefly, we use statistical models informed by scRNA-seq data to infer the location, relative to the thymic architecture, of lineage decisions. Additionally, we combine positional information of thymocytes and stromal cells to infer cell-cell interactions that direct lineage decisions. Collectively, this analysis sheds light on the interactions that guide development of the diverse T cell family from a common precursor and characterizes the journey of these cells to reach maturity.

Two cases of pneumomediastinum in full-term newborns after uncomplicated vaginal deliveries: Various etiologies and radiographic appearances

Pnemomediastinum is defined as the presence of aberrant air in the mediastinum, also known as mediastinal emphysema. Significant pneumomediastinum is rare, particularly in term neonates. It is usually related to the different predisposing factors such as birth injury, meconium aspiration, assisted ventilation or infectious diseases although it may occur idiopathically. Pneumomediastinum is one of the important causes of respiratory distress syndrome that should not be overlook in term neonates. The elevation of thymic lobes off the heart on plain view and the presence of retrosternal air collection on lateral view are crucial signs on chest x-rays that need to be assessed cautiously by radiologists and neonatologists. We report two cases of pneumomediastinum in term infants who presented with respiratory distress. One case was diagnosed as pneumomediastinum and assisted ventilation was supposed as a predisposing factor, the other case was diagnosed as spontaneous pneumomediastinum without underlying lung disease or predisposing factors. The definitive diagnosis was made by combination plain and lateral chest x-rays without further imaging method was required. Both patients received conservative treatment with close observation clinically and radiologically and were discharged after several days in good condition.

Multidetector Computed Tomographic Evaluation of the Normal Characteristics of the Thymus in the Pediatric Population.

The objective of the present study was to determine the morphologic features and measurements of the normal thymus on contrast-enhanced multi-detector computed tomography (MDCT) in subjects from the newborn period up to 18 years of age. The MDCT scans obtained from 464 children with a mean age ± SD of 8.43 ± 5.60 years were retrospectively re-evaluated. The shape, margins, side predominance, density, and measurements of the thymic gland were defined for each age group. A triangular thymic shape with a middle location and straight lateral contours were the most frequently seen morphologic features in children. The mean anteroposterior and transverse diameter of the thymus was 17.32 ± 4.58 and 29.99 ± 11.42 mm, respectively. The mean values for the width and thickness were 20.66 ± 5.36 and 15.15 ± 6.76 mm for the right thymic lobe, respectively; and 26.14 ± 7.85 and 14.91 ± 5.51 mm for the left, respectively. The transverse diameter of the thymus and thymic lobe dimensions decreased significantly with age, however, the anteroposterior diameter of the thymus was not significantly associated with age. Girls had higher mean thymic attenuation values compared to boys, however, this gender difference was not statistically significant (63.8 ± 22.4 HU vs. 60.1 ± 25.3, p = 0.164). Our study provides a better understanding of the normal thymic appearances in children that can aid in accurate diagnosis and avoid unnecessary, costly, and invasive interventions.

The unilateral involution in the thymus of a 96-year-old male leads to the preservation of structural integrity in one thymic lobe, as assessed by the expression of medullar and cortical antigens and the presence of CD3+ cells

The process of thymic involution begins soon after birth and continues through adult life. Although evolutionary conserved in all vertebrates, the thymic involution has no defined kinetics. Little is known about the pace of its regression in humans, except that there is a marked increase of thymic involution after puberty. This report describes the unusual structural findings in the thymus of a 96-year-old male. The morphological parameters of the organ were evaluated using H&E and immunohistochemistry (IHC) techniques. The macroscopic examination showed a typical organ's weight and size, except that the right thymic lobe presented a well-preserved organ and the left lobe was significantly adiposed. The H&E staining of the thymic sections from the left and right lobes confirmed advanced thymic adiposity in the left lobe and preserved thymic epithelial space containing hematoxylin-stained cells in the right lobe. The multiplex immunostaining of the right lobe sections with antibodies specific to cytokeratins -14 and -8, CD3, and CD4 revealed the presence of medullar and cortical epithelium and mix population of CD3+/CD4+ and CD3+/CD4- T cells. The T cells were associated with the medulla but not with the cortex of the thymus. The immunostaining with an antibody to FoxN1 showed that the protein was expressed in the thymic epithelium. Taken together, we provide evidence that the thymus of a 96-year-old man involuted different kinetics in each of the two thymic lobes. Furthermore, the presence of CD3+/CD4+ and CD3+/CD4-cells gives a hand to the hypothesis that a pool of T-cells may associate with this primary lymphatic organ for as long as there is the available thymic epithelium and be a source of lymphocytes aiding adaptive immune responses to old age.

MORPHOLOGICAL STUDY OF THE COMPONENTS OF THE THYMUS CELLULAR IMMUNE RESPONSE IN LABORATORY RATS WHEN CALCIUM IS SUPPLIED WITH DRINKING WATER

The study of the structural and functional features of the thymus is relevant, since lymphopoiesis takes place in it, it is responsible for the effectiveness of the cellular immune response of both innate and acquired immunity. The purpose of this work was to study the morphological structures of CD3-positive structures of the thymus in laboratory animals when using calcium salt supplied with drinking water. Quantitative indicators of CD3-positive thymus cells were studied using the immunohistochemical method. For the general histological characteristics of the thymus, hematoxylin and eosin staining was used. During the experiment, the animals received daily an average of 8.1–10.2 mg /kg of calcium with drinking water. It can be stated that intake of drinking water with a calcium concentration of 235 mg / l leads to an increase in the average size of the lobular area, mainly due to the cortical substance. An increase in the relative number of large lymphocytes in the cortical substance of the thymus lobes occurs due to a decrease in the number of medium and small cell forms. As for the percentage of large and small CD3-positive cells in thymus structures, in the experimental group of animals the authors observed a decrease in small cells in the medulla and at the border between the cortical and the medullary substances due to an increase in the number of large and medium thymus cells, respectively.

22q11.2 Deletion Syndrome Causes a Thymus Hypoplasia Corrected by Mesenchymal Cell Replacement

Abstract Thymus hypoplasia occurs in several clinical conditions including 22q11.2 deletion syndrome (22q11.2DS). 22q11.2DS is the most common human microdeletion disorder, affecting 1/4000. Thymuses from 60–70% 22q11.2DS patients are small and produce fewer T cells than normal. For individuals with a severe hypoplasia, an allogenic thymus tissue graft is needed to restore thymopoiesis. To determine the molecular mechanisms contributing to a small thymus in 22q11.2DS, we compared the development of the thymus in embryos from various 22q11.DS mouse models, normal controls and Foxn1 mutant mice. Reaggregate fetal thymic organ culture assays reveal that replacing mesenchymal cells from 22q11.2del hypoplastic lobes with normal ones restores tissue expansion and thymopoiesis. Thymic epithelial cells used as substitutes cannot. This is distinct from the Foxn1 mutant mice, wherein defective thymic epithelial cell functions lead to thymus hypoplasia/aplasia. Single cell RNA sequencing of normal and hypoplastic thymus lobes revealed differential expression of transcripts that primarily impacted 5 distinct mesenchymal cell subsets in 22q11.2DS. These transcripts are involved in cell-cell interactions, collagen deposition and growth. Elevated levels of collagen are present in the hypoplastic thymus tissues, suggesting a structural restriction. Mesenchymal and epithelial cell differentiation/expansion assays reveal a selective reduction in mesenchymal tissue expansion due to 22q11.2DS Supported by grants from the National Institutes of Health (R01AI114523, R21AI144140) and the Jeffrey Modell Foundation (MdlM, CAW)

Histomorphological Study of Thymus in Japanese Quail (Coturnix coturnix japonica)

Background: Thymus is the primary lymphoid organ in avian. It is a site of differentiation and maturation of T lymphocytes. Quail thymus showed age related involution with decrease in its volume and cellular contents. It is a lymphoepithelial organ and thus plays a major role in the anti-infection defense mechanism. Methods: For the present study 48 Japanese quail birds reared and thymus was collected from 12 birds each at end of first week, second week, third week and fourth week. The tissue was processed for routine paraffin embedding and processed for different staining procedures for histomorphological studies. Result: In all age group of birds, each thymic lobe was enclosed by thin connective tissue capsule. Thymic lobule was found to be composed of outer cortex and inner medulla. Cortex was composed of lymphocytes, lymphoblasts, myoid cells, macrophages, plasma cells and epithelial reticular cells and that of medulla was composed of lymphocytes, lymphoblast, epithelial reticular cells, myoid cells, macrophages, plasma cells, cyst and Hassall’s corpuscles. The cyst of various shapes and sizes were observed in cortex and medulla. In all age group of birds, unilamilar and multilamilar Hassall’s corpuscles were observed. Number of Hassall’s corpuscles and macrophages were increased with the advancement of age.

Robotic-assisted minimally invasive thymectomy for myasthenia gravis with thymoma.

Robotic-assisted minimally invasive thymectomy for myasthenia gravis with thymoma.

The Unilateral Involution in the Thymus of a 96-Year-Old Male Leads to the Preservation of Structural Integrity in One Thymic Lobe, as Assessed by the Expression of Medullar and Cortical Antigens and the Presence of CD3+ Cells

The Unilateral Involution in the Thymus of a 96-Year-Old Male Leads to the Preservation of Structural Integrity in One Thymic Lobe, as Assessed by the Expression of Medullar and Cortical Antigens and the Presence of CD3+ Cells

Morphological alterations of Thymus during the early murine leishmaniasis.

Leishmaniasis is a neglected and endemic disease that affects poorest population mainly in developing countries. Thymus provides an essential complex environment for T cell maturation and differentiation during leishmania infection. The aim of this study was to investigate the pathological alterations of the Thymus during early Leishmania amazonensis murine infection. BALB/c mice were infected with 105 amastigotes for 24 h, 3 days, 7 days, 15 days or 30 days. At different times of infection, the relative weight of the Thymus was obtained, and the Thymus cellularity was determined by counting total cells of one thymic lobe. The thymic lobe was, alternatively, processed for standard Haematoxylin and Eosin protocol. Our results suggest thymic alteration during the early days of BALB/c mice infection with L. amazonensis. The thymic hypertrophy was accompanied by histological alterations in Thymus architecture with thickening cortex at 3 days p.i. and loss of an evident delimitation between the cortex and medulla at 7 days p.i. when compared to the control mice. That is the first time that Thymus hypertrophy was observed during the early leishmaniasis. However, how it may contribute to infection susceptibility requires further investigation.

High-Oxygen Submersion Fetal Thymus Organ Cultures Enable FOXN1-Dependent and -Independent Support of T Lymphopoiesis.

T cell development is effectively supported in fetal thymus organ cultures (FTOCs), which places thymus lobes atop an air-liquid interface (ALI) culture system. The direct exposure to air is critical for its success, as fetal thymus lobes placed in low oxygen submersion (LOS)-FTOCs fail to support thymocyte development. However, submersion cultures performed in the presence of high concentration of ambient oxygen (60~80%) allow for normal thymocyte development, but the underlying mechanism for this rescue has remained elusive. Here, we show that FOXN1 expression in thymic epithelial cells (TECs) from LOS-FTOCs was greatly reduced compared to conventional ALI-FTOCs. Consequently, the expression of important FOXN1 target genes, including Dll4 and Ccl25, in TECs was extinguished. The loss of DLL4 and CCL25 interrupted thymocyte differentiation and led to CD4+CD8+ cells exiting the lobes, respectively. High oxygen submersion (HOS)-FTOCs restored the expression of FOXN1 and its target genes, as well as maintained high levels of MHCII expression in TECs. In addition, HOS-FTOCs promoted the self-renewal of CD4−CD8−CD44−CD25+ cells, allowing for the continuous generation of later stage thymocytes. Forced FOXN1 expression in TECs rescued thymocyte developmental progression, but not cellularity, in LOS-FTOCs. Given that oxidative stress has been reported to accelerate the onset of age-associated thymic involution, we postulate that regulation of FOXN1 by oxygen and antioxidants may underpin this biological process.

MACRO AND MICROSCOPIC ANATOMY PECULIARITIES OF THYMUS IN CHILDREN AND ELDERLY PEOPLE

This article is investigating macro- and microscopic anatomy peculiarities of the thymus in children and elderly people. The thymus structures and anatomical parameters studied in children of early childhood and elderly people. Anatomical methods (preparation and measurement) and histological methods (hemotoxylin-eosin staining, van-Gizon staining) have been used. The dynamics of cell populations in a unit of the conditional area of the cortical substance of the thymus lobes in children of early childhood in the city of Kara- Balta, medium, and small lymphocytes are increased. The vascular wall in some cases is thickened and sclerosed. The dynamics of cell populations in a unit of the conditional area of the cortical substance of the thymus lobes in children of early childhood in the city of Cholpon-Ata noted that lymphoblasts and small lymphocytes found in greater numbers, as well as Hassall bodies and macrophages in larger numbers.

Progress towards xenogenic tolerance.

To describe the most recent progress towards tolerance in xenotransplantation. Mixed chimerism and thymic transplantation have been used to promote tolerance in xenotransplantation models. Intra-bone bone marrow transplantation is a recent advance for mixed chimerism, which promotes longer lasting chimerism and early graft function of subsequent organ transplantation. The hybrid thymus, an advancement to the vascularized thymokidney and vascularized thymic lobe, is being developed to allow for both donor and recipient T-cell selection in the chimeric thymus, encouraging tolerance to self and donor while maintaining appropriate immune function. Regulatory T cells show promise to promote tolerance by suppressing effector T cells and by supporting mixed chimerism. Monoclonal antibodies such as anti-CD2 may promote tolerance through suppression of CD2+ effector and memory T cells whereas Tregs, which express lower numbers of CD2, are relatively spared and might be used to promote tolerance. These findings contribute major advances to tolerance in xenotransplantation. A combination of many of these mechanisms will likely be needed to have long-term tolerance maintained without the use of immunosuppression.

Histological Signs of the Thymic Enlargement

Currently, the mortality rate in pediatric population resulted from such diseases as respiratory distress syndrome, pneumonia and infections is extremely high. It cannot be ruled out that this is due to impaired functioning of the children's immune system. The thymus gland appears to be the central organ of immunopoiesis in children, that is why pediatricians pay special attention to thymic hyperplasia. To date, there is no consensus on the nature and clinical significance of the thymic enlargement. The aim of research was to study morphometric parameters of the thymus gland in children of the first year of life having thymic enlargement. Material and methods . To analyze the incidence of thymic enlargement in deceased children, the authors selected 764 autopsy protocols of children for the period from 2012 to 2017; of these, 117 were children who died in their first year of life. Autopsies were performed in Saratov Centralized Pediatric Prosectorium. The thymic enlargement in deceased children of the first year of life was detected in 34% (40 cases). Autopsy material of 32 children was selected (15 cases with and 17 cases without the thymic enlargement) for histological examination. The thymic index was calculated to specify correlation between the thymus mass and the age and body weight of a child. Morphometric studies were performed using an mVizo-103 microvisor. Results. As demonstrated, infectious diseases are a risk factor for the formation of thymomegaly in children of the first year of life. A morphological study detected that the thymic enlargement occurred mainly due to the enlargement of the cortical layer with the reduction of the lobule area. The lobule area in the studied group of children reduced by 15%, and the number of lobes bordering in the field of view increased by 50%, respectively to the similar parameters in children of the comparison group. Conclusion. Thus, infectious pathologies appear to be the most common cause of death in children with the thymic enlargement. The study results support the fact that histological signs of thymomegaly are the increased number of bordering thymic lobes in the field of view and the increased number of immature thymocytes.

The effect of different doses of probiotic feed additives on hematologic indices and morphological structure of individual pig internal organs

In order to improve the digestibility and absorption of feed, metabolic processes, growth and development of animals, increase the resistance of the body immunomodulatory agents, probiotics, prebiotics, combined enzyme-probiotic feed additives are widely used. The purpose of our work was to conduct comparative clinical trials of the effectiveness of the probiotic feed additive Probion-forte in terms of productivity, blood indices and histological structure of individual internal pigs organs during fattening. The researches were carried out on 120 piglets of big white breed at the age of 28 days, which were divided into 4 groups with 30 units in each one. The probiotics were added to feed in different concentrations in order to determine their efficiency and examine influence on piglets organism: the first group was given probiotic Probion-forte in dose of 1.0 g/kg (10 weeks); the second one – Probion in dose of 1.0 g/kg (6 weeks) and 0.5 g/kg (4 weeks); the third one was given probiotic Bio Plus 2B in dose of 0.4 g/kg for 10 weeks; and the fourth one was a control group. The compound feed was provided according to norms recommended for big white breed taking into account age. On the 42nd day (6 weeks) and on the 70th day of test 10 units were selected for haematological, pathomorphological and microbiological tests. The productivity of animals of all studied groups was evaluated by the average daily gains, safety, feed conversion and slaughter output. The stabilized with EDTA piglets’ blood was used for morphological studies, and blood serum – for biochemical studies. The clinical trials have shown that the application of Probion-forte, as a feed additive for fattening of piglets within 10 weeks after weaning, did not cause adverse reactions, was well tolerated by animals and contributed to the improvement of the processes of erythropoiesis and leucopoiesis, increased of serum total protein content. The increasing activity of serum transaminases indicated more intense metabolic processes in experimental animals’ organism, which was confirmed by increase in average daily weight gains and slaughter output compared to control. In the microscopic examination of the thymus, spleen, lymph nodes, intestines, liver, the characteristic histological structure of the organs was preserved and indicated their active morphofunctional state throughout the study period. Morphometrically the increase in the height of the villi in the duodenum and the size of the thymus lobes in piglets, which were fed with probiotic feed additives was established. The efficiency and appropriateness of the application of these products was confirmed in the first and second experimental groups. However, the most significant difference was observed in piglets fed with Probion-forte for 10 weeks at a dose of 1.0 g/kg of feed.