Severe gut mucosal injury induces profound systemic inflammation and spleen-associated lymphoid organ response

Clinical evidence indicates a connection between gut injuries, infections, inflammation, and an increased susceptibility to systemic inflammation. Nevertheless, the animal models designed to replicate this progression are inadequate, and the fundamental mechanisms are still largely unknown. This research explores the relationship between gut injuries and systemic inflammation using a Dextran Sulfate Sodium (DSS)-induced colonic mucosal injury mouse model. Continuous treatment of adult mice with 4% DSS drinking water yielded a remarkable mortality rate by day 7, alongside intensified gut injury and detectable peripheral inflammation. Moreover, RNAscope in situ hybridization with 16S rRNA probe noted bacterial penetration into deeper colon compartments of the mice following treatment with DSS for 7 days. Histological analysis revealed inflammation in the liver and lung tissues of DSS-treated mice. In addition, we found that DSS-treated mice exhibited elevation of Alanine transaminase (ALT) and Aspartate transaminase (AST) in peripheral blood and pro-inflammatory cytokine levels in the liver. Notably, the DSS-treated mice displayed a dampened metabolic profile, reduced CD45 marker expression, and an increase in apoptosis within the lymphoid organ such as spleen. These findings suggest that high-dose DSS-induced gut injury gives rise to sepsis-like systemic inflammation characterized by multiple organ injury and profound splenocyte apoptosis and dysfunction of CD45+ cells in the spleen, indicating the role of the spleen in the pathogenesis of gut-derived systemic inflammation. Together, the severe colonic mucosal injury model facilitates research into gut damage and associated peripheral immune responses, providing a vital framework for investigating mechanisms related to clinically relevant, gut-derived systemic inflammation.

mRNA vaccine designs for optimal adjuvanticity and delivery

Adjuvanticity and delivery are crucial facets of mRNA vaccine design. In modern mRNA vaccines, adjuvant functions are integrated into mRNA vaccine nanoparticles, allowing the co-delivery of antigen mRNA and adjuvants in a unified, all-in-one formulation. In this formulation, many mRNA vaccines utilize the immunostimulating properties of mRNA and vaccine carrier components, including lipids and polymers, as adjuvants. However, careful design is necessary, as excessive adjuvanticity and activation of improper innate immune signalling can conversely hinder vaccination efficacy and trigger adverse effects. mRNA vaccines also require delivery systems to achieve antigen expression in antigen-presenting cells (APCs) within lymphoid organs. Some vaccines directly target APCs in the lymphoid organs, while others rely on APCs migration to the draining lymph nodes after taking up mRNA vaccines. This review explores the current mechanistic understanding of these processes and the ongoing efforts to improve vaccine safety and efficacy based on this understanding.

A Novel TRIM9 Protein Promotes NF-κB Activation Through Interacting With LvIMD in Shrimp During WSSV Infection

The TRIpartite Motif (TRIM) proteins play key roles in cell differentiation, apoptosis, development, autophagy, and innate immunity in vertebrates. In the present study, a novel TRIM9 homolog (designated as LvTRIM9-1) specifically expressed in the lymphoid organ of shrimp was identified from the Pacific whiteleg shrimp Litopenaeus vannamei. Its deduced amino acid sequence possesses the typical features of TRIM proteins, including a RING domain, two B-boxes, a coiled-coil domain, a FN3 domain, and a SPRY domain. The transcripts of LvTRIM9-1 were mainly located in the lymphoid tubules of the lymphoid organ. Knockdown of LvTRIM9-1 could apparently inhibit the transcriptions of some genes from white spot syndrome virus (WSSV) and reduce the viral propagation in the lymphoid organ. Overexpression of LvTRIM9-1 in mammalian cells could activate the promoter activity of NF-κB, and an in vivo experiment in shrimp showed that knockdown of LvTRIM9-1 reduced the expression of LvRelish in the lymphoid organ. Yeast two-hybridization and co-immunoprecipitation (Co-IP) assays confirmed that LvTRIM9-1 could directly interact with LvIMD, a key component of the IMD pathway, through its SPRY domain. These data suggest that LvTRIM9-1 could activate the IMD pathway in shrimp via interaction with LvIMD. This is the first evidence to show the regulation of a TRIM9 protein on the IMD pathway through its direct interaction with IMD, which will enrich our knowledge on the role of TRIM proteins in innate immunity of invertebrates.

Cytological, Histochemical, and Ultrastructural Study of the Human Fetal Spleen of Various Gestational Age With Future Implications in Splenic Transplantation: An Anatomical Perspective

Purpose: The spleen is a fist-sized largest lymphoid organ located in the left hypochondrium. It has a unique location, embryological and histological structure that differs significantly from other lymphoid organs. The present work was undertaken to study the microscopic and ultramicroscopic histogenesis patterns of the spleen in relation to gestational age.

Methods: The splenic tissue of nine aborted fetuses of various gestational ages was studied. For cytology study, special stains like Masson’s trichrome, Periodic Acid-Schiff, and Reticulin were used; immunohistochemical staining was performed with triple antibodies (C-myc, Ki-67, and Ber-H2); and for ultrastructure study, aluminum mounted specimens coated with gold and argon gas were observed under scanning electron microscopy (SEM).

Results: Microscopy and immunohistochemistry showed the developmental changes in the spleen from the emergence of the primordium to the end of the embryonic period in all stages of fetogenesis. The spleen primordium of a fetus at the developmental stage of the primary vascular reticulum was seen in the first trimester fetuses. The primordium is comprised mainly of mesenchymal tissue; numerous lymphocytes invading the area surrounding the central artery forming the periarterial lymphoid sheaths (PALS) were seen surrounded by venous sinuses in the early second trimester fetuses.

Conclusion: The organizational changes in the reticuloendothelial system and microstructure of the spleen during fetogenesis are very crucial to achieving adult morphology in the future. Histogenesis of the fetal spleen follows a multistep process depending upon the gestational age. Any deviation from normalcy may lead to structural and functional abnormality later in life.

Different Immune Responses of the Lymphoid Organ in Shrimp at Early Challenge Stage of Vibrio parahaemolyticus and WSSV

Simple Summary

Disease is a frequently encountered problem in aquaculture, which always causes global economic losses. White spot syndrome virus (WSSV) and Vibrio parahaemolyticus are two of the most destructive pathogens causing severe loss of shrimp aquaculture. Understanding the host immune responses against different pathogens is vital for developing effective disease control technologies. The lymphoid organ is a vital part of the shrimp immune system and exhibits important immune functions including cellular and humoral immunity. However, the immune function of the lymphoid organ and its responses against different pathogens are still largely unclear. In the present study, transcriptomic analysis was applied to compare the differentially expressed genes (DEGs) in the lymphoid organ of shrimp after Vibrio or WSSV challenge. Data showed that Vibrio challenge induced broad immune responses in the lymphoid organ including activation of several pattern recognition receptors, the proPO activating system, phagocytosis related genes, and immune effectors. In contrast, the immune responses seemed to be inhibited after WSSV infection. The present study suggests that the shrimp lymphoid organ plays different functions in response to the infection of distinct pathogens at early stage, which provides new insights into the immune functions of lymphoid organ in shrimp.

Abstract

The lymphoid organ is an essential part of the immune system involved in cellular and humoral immune responses in shrimp. However, its roles in the immune responses against different pathogens are still largely unclear. In the present study, transcriptomic analysis was applied to compare the differentially expressed genes (DEGs) in the lymphoid organ of shrimp after Vibrio or WSSV challenge. In total, 2127 DEGs were screened in the lymphoid organ of shrimp at 6 h post Vibrio parahaemolyticus injection, and 1569 DEGs were obtained at the same time after WSSV challenge. KEGG pathway enrichment analysis of these DEGs revealed that two significantly enriched pathways including “neuroactive ligand–receptor interaction” and “protein digestion and absorption” were responsive to both pathogens. In contrast, “lysosome” was the significantly enriched pathway only in Vibrio challenge whereas carbohydrate metabolism related pathways were the significantly enriched pathways only in WSSV challenge. Further analysis on immune-related DEGs showed that Vibrio challenge induced broad immune responses in the lymphoid organ including activation of several pattern recognition receptors, the proPO activating system, phagocytosis related genes, and immune effectors. In contrast, the immune responses seemed to be inhibited after WSSV infection. The data suggest that the shrimp lymphoid organ plays different functions in response to the infection of distinct pathogens at the early stage, which provides new insights into the immune functions of lymphoid organ in shrimp.

A Lymphoid Organ Specific Anti-Lipopolysaccharide Factor from Litopenaeus vannamei Exhibits Strong Antimicrobial Activities

Different shrimp species are known to possess apparent distinct resistance to different pathogens in aquaculture. However, the molecular mechanism underlying this finding still remains unknown. One kind of important antimicrobial peptides, anti-lipopolysaccharide factors (ALF), exhibit broad-spectrum antimicrobial activities. Here, we reported a newly identified ALF from the shrimp Litopenaeus vannamei and compared the immune function with its counterpart in the shrimp Fenneropenaeus chinensis. The ALF, designated as LvALF8, was specifically expressed in the lymphoid organ of L. vannamei. The expression level of LvALF8 was apparently changed after white spot syndrome virus (WSSV) or Vibrio parahaemolyticus challenges. The synthetic LBD peptide of LvALF8 (LvALF8-LBD) showed strong antibacterial activities against most tested Gram-negative and Gram-positive bacteria. LvALF8-LBD could also inhibit the in vivo propagation of WSSV similar as FcALF8-LBD, the LBD of LvALF8 counterpart in F. chinensis. However, LvALF8-LBD and FcALF8-LBD exhibited apparently different antibacterial activity against V. parahaemolyticus, the main pathogen causing acute hepatopancreatic necrosis disease (AHPND) of affected shrimp. A structural analysis showed that the positive net charge and amphipathicity characteristics of LvALF8-LBD peptide were speculated as two important components for its enhanced antimicrobial activity compared to those of FcALF8-LBD. These new findings may not only provide some evidence to explain the distinct disease resistance among different shrimp species, but also lay out new research ground for the testing and development of LBD-originated antimicrobial peptides to control of shrimp diseases.

Distinct Distribution of RTN1A in Immune Cells in Mouse Skin and Lymphoid Organs

The endoplasmic reticulum-associated protein reticulon 1A (RTN1A) is primarily expressed in neuronal tissues but was recently identified also specifically in cells of the dendritic cell (DC) lineage, including epidermal Langerhans cells (LCs) and dermal DCs in human skin. In this study, we found that in mice major histocompatibility complex class II (MHCII)⁺CD207⁺ LCs but not dermal DCs express RTN1A. Further, RTN1A expression was identified in CD45⁺MHCII⁺CD207⁺ cells of the lymph node and spleen but not in the thymus. Of note, RTN1A was expressed in CD207^low LCs in adult skin as well as emigrated LCs and DCs in lymph nodes and marginally in CD207^hi cells. Ontogeny studies revealed that RTN1A expression occurred before the appearance of the LC markers MHCII and CD207 in LC precursors, while dermal DC and T cell precursors remained negative during skin development. Analogous to the expression of RTN1A in neural tissue, we identified expression of RTN1A in skin nerves. Immunostaining revealed co-localization of RTN1A with nerve neurofilaments only in fetal but not in newborn or adult dermis. Our findings suggest that RTN1A might be involved in the LC differentiation process given its early expression in LC precursors and stable expression onward. Further analysis of the RTN1A expression pattern will enable the elucidation of the functional roles of RTN1A in both the immune and the nervous system of the skin.

Immunodepression induced by influenza A virus (H1N1) in lymphoid organs functions as a pathogenic mechanism

In recent years, the frequency of influenza epidemics around the world has posed a great threat to the lives of people, especially those in developing countries. However, it is unclear which organs are the targets of influenza A viruses (IAVs) and what histopathology is caused by IAVs. In this study, BALB/c female mice were infected with H1N1 by nasal inoculation for 5 days. After euthanasia, the brain, heart, lungs, thymus, liver, spleen, hilar lymph nodes, pancreas, kidneys, and adrenal glands were collected. Among these organs, only the lungs, thymus, spleen, and hilar lymph nodes showed lesions. Lung histopathology was characterized by widening of the septum, lymphocyte infiltration, alveolar effusion, and alveolar hyaline membrane formation. The thymus and spleen exhibited atrophy due to the apoptosis of numerous lymphocytes. Although the hilar lymph nodes were enlarged, lymphocyte apoptosis still occurred. The nucleocapsid protein (NP) of IAVs was present not only in the lungs but also in the thymus, spleen, and hilar lymph nodes. In peripheral blood, CD19⁺ B lymphocyte levels clearly decreased whileCD3⁺ CD8⁺ T and CD3⁺ CD4⁺ T lymphocyte levels temporarily decreased but subsequently increased. These results demonstrate that H1N1 in the lungs could reach lymphoid organs, induce the depletion of B and T lymphocytes in peripheral blood and lymphoid organs, and suppress adaptive immunity.

Characterization of a Lymphoid Organ Specific Anti-lipopolysaccharide Factor From Shrimp Reveals Structure-Activity Relationship of the LPS-Binding Domain

Anti-lipopolysaccharide factor (ALF) is a kind of important antimicrobial peptides with broad-spectrum antimicrobial activities. The LPS-binding domain (LBD) contributes to the major antimicrobial activity of ALF. However, LBDs from different ALFs share low sequence similarity. The general character of LBDs needs to be elucidated to understand the molecular mechanism of their function and facilitate LBD-original drug design. Here we identified a lymphoid organ specifically expressed ALF, designated as FcALF8, from the Chinese shrimp Fenneropenaeus chinensis. The synthetic LBD peptide of FcALF8 (LBD8) showed strong antibacterial activities to the pathogenic Vibrio, such as Vibrio alginolyticus, Vibrio harveyi, and Photobacterium damselae with a MIC value of 0.5–1, 1–2, and 1–2 μM, respectively. FcALF8 knock-down using dsRNA led to significant increase of the viable bacteria in the lymphoid organ and hepatopancreas of shrimp upon V. harveyi infection. On the contrary, the proliferation of V. harveyi in the shrimp lymphoid organ and hepatopancreas significantly decreased after infected by LBD8 pre-incubated V. harveyi. Sequence alignments showed that the LBDs from 39 ALFs shared only two identical cysteine residues. However, 17 of the total 22 LBD residues showed high similarity when the amino acids were classified into hydrophobic and hydrophilic ones. A further activity analysis on modified LBD8 peptides showed that the antibacterial activity of LBD8 was lost after linearization and apparently weakened after changing the amino acid property at certain positions. The data indicated that the disulfide bond and amino acid property contributed to the conservation of the functional domain. To the best of our knowledge, this is the first identified ALFs specifically expressed in the lymphoid organ of shrimp with strong antibacterial activity. The present data will give creative instructions for the design of LBD-originated antimicrobial agents.

A Single-Cell Transcriptomic Atlas of Thymus Organogenesis Resolves Cell Types and Developmental Maturation

Thymus development is critical to the adaptive immune system, yet a comprehensive transcriptional framework capturing thymus organogenesis at single-cell resolution is still needed. We applied single-cell RNA sequencing (RNA-seq) to capture 8 days of thymus development, perturbations of T cell receptor rearrangement, and in vitro organ cultures, producing profiles of 24,279 cells. We resolved transcriptional heterogeneity of developing lymphocytes, and genetic perturbation confirmed T cell identity of conventional and non-conventional lymphocytes. We characterized maturation dynamics of thymic epithelial cells in vivo, classified cell maturation state in a thymic organ culture, and revealed the intrinsic capacity of thymic epithelium to preserve transcriptional regularity despite exposure to exogenous retinoic acid. Finally, by integrating the cell atlas with human genome-wide association study (GWAS) data and autoimmune-disease-related genes, we implicated embryonic thymus-resident cells as possible participants in autoimmune disease etiologies. This resource provides a single-cell transcriptional framework for biological discovery and molecular analysis of thymus organogenesis.

Origin and evolution of adaptive immunity

The evolutionary emergence of vertebrates was accompanied by major morphological and functional innovations, including the development of an adaptive immune system. Vertebrate adaptive immunity is based on the clonal expression of somatically diversifying antigen receptors on lymphocytes. This is a common feature of both the jawless and jawed vertebrates , although these two groups of extant vertebrates employ structurally different types of antigen receptors and principal mechanisms for their somatic diversification . These observations suggest that the common vertebrate ancestor must have already possessed a complex immune system, including B- and T-like lymphocyte lineages and primary lymphoid organs, such as the thymus, but possibly lacked the facilities for somatic diversification of antigen receptors. Interestingly, memory formation, previously considered to be a defining feature of adaptive immunity, also occurs in the context of innate immune responses and can even be observed in unicellular organisms, attesting to the convergent evolutionary history of distinct aspects of adaptive immunity.

The distribution of T lymphocytes, B lymphocytes, and dendritic-like cells of the anal tonsil in the laboratory shrew, Suncus murinus

We investigated the distribution of T lymphocytes, B lymphocytes, and S-100 protein-immunoreactive dendritic-like in the anal tonsil of the laboratory shrew, Suncus murinus. In adult animals, T lymphocytes were located mainly at the periphery of the anal tonsil, especially around small blood vessels. B lymphocytes were located in the central and subepithelial region of the anal tonsil, which includes primary lymphoid follicles, and in which there are small numbers of scattered T lymphocytes. B and T lymphocytes were distributed over 72.7 and 27.3% of the tonsillar area, respectively. However, their areas of distribution were not clearly distinguished. The areas containing B lymphocytes were enriched in S-100 protein antibody-immunoreactive cells, which exhibited a dendritic shape. These S-100-positive cells appeared to be identical to the follicular dendritic cells (FDC) seen in the follicles of lymphoid organs. These results suggest that the anal tonsils constitute one of the gut-associated lymphoid tissues (GALT), and that a function of the anal tonsil includes the capture of intruding antigens that would generate protective antibody responses.

Low viral loads and lymphoid organ spheroids are associated with yellow head virus (YHV) tolerance in whiteleg shrimp Penaeus vannamei

Yellow head virus (YHV) is an invertebrate nidovirus that has caused mass mortality in penaeid shrimp since 1990. Several YHV types are known, but only the original type (YHV-type 1 or YHV-1) is highly virulent. Most studies have focused on acute YHV-1 infections and there is limited work on YHV-1 survivors. We compared moribund and surviving (14%) whiteleg shrimp Penaeus (Litopenaeus) vannamei from an experimental challenge with YHV-1. Although grossly normal, all survivors were positive for YHV-1 by specific, reverse transcriptase polymerase chain reaction (RT-PCR) assays, histological analysis or transmission electron microscopy (TEM), indicating that they were not resistant but tolerant to YHV-1. On the other hand, real-time PCR analysis revealed that mean YHV-1 copies/ng total RNA for survivors (2.8x10(4) +/- 6.9x10(4)) were approximately 40 times lower (P<0.05) than those in moribund shrimp (1.2x10(6) +/- 6.7x10(5)copies/ng total RNA). This was confirmed by strong positive immunohistochemical and in situ hybridization (ISH) reactions for YHV-1 in lymphoid organ tubules (LOT) of moribund shrimp and weak positive reaction only in lymphoid organ spheroids (LOS) of survivors. TEM revealed morphologically complete YHV virions in both groups. Furthermore, immuno-TEM and Western blot analysis revealed that YHV-1 structural proteins gp116 and p20 were present at comparable reactive levels in each group. Thus, YHV-1 tolerance was not associated with absence of gp116 as previously reported for palaemonid shrimp. Instead, it was associated with the presence of YHV-positive LOS and a relatively low viral load.

Transgenic LacZ under control of Hec-6st regulatory sequences recapitulates endogenous gene expression on high endothelial venules

Hec-6st is a highly specific high endothelial venule (HEV) gene that is crucial for regulating lymphocyte homing to lymph nodes (LN). The enzyme is also expressed in HEV-like vessels in tertiary lymphoid organs that form in chronic inflammation in autoimmunity, graft rejection, and microbial infection. Understanding the molecular nature of Hec-6st regulation is crucial for elucidating its function in development and disease. However, studies of HEV are limited because of the difficulties in isolating and maintaining the unique characteristics of these vessels in vitro. The novel pClasper yeast homologous recombination technique was used to isolate from a BAC clone a 60-kb DNA fragment that included the Hec-6st (Chst4) gene with flanking sequences. Transgenic mice were generated with the beta-galactosidase (LacZ) reporter gene inserted in-frame in the exon II of Hec-6st within the isolated BAC DNA fragment. LacZ was expressed specifically on HEV in LN, as indicated by its colocalization with peripheral node vascular addressin. LacZ was increased in nasal-associated lymphoid tissue during development and was reduced in LN and nasal-associated lymphoid tissue by LTbetaR-Ig (lymphotoxin-beta receptor human Ig fusion protein) treatment in a manner identical to the endogenous gene. The transgene was expressed at high levels in lymphoid accumulations with characteristics of tertiary lymphoid organs in the salivary glands of aged mice. Thus, the Hec-6s-LacZ construct faithfully reproduces Hec-6st tissue-specific expression and can be used in further studies to drive expression of reporter or effector genes, which could visualize or inhibit HEV in autoimmunity.

Derangement of immune responses by myeloid suppressor cells

In tumor-bearing mice and cancer patients, tumor progression is often associated with altered hematopoiesis leading to the accumulation of myeloid cells. Extensive studies in preclinical models indicate that these cells share the CD11b and the Gr-1 markers, possess a mixed mature-immature myeloid phenotype, and are responsible for the induction of T-cell dysfunctions, both tumor-specific and nonspecific. Moreover, CD11b(+)Gr-1(+) myeloid cells are described under different unrelated situations associated with temporary impairment of the T-lymphocyte reactivity. This review examines recent findings on the nature, properties, and mechanisms of action of these myeloid suppressor cells (MSCs).

Chemokine requirements for B cell entry to lymph nodes and Peyer's patches

B cell entry to lymph nodes and Peyer's patches depends on chemokine receptor signaling, but the principal chemokine involved has not been defined. Here we show that the homing of CXCR4-/- B cells is suppressed in CCL19 (ELC)- and CCL21 (SLC)-deficient paucity of lymph node T cells mice, but not in wild-type mice. We also find that CXCR4 can contribute to T cell homing. Using intravital microscopy, we find that B cell adhesion to high endothelial venules (HEVs) is disrupted when CCR7 and CXCR4 are predesensitized. In Peyer's patches, B cell entry is dependent on CXCR5 in addition to CCR7/CXCR4. CXCL12 (SDF1) is displayed broadly on HEVs, whereas CXCL13 (BLC) is found selectively on Peyer's patch follicular HEVs. These findings establish the principal chemokine and chemokine receptor requirements for B cell entry to lymph nodes and Peyer's patches.