Evolution of immune defence responses as incremental layers among Metazoa

Transcriptome profiling of microdissected cortex and medulla unravels functional regionalization in the European sea bass Dicentrarchus labrax thymus

The thymus is a sophisticated primary lymphoid organ in jawed vertebrates, but knowledge on teleost thymus remains scarce. In this study, for the first time in the European sea bass, laser capture microdissection was leveraged to collect two thymic regions based on histological features, namely the cortex and the medulla. The two regions were then processed by RNAseq and in-depth functional transcriptome analyses with the aim of revealing differential gene expression patterns and gene sets enrichments, ultimately unraveling unique microenvironments imperative for the development of functional T cells. The sea bass cortex emerged as a hub of T cell commitment, somatic recombination, chromatin remodeling, cell cycle regulation, and presentation of self antigens from autophagy-, proteasome- or proteases-processed proteins. The cortex therefore accommodated extensive thymocyte proliferation and differentiation up to the checkpoint of positive selection. The medulla instead appeared as the center stage in autoimmune regulation by negative selection and deletion of autoreactive T cells, central tolerance mechanisms and extracellular matrix organization. Region-specific canonical markers of T and non-T lineage cells as well as signals for migration to/from, and trafficking within, the thymus were identified, shedding light on the highly coordinated and exquisitely complex bi-directional interactions among thymocytes and stromal components. Markers ascribable to thymic nurse cells and poorly characterized post-aire mTEC populations were found in the cortex and medulla, respectively. An in-depth data mining also exposed previously un-annotated genomic resources with differential signatures. Overall, our findings contribute to a broader understanding of the relationship between regional organization and function in the European sea bass thymus, and provide essential insights into the molecular mechanisms underlying T-cell mediated adaptive immune responses in teleosts.

Cellular and humoral immune response between snail hosts and their parasites

In invertebrates, the innate immune system protects against a wide range of microbiological infections. Several immunological processes are involved in the interactive immune response between snails and their parasites, including phagocytosis, nitric oxide synthesis, phenol oxidase activity, lysozymes, and lectin formation. The immunological responses connected to the interaction between snails and parasites are discussed in detail in the current research. Understanding the nature of these interactive reactions will enable scientists to explore approaches to eliminate and cure parasitic infections.

A novel C-type lectin LvCTL 4.2 has antibacterial activity but facilitates WSSV infection in shrimp (L. vannamei)

Glycan-binding protein C-type lectin (CTL), one of the pattern recognition receptors (PRRs), binds to carbohydrates on the surface of pathogens and elicits antimicrobial responses in shrimp innate immunity. The objective was to identify and characterize a novel C-type lectin LvCTL 4.2 in Litopenaeus vannamei. The LvCTL 4.2 protein consisted of a signal peptide at the N terminal and a carbohydrate-recognition domain (CRD) with a mutated mannose-binding (Glu-Pro-Ala; EPA) motif at the C terminal, and thereby has a putative secreted mannose-binding C-type lectin architecture. LvCTL 4.2 was highly expressed in nervous tissue and stomach. Infection with white spot syndrome virus (WSSV) induced expression of LvCTL 4.2 in shrimp stomach at 12 h post infection. Conversely, there was no obvious upregulation in expression of LvCTL 4.2 in stomach or hepatopancreas of shrimp with AHPND (acute hepatopancreas necrosis disease). Pathogen binding assays confirmed recombinant LvCTL 4.2 protein (rLvCTL 4.2) had significant binding ability with the WSSV virion, Gram-negative, and Gram-positive bacteria. Moreover, rLvCTL 4.2 had strong growth inhibition of Vibrio parahaemolyticus. Silencing LvCTL 4.2 suppressed WSSV replication, whereas pretreatment of WSSV with rLvCTL 4.2 facilitated viral replication in vivo. In conclusion, LvCTL 4.2 acted as a PRR that inhibited AHPND-causing bacteria, but facilitated WSSV pathogenesis.

Comparative transcriptome profiling of horseshoe crab Tachypleus gigas hemocytes in response to lipopolysaccharides

Horseshoe crabs (HSCs) are living fossil species of marine arthropods with a long evolutionary history spanning approximately 500 million years. Their survival is helped by their innate immune system that comprises cellular and humoral immune components to protect them against invading pathogens. To help understand the genetic mechanisms involved, the present study utilised the Illumina HiSeq platform to perform transcriptomic analysis of hemocytes from the HSC, Tachypleus gigas, that were challenged with lipopolysaccharides (LPS). The high-throughput sequencing resulted in 352,077,208 and 386,749,136 raw reads corresponding to 282,490,910 and 305,709,830 high-quality mappable reads for the control and LPS-treated hemocyte samples, respectively. Based on the log-fold change of > 0.3 or < -0.3, 1338 genes were significantly upregulated and 215 genes were significantly downregulated following LPS stimulation. The differentially expressed genes (DEGs) were further identified to be associated with multiple pathways such as those related to immune defence, stress response, cytoskeleton function and signal transduction. This study provides insights into the underlying molecular and regulatory mechanisms in hemocytes exposed to LPS, which has relevance for the study of the immune response of HSCs to infection.