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Hemocytes play vital roles in the immune response. Despite progress in the characterization of molluscan hemocytes and immune cells, including their cellular receptors and signal transduction pathways, the processes that lead to their differentiation in bivalve larvae remain unknown. Furthermore, the molecular mechanisms of that decide hemocyte stem cell fate and self-renewal during development remain poorly characterized. Similar to adult mollusks, the larvae are filter feeders and are highly susceptible to pathogens and biotoxins; therefore, it is important to understand the development and function of their immune system. This review summarizes the current data on the appearance of elements of the immune system in bivalve larvae. I have discussed why the immune cells emerge before the circular blood vessel system, which differentiates at the late stages of development. I also discuss how molluscan hemocytes are involved in the development of disseminated neoplasia., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Our understanding of how equine immunoglobulin genes are organized has increased significantly in recent years. For equine heavy chains, 52 IGHV, 40 IGHD, 8 IGHJ and 11 IGHC are present. Seven of these IGHCs are gamma chain genes. Sequence diversity is increasing between fetal, neonatal, foal and adult age. The kappa light chain contains 60 IGKV, 5 IGKJ and 1 IGKC, whereas there are 144 IGLV, 7 IGLJ, and 7 IGLC for the lambda light chain, which is expressed predominantly in horses. Significant transcriptional differences for IGLV and IGLC are identified in different breeds. Allotypic and allelic variants are observed for IGLC1, IGLC5, and IGLC6/7, and two IGLV pseudogenes are also transcribed. During age development, a decrease in IGLVs is noted, although nucleotide diversity and significant differences in gene usage increased. The following paper suggests a standardization of the existing nomenclature of immunoglobulin genes., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Sturgeon aquaculture has increased considerably worldwide but little is known about their immunological development and competence in early life stages. Culture of larvae is one of the most critical stages in intensive sturgeon farming, often associated with high mortality rates. The objective of this study was to characterize the developmental morphology (light and transmission electron microscopy, LM and TEM) of the meningeal myeloid tissue, spleen and thymus in Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus) from hatching until 5 months old (2895°C·day (dd)). The spleen was first visible on 541 dd larvae LM sections and the other two immune organs in 768 dd samples (approximately 400 and 600 dd after onset of feeding). Generally, younger fish had significantly higher percentages of undifferentiated cells (meningeal myeloid tissue and spleen) and effective adaptive immune competence would not be expected in these fish on the onset of feeding, but further functional immune assessment is needed., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

The current review focuses on pre- and post-natal development of intestinal immunoglobulin A (IgA) production in pig. IgA production is influenced by intrinsic genetic factors in the foetus as well as extrinsic environmental factors during the post-natal period. At birth, piglets are exposed to new antigens through maternal colostrums/milk as well as exogenous microbiota. This exposure to new antigens is critical for the proper development of the gut mucosal immune system and is characterized mainly by the establishment of IgA response. A second critical period for neonatal intestinal immune system development occurs at weaning time when the gut environment is exposed to new dietary antigens. Neonate needs to establish oral tolerance and in the absence of protective milk need to fight potential new pathogens. To improve knowledge about the immune response in the neonates, it is important to identify intrinsic and extrinsic factors which influence the intestinal immune system development and to elucidate their mechanism of action., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

A full length cDNA sequence expressed in coelomocytes shows significant sequence match to vertebrate Tie1 and Tie2/TEK. Vertebrate Tie2/TEK is the receptor for the angiopoietins and plays an important role in angiogenesis and hematopoiesis, whereas Tie1 regulates the activity of Tie2. The deduced sequence of the SpTie1/2 protein has a similar order and organization of domains to the homologous vertebrate proteins including a highly conserved receptor tyrosine kinase domain in the cytoplasmic tail. The N terminus of the ectodomain has one immunoglobulin (Ig)-Tie2_1 domain, followed by an Ig domain, four epidermal growth factor domains, a second Ig domain, and three fibronectin type III domains. The SpTie1/2 gene is expressed in coelomocytes and the axial organ, whereas other organs do not show significant expression. The timing of embryonic expression corresponds with the differentiation of blastocoelar cells, the embryonic and larval immune cells. Searches of the sea urchin genome show several gene models encoding putative ligands and signaling proteins that might interact with SpTie1/2. We speculate that SpTie1/2 may be involved in the proliferation of sea urchin immune cells in both adults and embryos., (Copyright 2010 Elsevier Ltd. All rights reserved.)

The immune system in teleosts is not completely developed during embryonic and larval stages and immune competence is assumed to be restricted. This study is the first to address whether immune transcripts are maternally transferred to offspring and when immune genes are transcriptionally active in Atlantic cod (Gadus morhua). In unfertilised eggs, transcripts encoding lysozyme and cathelicidin were found indicating maternal transfer of antibacterial transcripts. Lysozyme activity was also present at this stage suggesting the presence of a functional protein. Transcripts of two other putative antibacterial genes (hepcidin and pentraxin) and antiviral genes (ISG15 and LGP2) were absent in unfertilised eggs. The transcriptional onset of these genes occurred during the gastrula period. Transcripts of the heavy chain constant regions of the immunoglobulin (Ig) D, membrane-associated and secreted form of IgM were absent in unfertilised eggs. Transcription of the heavy chain locus commenced at low levels during the segmentation period indicating the onset of B-cell development. Most innate immune genes showed an increase in transcription around hatch and first feeding, indicating a preparation for increased pathogen exposure at this time. Prior to and during metamorphosis all genes showed a pronounced elevation in transcript levels indicating a further maturation of the immune system during this period.

Cellular and humoral aspects of the immune response develop sequentially in the fetus. During the ontogeny, the pluripotent stem cells emerge and differentiate into all hematopoietic lineages. Basic questions including the identification of the first lympho-hematopoietic sites, the origin of T and B lymphocytes, the development of different subpopulations of alphabeta T, gammadelta T and B lymphocytes as well as development of innate immunity and the acquisition of full immunological capacities are discussed here for swine and compared with other species. The description of related topics such as fertilization, morphogenesis, maternal-fetal-neonatal physiology and early neonatal development are also discussed.

The 'immunocompetence handicap hypothesis' predicts that highly sexually dimorphic and polygynous species will exhibit sex differences in immunity. We tested this hypothesis in southern elephant and grey seals during their early development by measuring the following parameters: leucocyte counts, serum IgG levels, erythrocyte sedimentation rate and haematocrit. We failed to find any differences due to sex as assessed by the parameters investigated. Animals were sampled longitudinally during their development and there were significant age effects from birth to weaning in both species. Total and differential leucocyte counts and erythrocyte sedimentation rates increased just prior to weaning then decreased. Haematocrits declined whilst total circulating immunoglobulin G concentrations increased. Body temperatures remained constant throughout the postnatal period. Differences between the species were seen in total leucocyte counts and in polymorphonuclear cells and eosinophils. Southern elephant seals had higher concentrations than grey seals and total leucocyte counts in the former were among the highest reported for mammals.

This paper reviews several aspects of the development of the hematopoietic and lymphoid systems in Xenopus. The developmental biology of hematopoietic stem cells and the early development of the thymus and B-cells are discussed. Recent advances in the development of molecular indices of the hematopoietic program are also considered. Previous studies as well as new data demonstrate that the hematopoietic program is initiated at the time of gastrulation. Recent advances suggest that both positive and negative regulation is necessary for the appropriate spatial and temporal expression of the hematopoietic program during development.

Spleens from larval and adult South African clawed frogs (Xenopus laevis) were examined using sucrose-potassium phosphate-glyoxylic acid (SPG) histofluorescence for norepinephrine. Innervation of the larval Xenopus spleen is barely detectable at stage 54 and gradually increases during prometamorphosis (stage 57/58) until metamorphic climax (stage 66). This development of innervation late in the larval life of the animal was highly sensitive to environmental conditions and to rapidity at which development occurred. Prevention of overt metamorphosis by sodium perchlorate blockade prevented the development of noradrenergic (NA) splenic innervation in some, but not all, tadpoles examined. Depletion of T-lymphocytes by early larval thymectomy did not alter the kinetics or pattern of splenic NA innervation.

Murine T cells bearing the gamma delta T-cell receptor (gamma delta TCR) are the major lymphocyte subset in the thymus early in fetal development, and postnatally they are the major population of T cells in the epithelia of nonlymphoid tissues including the intestine, skin, tongue, lung, and reproductive organs. The site of origin of gamma delta T-cell precursors (pre-T cells) changes during fetal development, reflecting the sites of active hematopoiesis. In addition, the pattern of expression of specific gamma delta TCR variable (V) region genes changes during fetal and neonatal development, and is unique in different epithelial tissues postnatally. We herein review the literature describing these developmental changes and provide a model for the developmental pathways of murine gamma delta T cells.

Previous studies on the morphology of the lymphomyeloid tissues in the dogfish, Scyliorhinus canicula, have been confined to adults. This study was restricted to the structure and functioning of the developing immune system in embryonic and post-hatch dogfish. A major feature of the developing immune system in S. canicula, is the succession of haemopoietic/lymphoid tissues. The liver is the first tissue to contain immunoglobulin positive cells at 2 months, followed by the interstitial kidney at 3 months. The thymus, spleen, and Leydig organ appears at 4 months while the epigonal and gut-associated lymphomyeloid tissues are the last tissues to differentiate. The haemopoietic/lymphoid nature of the kidney and thymus disappear at post-hatch and the other lymphomyeloid tissues persist through adult life. By the time of egg case splitting (ca. 6 months), when embryos receive massive exposure to water-borne antigens, the structural development of most of the lymphomyeloid tissues is well advanced.

To study the ontogeny of lymphocytes in the lizard, Chalcides ocellatus antisera were raised in rabbits against thymocytes collected from adult lizards (AATS) or from embryos of stages 40 and 41 (AETS), and against serum immunoglobulins (AGGS). AATS recognized in adult lizards a surface membrane antigenic system (TA) specific to thymocytes and thymus-derived (T-) cells in spleen, and a distinct antigenic entity (Tt) found exclusively on intrathymic lymphocytes. After exhaustive absorption with adult thymocytes, AETS defined a further antigen (TE). On the other hand, AGGS combined with the immunoglobulin (Ig) determinants present in the cytoplasm and surface membrane of lizard presumptive B lymphocytes. Immunofluorescence assays during the development of the T and B lineage showed that TA+ and Tt+ thymocytes increased from 35% at stage 37 to 96% at stage 41, and were exported precociously to the embryonic splenic environment. Embryonic thymocytes were shown to totally lack surface Ig, whereas 40-50% of splenocytes carried cytoplasmic and/or surface membrane Ig determinants. The data revealed further the presence of a subset of splenocytes bearing the specific markers of both T and B cells.

Ontogeny of alloreactivity in the chicken thymus and spleen was studied in mixed lymphocyte cultures. Mixed lymphocyte reaction (MLR) to total major histocompatibility complex (MHC) (B-complex in chicken) disparity was first detected in the thymus of 16-day-old embryo and regularly detectable from the 18th embryonal day on. Small strain-specific differences in the strength and appearance of the response were, however, observed. MLR to class I MHC (B-F) antigen disparity was not detectable before hatching. Exogenous interleukin-2-containing supernatant added to the cultures had only a minor effect on MLR of embryonal thymocytes. In the spleen, MLR was first detectable in some strain combinations on day 3 and regularly found on the 7th day posthatching, indicating colonization of peripheral lymphoid organs by thymus-derived mature T cells. Our results show the association of phenotypic and functional maturation of chicken T cells. The ontogeny of alloreactivity can now be compared to the appearance of T cell receptor (TCR), CD4, and CD8-bearing cells in the thymus and peripheral lymphoid organs.