Nabil Bosco

A Consideration of Biomarkers to be Used for Evaluation of Inflammation in Human Nutritional Studies

To monitor inflammation in a meaningful way, the markers used must be valid: they must reflect the inflammatory process under study and they must be predictive of future health status. In 2009, the Nutrition and Immunity Task Force of the International Life Sciences Institute, European Branch, organized an expert group to attempt to identify robust and predictive markers, or patterns or clusters of markers, which can be used to assess inflammation in human nutrition studies in the general population. Inflammation is a normal process and there are a number of cells and mediators involved. These markers are involved in, or are produced as a result of, the inflammatory process irrespective of its trigger and its location and are common to all inflammatory situations. Currently, there is no consensus as to which markers of inflammation best represent low-grade inflammation or differentiate between acute and chronic inflammation or between the various phases of inflammatory responses. There are a number of modifying factors that affect the concentration of an inflammatory marker at a given time, including age, diet and body fatness, among others. Measuring the concentration of inflammatory markers in the bloodstream under basal conditions is probably less informative compared with data related to the concentration change in response to a challenge. A number of inflammatory challenges have been described. However, many of these challenges are poorly standardised. Patterns and clusters may be important as robust biomarkers of inflammation. Therefore, it is likely that a combination of multiple inflammatory markers and integrated readouts based upon kinetic analysis following defined challenges will be the most informative biomarker of inflammation.

Expansion of peripheral naturally occurring T regulatory cells by Fms-like tyrosine kinase 3 ligand treatment

Fms-like tyrosine kinase 3 ligand (FLT3L) plays a major role in dendritic cell (DC) biology. Deficiency of FLT3L causes a dramatic decrease in DC numbers, whereas increasing its availability (by repetitive injections for 7-10 days) leads to a 10-fold increase in DC numbers. In this study, we show that FLT3L treatment indirectly leads to an expansion of peripheral naturally occurring T regulatory cells (NTregs). The FLT3L-induced increase in NTregs was still observed in thymectomized mice, ruling out the role of the thymus in this mechanism. Instead, the increased number of NTregs was due to proliferation of preexisting NTregs, most likely due to favored interactions with increased number of DCs. In vitro, we show that DCs induce regulatory T-cell (Treg) proliferation by direct cell contact and in an interleukin-2-dependent, T-cell receptor-independent manner. FLT3L could prevent death induced by acute graft-versus-host disease (GVHD). This study demonstrates unique aspects in the regulation of Treg homeostasis by DCs, which were unappreciated until now. It also reinforces the relevance of FLT3L treatment in GVHD by its ability to increase both the number of tolerizing DCs and NTregs.

Cutting Edge: IL-7 Regulates the Peripheral Pool of Adult RORγ+ Lymphoid Tissue Inducer Cells

During fetal life, CD4+CD3− lymphoid tissue inducer (LTi) cells are required for lymph node and Peyer’s patch development in mice. In adult animals, CD4+CD3− cells are found in low numbers in lymphoid organs. Whether adult CD4+CD3− cells are LTi cells and are generated and maintained through cytokine signals has not been directly addressed. In this study we show that adult CD4+CD3− cells adoptively transferred into neonatal CXCR5−/− mice induced the formation of intestinal lymphoid tissues, demonstrating for the first time their bona fide LTi function. Increasing IL-7 availability in wild-type mice either by IL-7 transgene expression or treatment with IL-7/anti-IL-7 complexes increased adult LTi cell numbers through de novo generation from bone marrow cells and increased the survival and proliferation of LTi cells. Our observations demonstrate that adult CD4+lineage− cells are LTi cells and that the availability of IL-7 determines the size of the adult LTi cell pool.

Crucial Role for BAFF-BAFF-R Signaling in the Survival and Maintenance of Mature B Cells

Defects in the expression of either BAFF (B cell activating factor) or BAFF-R impairs B cell development beyond the immature, transitional type-1 stage and thus, prevents the formation of follicular and marginal zone B cells, whereas B-1 B cells remain unaffected. The expression of BAFF-R on all mature B cells might suggest a role for BAFF-R signaling also for their in vivo maintenance. Here, we show that, 14 days following a single injection of an anti-BAFF-R mAb that prevents BAFF binding, both follicular and marginal zone B cell numbers are drastically reduced, whereas B-1 cells are not affected. Injection of control, isotype-matched but non-blocking anti-BAFF-R mAbs does not result in B cell depletion. We also show that this depletion is neither due to antibody-dependent cellular cytotoxicity nor to complement-mediated lysis. Moreover, prevention of BAFF binding leads to a decrease in the size of the B cell follicles, an impairment of a T cell dependent humoral immune response and a reduction in the formation of memory B cells. Collectively, these results establish a central role for BAFF-BAFF-R signaling in the in vivo survival and maintenance of both follicular and marginal zone B cell pools.

Peripheral T Cell Lymphopenia and Concomitant Enrichment in Naturally Arising Regulatory T Cells: The Case of the Pre-Tα Gene-Deleted Mouse

In pre-Tα (pTα) gene-deleted mice, the positively selectable CD4+CD8+ double-positive thymocyte pool is only 1% that in wild-type mice. Consequently, their peripheral T cell compartment is severely lymphopenic with a concomitant increase in proportion of CD25+FoxP3+ regulatory T cells. Using mixed bone marrow chimeras, where thymic output was 1% normal, the pTα−/− peripheral T cell phenotype could be reproduced with normal cells. In the pTα−/− thymus and peripheral lymphoid organs, FoxP3+CD4+ cells were enriched. Parabiosis experiments showed that many pTα−/−CD4+ single-positive thymocytes represented recirculating peripheral T cells. Therefore, the enrichment of FoxP3+CD4+ single-positive thymocytes was not solely due to increased thymic production. Thus, the pTα−/− mouse serves as a model system with which to study the consequences of chronic decreased thymic T cell production on the physiology of the peripheral T cell compartment.

Differential expression of regulator of G-protein signalling transcripts and in vivo migration of CD4+ naïve and regulatory T cells

The immune response of T lymphocytes to pathogens is initiated in draining secondary lymphoid organs, and activated cells then migrate to the site of infection. Thus, control of naïve and regulatory CD4+ T‐cell migration is crucial; however, it is poorly understood in physiological and pathological conditions. We found that CD4+ subpopulations displayed characteristic regulator of G‐protein signalling (RGS) gene expression profiles. Regulatory T cells express higher levels of RGS1, RGS9 and RGS16 than naïve cells. These genes are up‐regulated upon cell activation and their level of expression correlates with in vivo cell migration. Using parabiosis, we showed that regulatory T lymphocytes migrate less than naïve T cells and that migrant naïve T cells express even lower RGS levels than their static counterparts. Our results show an inverse correlation between the capacity to migrate and the levels of RGS1, RGS9 and RGS16 for both naïve and regulatory T cells. Taken together, these results suggest a role for RGS molecules in chemokine‐induced lymphocyte migration and demonstrate the peculiarity of regulatory T cells in terms of phenotype and migration ability, providing new insights into their function.

Tolerance checkpoints in B-cell development: Johnny B good

B‐cell development up to the immature B‐cell stage takes place in the bone marrow, while final maturation into mature B cells occurs in the spleen. During differentiation, the precursor and immature B cells have to pass several checkpoints, including those in which they are censored for being auto‐reactive, and therefore being potentially dangerous. Numerous studies have shown that the immature B‐cell stage in the bone marrow and the transitional B‐cell stages in the spleen comprise distinct checkpoints at which auto‐reactivity is censored. Recently, evidence has been provided that the large pre‐BII stage in the bone marrow, at which the pre‐BCR is expressed, is yet another B‐cell tolerance checkpoint. Here, we review these findings and speculate on directions for possible further experimentation.

Effects of Increasing IL-7 Availability on Lymphocytes during and after Lymphopenia-Induced Proliferation

IL-7 is critically involved in regulating peripheral T cell homeostasis. To investigate the role of IL-7 on lymphopenia-induced proliferation of polyclonal lymphocytes, we have transferred CFSE-labeled cells into a novel T-lymphopenic, IL-7-transgenic mouse line. Results obtained indicate that T and B cells do not respond in the same way to IL-7-homeostatic signals. Overexpression of IL-7 enhances proliferation of both CD4+ and CD8+ T cells but with distinctly temporal effects. Expansion of naturally arising CD4+-regulatory T cells was like that of conventional CD4+ T cells. IL-7 had no effect on B cell proliferation. By immunohistology, transferred T cells homed to T cell areas of spleen lymphoid follicles. Increasing IL-7 availability enhanced T cell recovery by promoting cell proliferation and reducing apoptosis during early stages of lymphopenia-induced proliferation. Taken together, these results provide new insights into the pleiotropic effects of IL-7 on lymphopenia-induced T cell proliferation.

Time-resolved Quantitative Proteome Analysis of In Vivo Intestinal Development

Postnatal intestinal development is a very dynamic process characterized by substantial morphological changes that coincide with functional adaption to the nutritional change from a diet rich in fat (milk) to a diet rich in carbohydrates on from weaning. Time-resolved studies of intestinal development have so far been limited to investigation at the transcription level or to single or few proteins at a time. In the present study, we elucidate proteomic changes of primary intestinal epithelial cells from jejunum during early suckling (1–7 days of age), middle suckling (7–14 days), and weaning period (14–35 days) in mice, using a label-free proteomics approach. We show differential expression of 520 proteins during intestinal development and a pronounced change of the proteome during the middle suckling period and weaning. Proteins involved in several metabolic processes were found differentially expressed along the development. The temporal expression profiles of enzymes of the glycolysis were found to correlate with the increase in carbohydrate uptake at weaning, whereas the abundance changes of proteins involved in fatty acid metabolism as well as lactose metabolism indicated a nondiet driven preparation for the nutritional change at weaning. Further, we report the developmental abundance changes of proteins playing a vital role in the neonatal acquisition of passive immunity. In addition, different isoforms of several proteins were quantified, which may contribute to a better understanding of the roles of the specific isoforms in the small intestine. In summary, we provide a first, time-resolved proteome profile of intestinal epithelial cells along postnatal intestinal development.

Peripheral T Lymphocytes Recirculating Back into the Thymus Can Mediate Thymocyte Positive Selection

The thymus continuously produces T lymphocytes that contribute to the maintenance of the peripheral T cell pool. Since peripheral recirculating T cells represent a very minor population among total thymocytes in normal animals, the relationship between the thymus and secondary lymphoid organs is generally considered unidirectional. Recently, several reports have described the presence of recirculating T cells in the thymus, raising issues regarding their possible function. In this article, we show that the niche for recirculating T cells in the thymus, i.e., their absolute number, is the same in lymphopenic and normal mice. Using a novel combination of TCR-transgenic mice in which the ligand necessary for positive selection of host T cells is only expressed by transferred donor T cells, we show that mature T cells recirculating back to the thymus can mediate positive selection.