Pre-B-cell colony-enhancing factor,whose expression is up-regulated in activated lymphocytes,is a nicotinamide phosphoribosyltransferase,a cytosolic enzyme involved in NAD biosynthesis

The murine homologue of the previously identified human "pre-B-cell colony-enhancing factor" (PBEF) gene coding for a putative cytokine has been identified by screening a subtractive library enriched in genes expressed in activated T lymphocytes. Unlike most cytokine genes known to date, the PBEF gene is ubiquitously expressed in lymphoid and non-lymphoid tissues and displays significant homology with genes from primitive metazoans (marine sponges) and prokaryotic organisms. Recently, a bacterial protein encoded by nadV, a gene from the prokaryote Haemophilus ducreyi displaying significant homology with PBEF, has been identified as a nicotinamide phosphoribosyltranferase (NAmPRTase), an enzyme involved in nicotinamide adenine dinucleotide (NAD) biosynthesis. Using a panel of antibodies to murine PBEF, we demonstrate in this work that, similarly to its microbial counterpart, the murine protein is a NAmPRTase, catalyzing the condensation of nicotinamide with 5-phosphoribosyl-1-pyrophosphate to yield nicotinamide mononucleotide, an intermediate in the biosynthesis of NAD. The role of PBEF as a NAmPRTase was further confirmed by showing that the mouse gene was able to confer the ability to grow in the absence of NAD to a NAmPRTase-defective bacterial strain. The present findings are in keeping with the ubiquitous nature of this protein, and indicate that NAD biosynthesis may play an important role in lymphocyte activation.     

Murine Dendritic Cells Pulsed In Vitro with Toxoplasma gondii Antigens Induce Protective Immunity In Vivo

The activation of a predominant T-helper-cell subset plays a critical role in disease resolution. In the case of Toxoplasma gondii, the available evidence indicates that CD4⁺ protective cells belong to the Th1 subset. The aim of this study was to determine whether T. gondii antigens (in T. gondii sonicate [TSo]) presented by splenic dendritic cells (DC) were able to induce a specific immune response in vivo and to protect CBA/J mice orally challenged with T. gondii cysts. CBA/J mice immunized with TSo-pulsed DC exhibited significantly fewer cysts in their brains after oral infection with T. gondii 76K than control mice did. Protected mice developed a strong humoral response in vivo, with especially high levels of anti-TSo immunoglobulin G2a antibodies in serum. T. gondii antigens such as SAG1 (surface protein), SAG2 (surface protein), MIC1 (microneme protein), ROP2 through ROP4 (rhoptry proteins), and MIC2 (microneme protein) were recognized predominantly. Furthermore, DC loaded with TSo, which synthesized high levels of interleukin-12 (IL-12), triggered a strong cellular response in vivo, as assessed by the proliferation of lymph node cells in response to TSo restimulation in vitro. Cellular proliferation was associated with gamma interferon and IL-2 production. Taken together, these results indicate that immunization of CBA/J mice with TSo-pulsed DC can induce both humoral and Th1-like cellular immune responses and affords partial resistance against the establishment of chronic toxoplasmosis.     

Possible occurrence and meaning of lymphocytes bearing autoanti-idiotypic receptors during the immune response.

During an immune response, the increase in binding affinity of antibodies is followed by a fall. Lymphocytes bearing autoanti-idiotypic receptors were detected during a normal immune response. The kinetics of appearance and disappearance of such lymphocytes led us to propose a network model to explain the changes occurring in antibody properties during an immune response.     

Glucocorticoids down-regulate dendritic cell function in vitro and in vivo

Exogenous glucocorticoid hormones are widely used as therapeutical agents, whereas endogenous glucocorticoids may act as physiological immunosuppressants involved in the control of immune and inflammatory responses. The optimal activation of T lymphocytes requires two distinct signals: the major histocompatibility complex-restricted presentation of the antigen and an additional co-stimulatory signal provided by the antigen-presenting cells. There is ample evidence that, among the cells able to present the antigen, the dendritic cells (DC) have the unique property to activate antigen-specific, naive T cells in vitro and in vivo, and are therefore required for the induction of primary immune responses. In this work, we tested whether glucocorticoids affected the capacity of DC to sensitize naive T cells. Our data show that, in vitro, the steroid hormone analog dexamethasone (Dex) affects the viability of DC, selectively downregulates the expression of co-stimulatory molecules on viable DC, and strongly reduces their immunostimulatory properties. In vivo, a single injection of Dex results in impaired antigen presenting function, a finding which correlates with reduced numbers of splenic DC. These results show that glucocorticoids regulate DC maturation and immune function in vitro and in vivo and suggest that this mechanism may play a role in preventing overstimulation of the immune system.     

The adjuvant monophosphoryl lipid A increases the function of antigen-presenting cells

The induction of immune responses in vivo is typically performed with antigens administered in external adjuvants, like alum, complete Freund's adjuvant, LPS and, more recently, monophosphoryl lipid A (MPL). However, the role of the adjuvant is still poorly defined. The aim of this study was to test whether the MPL affects the function of antigen-presenting cells (APC) in vitro and in vivo. Antigen-pulsed APC [including macrophages, B cells and dendritic cells (DC)] were incubated or not with MPL, and their ability to sensitize naive T cells was tested in vitro and in vivo. The data show that MPL enhances the ability of macrophages and B cells to sensitize naive T cells, and confers to them the capacity to induce the development of T(h)1 and T(h)2. Administration of MPL i.v. in mice results in the redistribution of fully mature DC in the T cell area of the spleen. These observations suggest that MPL may induce an antigen-specific primary immune response by provoking the migration and maturation of DC that are the physiological adjuvant of the immune system.     

COMMON ORIGIN AND EVOLUTION OF VARIABLE AND CONSTANT REGIONS OF IMMUNOGLOBULINS

Sequence data show that the immunoglobulins evolved from two sets of paralogous genes: a gene set coding for the V regions and another for the different C regions. A comparison of sequences from these two gene sets shows homology between the V and C sets of genes: this homology is only significant when V_H is compared with Cμ1, Cμ2 and Cγ1. There is a close agreement between our data drawn from sequence comparisons and the data of Poljak et al. (1974) drawn from crystallographic data. This finding is in agreement with the results of the phylogenetic trees of the C and V gene sets: they suggest that the V_H subgroups and the first constant domain of the heavy chains are the most ancient. Moreover homology between the red blood cell glycophorin and Cμ2 suggests that immunoglobulins could have a common origin with some membrane proteins.     

Immunohistowax processing, a new fixation and embedding method for light microscopy, which preserves antigen immunoreactivity and morphological structures: visualisation of dendritic cells in peripheral organs

AIMS: To describe a new fixation and embedding method for tissue samples, immunohistowax processing, which preserves both morphology and antigen immunoreactivity, and to use this technique to investigate the role of dendritic cells in the immune response in peripheral tissues. METHODS: This technique was used to stain a population of specialised antigen presenting cells (dendritic cells) that have the unique capacity to sensitise naive T cells, and therefore to induce primary immune responses. The numbers of dendritic cells in peripheral organs of mice either untreated or injected with live Escherichia coli were compared. RESULTS: Numbers of dendritic cells were greatly decreased in heart, kidney, and intestine after the inoculation of bacteria. The numbers of dendritic cells in the lung did not seem to be affected by the injection of E coli. However, staining of lung sections revealed that some monocyte like cells acquired morphological and phenotypic features of dendritic cells, and migrated into blood vessles. CONCLUSIONS: These observations suggest that the injection of bacteria induces the activation of dendritic cells in peripheral organs, where they play the role of sentinels, and/or their movement into lymphoid organs, where T cell priming is likely to occur.     

The heat stable antigen (CD24) is not required for the generation of CD4+ effector and memory T cells by dendritic cells in vivo

Previous work has established that CD24 is a costimulatory molecule for T-cell clonal expansion. Studies using CD24 -/- mice demonstrated that CD24 plays a critical role in the CD28-independent immune response against virus and soluble antigens. The role of CD24 on dendritic cells (DCs) has not been reported. Here, we compare the CD24(+/+) and CD24(-/-) DCs in the induction of initial clonal expansion and elicitation of memory CD4(+) T cells in vivo. Our results demonstrate that the CD24 expressed on DCs is essential neither for the induction of initial T-cell clonal expansion nor for elicitation of memory activity of primed T cells in vivo.     

Midgut malrotation,the reliability of sonographic diagnosis

We are unaware of any other anatomical study which deals with normal variations in the relationship between the superior mesenteric artery (SMA) and the superior mesenteric vein (SMV). In our investigation in the majority of cases, the SMV lies to the right of the SMA. It has been suggested that ultrasonographic demonstration of a left sided SMV, is characteristic of midgut malrotation so a prospective study was undertaken in order to try to correlate the position of the mesenteric vessels on Ultrasound with the radiological diagnosis of midgut malrotation on upper GI series. 427 children (95% infants) who were planned for upper GI investigation, have had color Doppler U.S. of the mesenteric vessels before the barium study. In 67 cases, the mesenteric vessels were obscured by intestinal gas. Among them, there were 2 cases of malrotation. Three different positions of the mesenteric vessels were found in the 360 remaining cases. 1) A left sided SMV was found in 4% of the cases, all had midgut malrotation on X-rays and at surgery. 2) A mesenteric vein anterior to the SMA was found in 5% of the cases, 28% had midgut malrotation. 3) A normal right sided SMV was found in 91% of the cases. However 3% of these had midgut malrotation. There are anatomical variations in the position of the mesenteric vessels and a normal relationship between SMA and SMV does not ecxclude the possibility of intestinal malrotation. Nevertheless, ultrasound remains a useful noninvasive screening technique for the diagnosis of midgut malrotation.Presented at the IPR meeting in Stockholm, May 1991. Selected for publication by an International Group of the ESPR