[Pulmonary mucosa during the perinatal period: Can understanding of the lung help to combat the infant's sensitivity to bronchiolitis?] / La muqueuse pulmonaire en période périnatale : un monde à comprendre pour lutter contre la sensibilité du jeune à la bronchiolite.

Due to infection with the respiratory syncytial virus (RSV), bronchiolitis is the main respiratory disease in infants, and no effective treatments currently exist. The perinatal period is an important stage in the maturation of the lung mucosa, insofar as it largely determines the host's pulmonary reactivity to pathogens. Understanding the physiological, immunological and microbiological characteristics of the lungs in early life may lead to new innovative strategies against infectious agents. We hypothesize that the lung microbiota represents a regulatory factor of paramount importance in young people's health.

Efficacy of particle-based DNA delivery for vaccination of sheep against FMDV.

As an alternative strategy to classical inactivated viral vaccine against FMDV, naked DNA vaccine is attractive because of safety, flexibility and low cost. However DNA vaccination is usually poorly efficient in target species. Indeed we found that naked DNA plasmids encoding for P1-2A3C3D and GM-CSF proteins did not induce any detectable immunity against FMDV in sheep. Interestingly, we demonstrate herein that formulations of DNA on poly(D,L-lactide-co-glycolide) (PLG) or in lipofectin triggered divergent types of immune responses: PLG stimulated a T cell response and could elicit significant neutralising antibody titers, whereas lipofectin generated even higher antibody titers but no significant T cell response. The DNA/PLG regimen used in five sheep protected against clinical symptoms and viraemia and prevented the carrier state in four of them. Thus formulated DNA can be remarkably efficient against FMDV in a ruminant species that is usually refractory to DNA vaccination.

Type I IFN modulates the immune response induced by DNA vaccination to pseudorabies virus glycoprotein C.

DNA vaccines have the capacity to induce strong Th1-biased immune responses that are of major importance to providing protection against intracellular pathogens. In the present study we have focused on the role played by type I IFN in immune responses induced after DNA vaccination. Mice lacking the IFNAR1 chain of the type I IFN receptor (IFNAR K/O mice) were immunized with a plasmid encoding glycoprotein C of pseudorabies virus (PRV-gC). After DNA vaccination, wild-type (WT) mice showed features characteristic of Th1 immune responses, such as high IgG2a:IgG1 anti-PRV Ab ratio and antigen-specific IFN-gamma production by spleen cells. In contrast, IFNAR K/O mice showed a significantly lower IgG2a:IgG1 Ab ratio and IFN-gamma production. In addition, the percentage of CD8(+) and B lymph-node cells expressing CD69 after PRV-gC DNA vaccination was lower in IFNAR K/O than in WT mice. These results support a major role played by type I IFN in shaping Th1 immune responses after DNA vaccination. Codelivery of plasmids encoding IL-12 and IL-18 along with the plasmid encoding PRV-gC restored Th1 responses in IFNAR K/O mice.

Interferon-alpha-producing cells are localized in gut-associated lymphoid tissues in transmissible gastroenteritis virus (TGEV) infected piglets.

Transmissible gastroenteritis virus (TGEV) infection of piglets results in a very rapid and massive release of IFN-alpha in serum and secretions. The objective of this work was to characterize the IFN-alpha-producing cells (IPC) in tissues of TGEV-infected piglets. Caesarean-derived colostrum-deprived piglets were infected orally with the TGEV virulent Miller strain and IPC were characterized in situ by immunohistochemistry, using a rabbit anti-pig IFN-alpha antiserum. IPC were almost exclusively detected in intestinal tissues and mesenteric lymph nodes (MLN), as early as 6 h post inoculation (p.i.), with a peak at 12-18 h. They disappeared by 24 h. IPC were localized between enterocytes in the small intestine epithelial layer, in the lamina propria, around the Peyer's patches and, at highest frequency, in MLN. Very few IPC were present in the spleen and popliteal lymph nodes of infected piglets. Double immunohistochemical staining for IFN-alpha and leukocyte markers on MLN cryosections showed that IPC were mainly Swine Leukocyte Antigen (SLA) class II positive, and were not stained by an anti-macrophage (SWC3a) MAb. In addition, double staining with anti-TGEV and anti-IFN-alpha MAbs showed that viral antigens were present in MLN, close to IPC. These results show for the first time the presence of IPC in gut mucosa and gut-associated lymphoid tissues in response to an enteropathogenic virus. Moreover, this work shows that IFN-alpha released in serum is likely to originate almost exclusively from gut IPC triggered locally by viral antigens to produce IFN-alpha, since there were very few IPC in spleen or peripheral lymph nodes. MHC class II molecule expression by gut-associated IPC suggests that these cells may be the in vivo mucosal counterparts of the dendritic cells recently shown to produce IFN-alpha after in vitro viral induction.

Transient IFN-gamma synthesis in the lymph node draining a dermal site loaded with UV-irradiated herpes simplex virus type 1: an NK- and CD3-dependent process regulated by IL-12 but not by IFN-alpha/beta.

Our previous studies have shown that UV-inactivated, non-replicating herpes simplex virus type 1 (UV-HSV-1) triggers early and transient synthesis of IFN-alpha/beta in the mouse regional lymph node when delivered upstream (i.e. in the ear dermis). In this study, it is demonstrated, by use of a quantitative RT-PCR readout assay, that IFN-gamma mRNA expression was rapidly and transiently upregulated in draining lymph nodes when UV-HSV-1 was delivered in the ear dermis of C57Bl/6 mice. An increased number of IFN-gamma-producing cells was also detected in the lymph node by flow cytometric analysis. Two different subsets of cells, namely DX5(+) NK cells and CD3epsilon(+) T cells, accounted for this early IFN-gamma synthesis. Prompt upregulation of IFN-alpha and IL-12p40 mRNA was also recorded. We took advantage of IFN-alpha/beta-receptor knockout and wild-type 129 mice to study a potential role of IFN-alpha/beta in the signalling pathway leading to IFN-gamma transcription/translation. IFN-gamma mRNA upregulation still occurred in IFN-alpha/beta-receptor(-/-) mice, showing that IFN-alpha/beta was dispensable. The use of IL-12-neutralizing antibodies, prior to UV-HSV-1 delivery, confirmed the major role played by IL-12 in the early/transient IFN-gamma burst.

vig-1, a new fish gene induced by the rhabdovirus glycoprotein, has a virus-induced homologue in humans and shares conserved motifs with the MoaA family.

We used mRNA differential display methodology to analyze the shift of transcription profile induced by the fish rhabdovirus, viral hemorrhagic septicemia virus (VHSV), in rainbow trout leukocytes. We identified and characterized a new gene which is directly induced by VHSV. This VHSV-induced gene (vig-1) encodes a 348-amino-acid protein. vig-1 is highly expressed during the experimental disease in lymphoid organs of the infected fish. Intramuscular injection of a plasmid vector expressing the viral glycoprotein results in vig-1 expression, showing that the external virus protein is sufficient for the induction. vig-1 expression is also obtained by a rainbow trout interferon-like factor, indicating that vig-1 can be induced through different pathways. Moreover, vig-1 is homologous to a recently described human cytomegalovirus-induced gene. Accordingly, vig-1 activation may represent a new virus-induced activation pathway highly conserved in vertebrates. The deduced amino acid sequence of vig-1 is significantly related to sequences required for the biosynthesis of metal cofactors. This suggests that the function of vig-1 may be involved in the nonspecific virus-induced synthesis of enzymatic cofactors of the nitric oxide pathway.

Reconstituted coronavirus TGEV virosomes lose the virus ability to induce porcine interferon-alpha production.

The transmissible gastroenteritis virus (TGEV) is a coronavirus which induces a strong interferon-alpha (IFN-alpha) production in vivo and in vitro. Previous studies have shown that the TGEV external protein M plays a major role in IFN-alpha induction by a non-infectious virus, whereas protein S is not involved. The present study extended these results by showing that monoclonal antibodies (MAbs) directed at the external viral protein sM could not block IFN-alpha induction, which argues against a direct role for this protein. In the same type of blocking experiment, MAbs to the TGEV receptor aminopeptidase N did not inhibit IFN-alpha induction, which strongly indicates that viral replication or entry through the receptor is not needed for TGEV induction of IFN-alpha in leukocytes. In an attempt to isolate functional envelope proteins, TGEV virions were detergent-solubilized and reconstituted in virosomes. Although BIAcore antigenic analysis revealed that the three external viral proteins were present on the virosomes, these proteins were unable to induce IFN-alpha in porcine leukocytes, and seemed to compete with the native virus for IFN-alpha induction. These data indicated that IFN-alpha inducing interactions between TGEV external proteins and leukocytes required a complex native envelope protein structure which has been lost in the virosomes.

Reconstituted coronavirus TGEV virosomes lose the virus ability to induce porcine interferon-alpha production.

The transmissible gastroenteritis virus (TGEV) is a coronavirus which induces a strong interferon-alpha (IFN-alpha) production in vivo and in vitro. Previous studies have shown that the TGEV external protein M plays a major role in IFN-alpha induction by a non-infectious virus, whereas protein S is not involved. The present study extended these results by showing that monoclonal antibodies (MAbs) directed at the external viral protein sM could not block IFN-alpha induction, which argues against a direct role for this protein. In the same type of blocking experiment, MAbs to the TGEV receptor aminopeptidase N did not inhibit IFN-alpha induction, which strongly indicates that viral replication or entry through the receptor is not needed for TGEV induction of IFN-alpha in leukocytes. In an attempt to isolate functional envelope proteins, TGEV virions were detergent-solubilized and reconstituted in virosomes. Although BIAcore antigenic analysis revealed that the three external viral proteins were present on the virosomes, these proteins were unable to induce IFN-alpha in porcine leukocytes, and seemed to compete with the native virus for IFN-alpha induction. These data indicated that IFN-alpha inducing interactions between TGEV external proteins and leukocytes required a complex native envelope protein structure which has been lost in the virosomes.

In vivo induction of interferon-alpha in pig by non-infectious coronavirus: tissue localization and in situ phenotypic characterization of interferon-alpha-producing cells.

A low frequency peripheral blood mononuclear cell (PBMC) subpopulation, referred to as natural interferon-producing (NIP) cells, is described as producing interferon-alpha (IFN-alpha) following contact with non-infectious viral structures, namely viral glycoproteins. These cells are characterized in vitro as non-T, non-B, MHC class II+ and CD4+ cells. In this study, NIP cells were analysed in vivo after an intravenous injection of UV-inactivated transmissible gastroenteritis virus in newborn piglets, which resulted in strong serum IFN-alpha production. Splenocytes, but not PBMC, were the IFN-alpha producers in vivo. Using double immunohistochemical labelling for both IFN-alpha and leukocyte markers, we established that splenic NIP cells were not T or B cells. The majority were MHC class II+ and only a minority expressed a macrophage marker. NIP cells were localized in contact with MHC class II-expressing cells and T cells, which suggested that NIP cells might modulate the antiviral immune response.

Herpes simplex virus induces appearance of interferon-alpha/beta-producing cells and partially interferon-alpha/beta-dependent accumulation of leukocytes in murine regional lymph nodes.

As in vivo experimental system involving the local induction of interferon-alpha/beta (IFN-alpha/beta) responses was established in mice by injecting s.c. ultraviolet (UV)-inactivated herpes simplex virus (HSV) in the right ears, the left ears receiving phosphate-buffered saline (PBS) as a control. Circulating IFN-alpha/beta was present in blood as early as 6 h postinjection, and little or none was found 24 h postinjection. Identification of IFN-alpha/beta-producing cells, carried out by immunohistochemistry and in situ hybridization, demonstrated that the IFN response occurred mainly in the lymph node draining the HSV-injected ear and not in the contralateral lymph node. Occasionally, IFN-alpha/beta-producing cells were found in the spleen and in the skin. The injected HSV caused an inflammatory reaction in the skin and an almost threefold enlargement of the draining lymph node within 6 h. The latter was characterized by a general accumulation of all major lymphocyte subsets and a striking infiltration of neutrophils. Injection s.c. of neutralizing anti-IFN-alpha/beta antibodies before HSV injection reduced the increase in size of the draining lymph node by approximately 50% at 6 h, and no significant effects were seen at 24 h. The localization of cells producing IFN-alpha/beta in the lymph node and the capacity of such IFN-alpha/beta to at least partially mediate an early accumulation of cells suggest that the local IFN-alpha/beta response may have an important role in the initiation of early antiviral immune responses.