Rationale for a vaccine using cellular-derived epitope presented by HIV isolates.

It has been clearly demonstrated that cellular antigens (HLA, beta 2-microglobulin) are incorporated at the virion surface. The same epitope derived from beta 2-microglobulin is presented on all virus isolates. The peptide was identified by blocking the neutralizing capacity of a monoclonal antibody directed to R7V epitope: using this peptide for developing an ELISA, we have detected antibodies in nonprogressor patients with neutralizing property to laboratory strains and primary isolates. Purified anti-R7V antibodies immunoprecipitate all HIV isolates at concentration dependent. R7V is immunogenic after rabbit immunization and induces HIV immunoprecipitating and neutralizing antibodies. The patient's as well as the immunized rabbit antibodies did not bind to any cell. No autoimmune disease is found in nonprogressor patients. For all these reasons, R7V is a good candidate for an universal AIDS vaccine.

A novel epitope R7V common to all HIV-1 isolates is recognized by neutralizing IgG found in HIV-infected patients and immunized rabbits.

We have previously reported that the presence of antibodies (Ab) directed to the beta2-microglobulin-derived peptide R7V in patient's serum correlated with the nonprogression to AIDS. In order to investigate whether R7V motif could represent a potential target for neutralization, we have immunopurified anti-R7V Ab from sera of nonprogressors, as well as from sera of rabbits injected with R7V. We showed that human as well as rabbit purified,anti-R7V IgG precipitated laboratory adapted strains, as well as primary isolates from different clades indicating that: (1) R7V epitope is a common motif presented at the surface of genetically divergent HIV-1 strains (2) R7V is immunogenic in vivo. When used in neutralizing assay, purified anti-R7V Ab from human or rabbit origin were shown to neutralize infection by HIV-1 laboratory adapted strains and HIV-1 primary isolates. All together, our results indicate that the R7V motif shared by all HIV strains could be considered as a possible candidate for an HIV vaccine.

Circulating cell adhesion molecules in HIV1-infected patients as indicator markers for AIDS progression.

Cell adhesion molecules play an important role during immune responses. Circulating (c) forms of these molecules have been used as monitors of disease progression. In this study, we have investigated serum levels of ICAM1, ICAM2, ICAM3 and VCAM1 in HIV-infected patients. Our results showed that levels of cICAMs and cVCAM1 are increased during HIV infection. Among an HIV-infected population, the cICAM2 level was higher in the asymptomatic group compared to the AIDS group. In contrast, the cICAM1 level was higher in the AIDS group compared to the asymptomatic group. No difference between the two groups was observed in cICAM3 and cVCAM1 levels. A significant correlation was found between cICAM1, cICAM2 and cVCAM1 in both populations. We also showed that the cICAM1/cICAM2 ratio was correlated with the increase in the c beta 2 microglobulin level and the decrease in CD4 T-cell counts in the AIDS group. These results indicate that serum cCAM1 and cICAM2 in HIV infection could be additional markers to discriminate between asymptomatic and progressor patients.

Regulation of lipopolysaccharide-induced tumor necrosis factor production by cyclosporin A in mice primed with muramyl dipeptide.

The effect of cyclosporin A (CsA) on tumor necrosis factor (TNF) or interleukin-6 (IL-6) production was evaluated in vivo in primed or unprimed mice challenged with lipopolysaccharide (LPS). Both pretreatment with BCG infection or with muramyl dipeptide (MDP) prior to LPS challenge resulted in an increase in the cytokine bioactivity level in the blood. CsA administration inhibited the TNF production. In unprimed mice, either normal or sensitized to LPS lethality by galactosamine treatment, a marked decrease in the cytokine level was observed after injection of CsA. After adrenalectomy, the yield of both TNF and IL-6 following LPS injection was markedly elevated but decreased by CsA administration. Ex vivo experiments have shown that the inhibitory effect of CsA could be demonstrated at the level of macrophages from mice previously given the drug. If mice had received MDP, in vitro responses of cells to LPS were enhanced but again CsA decreased the mRNA expression and protein secretion.

Differential role of interferon-gamma in the potentiating effect of muramyl peptides for enhanced responses to lipopolysaccharide in mice: effect of cyclosporin A.

Cyclosporin A (CsA) administration reduced mortality in mice sensitized to endotoxic toxicity by various agents, such as muramyl dipeptide (MDP) or a lipophilic derivative. CsA is an inhibitor of a variety of T cell responses, suggesting that muramyl peptides could influence LPS-induced effects via the release of lymphokine. The potentiation of TNF production by pretreatment with muramyl peptides was comparable in nude mice and in controls, indicating that it is a T-independent mechanism, and CsA produced a similar inhibition in both groups. Neutralizing antibody to IFN-gamma did not change the elevated TNF level obtained in the blood when LPS was given after a muramyl peptide. However, the same treatment with anti-IFN-gamma MAb prevented the death of mice challenged with LPS plus MDP or plus a lipophilic derivative displaying similar effects. In comparing three selected muramyl peptides, we also show that the priming effect could be dissociated from the toxic synergism with LPS.

Selective modulation of lipopolysaccharide-induced death and cytokine production by various muramyl peptides.

Pretreatment of animals with the adjuvant muramyl dipeptide enhances both the production of circulating tumor necrosis factor and the sensitivity to the lethal effect of a lipopolysaccharide (LPS) challenge. The present study examined the capacity of various adjuvant muramyl dipeptide derivatives to potentiate responsiveness to LPS administration. Cytokine levels in serum were determined at various time intervals after LPS administration by bioassays and immunoassays; the cytokines examined were tumor necrosis factor, interleukin-1, interleukin-6, and gamma interferon. The time course of cytokine response was not modified by the pretreatment, but most of the levels were strongly enhanced. However, of the four compounds which were found to be potent priming agents, only two caused an increased sensitivity to LPS lethality, showing that elevated titers of cytokines in serum were not correlated with host sensitization. Interestingly, previous studies have shown that these two compounds also display neurobiological properties, implying a possible role of the central nervous system in LPS lethality. However, two hydrophilic derivatives with low activity as priming agents were capable of decreasing the toxicity of LPS when given after the challenge in galactosamine-sensitized mice. These results illustrate the diversity of responses elicited by immunological priming. They raise unanswered questions on the importance of endogenous mediators in the pathophysiological alterations during toxic shock.

Modulation of lipopolysaccharide-induced cytokine gene expression in mouse bone marrow-derived macrophages by muramyl dipeptide.

Previous studies have shown that an i.v. injection of muramyl dipeptide (MDP) before a LPS challenge strongly potentiated serum TNF and IL-6 release in mice. Therefore the direct action of MDP was examined on TNF-producing cells, namely in macrophages stimulated or not by LPS. The level of TNF-alpha, IL-1 alpha, and IL-6 mRNA was determined in bone marrow-derived macrophages (BMM). A marked TNF-alpha mRNA accumulation was found between 1 and 6 h after stimulation with MDP or LPS. LPS-induced IL-1 alpha mRNA transcript was delayed (3 h) than those after MDP induction (1 h). Conversely, kinetic induction of the IL-6 mRNA transcript was delayed in MDP-treated BMM as compared with LPS-stimulated cells. MDP pretreatment of BMM for 3 h not only enhanced the total level of LPS-induced TNF-alpha, IL-1 alpha, and IL-6 mRNA (respectively 2.9-, 1.6-, and 2.4-fold increase), but it also delayed the kinetics of IL-1 alpha and IL-6 species accumulation. The enhancement induced by MDP pretreatment at the level of cytokine mRNA accumulation was correlated with an increase in LPS-induced TNF and IL-6 biologic activity production in supernatant fluids. In addition, in BMM from C3H/Hej mice MDP pretreatment enhanced the weak effect of LPS on TNF mRNA transcript accumulation and was required to produce LPS-induced TNF bioactivity. Our results suggest that MDP and LPS could act through distinct pathway(s) to induce cytokine gene expression. Moreover, the priming effect displayed by MDP could result in modulation of the LPS-induced cytokine gene expression at the transcriptional and/or post-transcriptional level.

Indirect and selective down-regulation of serum tumor necrosis factor-alpha release by interleukin-1 beta.

A selective inhibition of LPS-induced tumor necrosis factor-alpha (TNF) response in mice was caused by an injection of recombinant human interleukin-1 (IL-1). The decrease in serum TNF level reached 70 to 80 percent of the controls receiving LPS alone when IL-1 was given simultaneously or prior to the challenge. At the same time serum IL-6 release was more elevated. Ex vivo assays have shown that macrophages from IL-1 treated animals did not respond to LPS when stimulated immediately after harvesting but recovered their normal responsiveness after being cultured for 2 hours and then washed. In vitro with or without addition of IL-1, mouse elicited macrophages responded equally to LPS in releasing TNF. In the absence of a direct and lasting effect on TNF-producing cells, the host reaction responsible for the inhibitory effect of IL-1 could be related to the overproduction of corticosterone that occurred after IL-1 injection, since it was not observed in adrenalectomized animals. Indeed the blockade of corticoid secretion by indomethacin prevented the inhibition of TNF production induced by IL-1 administration before LPS challenge. TNF administration did not result in elevation of corticosterone level and in contrast to IL-1 enhanced the TNF response to LPS injection. In vitro and ex vivo assays have shown this enhanced response to LPS was linked to a direct and prolonged effect of TNF on TNF-producing cells. Muramyl dipeptide (MDP) which was used as a known priming agent for enhanced cytokine release had a similar effect on TNF-producing cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of endogenous glucocorticoid on endotoxin-induced production of circulating TNF-alpha.

Mice are quite resistant to LPS toxicity but even a small dose induced a monophasic production of circulating TNF. In BCG-treated mice challenged with LPS, the greater susceptibility was associated with the capacity of producing elevated levels of TNF in the blood. During pregnancy, after adrenalectomy, and particularly after treatment with galactosamine, smaller amounts of LPS were lethal in mice. Using adrenalectomized mice, which are less sensitive to LPS toxicity than galactosamine-treated mice, it was shown that smaller doses of LPS were effective in inducing TNF release in comparison with intact animals, and that larger concentrations of serum TNF were obtained. Pretreatment of adrenalectomized mice with MDP before LPS elicited a priming effect for an enhanced TNF production that reached levels comparable to that found in BCG-primed mice. Whatever was the yield of circulating TNF, the pattern of response was similar peaking at 1.5 to 2 h to LPS injection and returning to baseline values within 4 h. Prior administration of glucocorticoid was effective in preventing the release of serum TNF in adrenalectomized mice. The level and the kinetics of serum TNF following LPS injection were not modified in pregnant or in galactosamine-treated mice, and as in control animals glucocorticoid administration prior to LPS inhibited the TNF response.

Differential priming for endotoxin-induced circulating cytokine production by tumor necrosis factor-alpha and interleukin 1 beta.

In unprimed mice, a single injection of a non-lethal dose of lipopolysaccharide (LPS) produced a rise in tumor necrosis factor (TNF) and interleukin 6 (IL 6) activities. Peak serum concentrations were attained, respectively, 1.5 hr and 2.5 hr after the challenge. Pretreatment with recombinant human TNF-alpha (rHuTNF) had a priming effect for enhanced production of both serum cytokines without any change in kinetics. The enhancement was more pronounced in the TNF (15-fold) than in the IL 6 (4-fold) response. Recombinant murine TNF caused a comparable increase in LPS-induced cytokine release. In contrast, comparable pretreatment with another macrophage-derived cytokine, recombinant human interleukin 1 beta (HuIL1-beta), revealed a negative effect on LPS-induced TNF release whereas IL 6 in the blood reached levels similar to those found after priming with rTNF. Moreover, when administered in combination with rHuTNF, rHuIL1-beta inhibited the priming effect on TNF autocrine production.