Biological weapons

Smallpox virus eradication was one of the greatest successes of the 20th century. Moreover, the quest to combat its use in biological warfare, has fueled efforts to understand residual immune memory and to develop new animal models by the scientific community. Although the literature is full of animal studies of vaccinia virus infection, continuing efforts have helped to increase our knowledge regarding humoral and cellular memory to non-persistent pathogens and to study factors that might influence further vaccination strategies in humans. In addition, the potent immunostimulatory action of poxvirus vectors has led to development and evaluation of new-generation vaccine candidates, which will be discussed in this review.

[Thymus function and autoimmunity]

PURPOSE

Thymus is the site of T-cell development and is essential for the induction of self-tolerance, by deletion of autoreactive T lymphocytes (negative selection) and by generation of regulatory T cells. Defect of the selection mechanism of both types of lymphocytes lead to autoimmune diseases.

CURRENT KNOWLEDGE AND KEY POINTS

Elimination of potentially self-reactive T cells in the thymus requires the intrathymic expression of ubiquitous and "tissue-specific" antigens. Some thymic antigen expressions are dependent on AIRE expression. Mutations in the AIRE gene that are associated with the absence of autoantigen expression in the thymus, defects in the peptide presentation or in apoptosis can allow autoreactive T cells to escape negative selection, and are associated with autoimmune diseases. Recent data are now available concerning the thymic selection of autoreactive regulatory T cells. The Foxp3 gene was recently shown to be predominantly expressed in regulatory T cells and could be a more specific marker of regulatory T cells than phenotypic markers.

FUTURE PROSPECTS AND PROJECTS

Animal models show that regulatory T cells injection or intrathymic inoculation of antigen lead to immunological tolerance in autoimmunity and transplantation. These novel strategies could be used in human.

Virological exploration of individuals with discordant HIV screening tests

Screening for HIV infection can use many algorithms. When two different HIV antibody assays are used, discordant results may occur. To discriminate between HIV seroconversion, HIV variant infection and false positive reactivity, 30 consecutive subjects with two discordant HIV antibody-screening assays were extensively investigated for HIV infection. No subject had HIV seroconversion or reached HIV seropositivity criteria after a follow-up of 3 months. By contrast 36% became HIV negative by the use of both HIV screening assays. p24 Antigen, HIV-1 RNA, HIV-1 DNA, HIV-2 DNA assays and HIV isolation by sensitive culture were unable to identify HIV infection in the 30 subjects with discordant HIV screening assays. The data suggest that the use of two HIV screening assays increase false-positive HIV results without increasing clinical sensitivity. To compliment follow-up of HIV screening, early testing for HIV RNA could be useful to identify or eliminate a recent infection.

Mutations of the 3' untranslated region of the SDF1 gene in apes and monkeys: potential impact on sensitivity to AIDS induced by lentiviruses

The comparison of the stromal cell-derived factor-1 (SDF1) gene 3' untranslated region (3'UTR) of four great ape and four monkey species with their human counterparts shows that the human SDF1-3'A mutation is present in primate species that are the most susceptible to lentivirus-induced AIDS and is absent in species that are particularly resistant to lentivirus-induced AIDS. The results enlighten the possible relationship between SDF1-3'UTR polymorphism and sensitivity to AIDS.

Chlamydia pneumoniae induces interleukin-10 production that down-regulates major histocompatibility complex class I expression

Recently, it was demonstrated that CD8(+) T cells are important for the response against Chlamydia pneumoniae. By use of the human monocytic cell line U937 and human monocytes taken from peripheral blood, we investigated the effect of infection on various molecules critical for CD8(+) T cell function. A strong secretion of interleukin (IL)-10 by infected cells was observed, together with an inhibited expression of major histocompatibility complex (MHC) class I antigens, but without significant alteration of tumor growth factor-beta secretion or MHC class II expression. Recombinant IL-10 added to uninfected U937 cells decreased the expression of MHC class I, whereas blocking antibodies to IL-10 and its receptor abolished the C. pneumoniae-induced inhibition of MHC class I expression. Analysis of our data provides evidence that IL-10 secretion induced by C. pneumoniae infection of monocytic cells down-regulates the expression of MHC class I molecules and thereby might reduce the presentation of bacterial epitopes by MHC. This would decrease the ability of CD8(+) T cells to eliminate infected cells.

Shift in HIV resistance genotype after treatment interruption and short-term antiviral effect following a new salvage regimen

OBJECTIVE

To investigate the changes in genotypic drug-resistance pattern, plasma HIV RNA and CD4 cell count after treatment interruption and assess the short-term antiviral effect of a new salvage regimen.

DESIGN

Prospective study of 38 patients with multiple failing regimens who had completely stopped all medication for 3 months before a three to five-drug regimen was reintroduced according to clinical guidelines.

METHODS

Patients were tested for HIV resistance before and after treatment interruption by population-based sequencing and clonal analysis of selected patients.

RESULTS

Discontinuation of therapy for 3 months was associated with a median increase in HIV RNA of 0.4 log10 and a median decrease in CD4 cell count of 43 x 10(6)/l. Sixty-one per cent of patients had a shift from the drug-resistant genotype to a predominantly wild-type genotype. The patients significantly likely to show genotype reversion were those in Centers for Disease Control groups A or B, who had been exposed to few drugs, had a low plasma HIV RNA, or a high CD4 cell count. The only independent factor predicting genotype reversion was the clinical stage. The median change in plasma HIV RNA at month 3 after treatment reintroduction was -2.3 log10 copies/ml in patients who had genotype reversion compared with -0.6 log10 copies/ml in patients without genotype reversion (P = 0.004).

CONCLUSION

Suspending treatment for 3 months after multiple failures could be a suitable strategy for optimizing salvage therapy provided it is instituted early, before the HIV disease becomes too advanced.

[Neonatal type 1 pneumococcal meningitis and maternal septicemia]

The most common organisms in neonatal meningitis are group B streptococcus and Gram negative enteric bacteriae. Although Neisseria meningitidis, Haemophilus influenzae and Streptococcus pneumoniae are the most frequent causes of meningitis in infancy and childhood, they are uncommon in newborns. We report one case of neonatal meningitis and maternal septicemia.