Novel mechanism for the impairment of cell proliferation in HIV-1 infection

Neurologic injury in isolated sulfite oxidase deficiency

BACKGROUND

We review clinical, neuroimaging, and genetic information on six individuals with isolated sulfite oxidase deficiency (ISOD).

METHODS

All patients were examined, and clinical records, biochemistry, neuroimaging, and sulfite oxidase gene (SUOX) sequencing were reviewed.

RESULTS

Data was available on six individuals from four nuclear families affected by ISOD. Each individual began to seize within the first week of life. neurologic development was arrested at brainstem reflexes, and severe microcephaly developed rapidly. neuroimaging within days of birth revealed hypoplasia of the cerebellum and corpus callosum and damage to the supratentorial brain looking like severe hypoxic-ischemic injury that evolved into cystic hemispheric white matter changes. Affected individuals all had elevated urinary S-sulfocysteine and normal urinary xanthine and hypoxanthine levels diagnostic of ISOD. Genetic studies confirmed SUOX mutations in four patients.

CONCLUSIONS

ISOD impairs systemic sulfite metabolism, and yet this genetic disease affects only the brain with damage that is commonly confused with the clinical and radiologic features of severe hypoxic-ischemic encephalopathy.

Lésions neurologiques dans le déficit isolé en sulfite oxydase.

Bioenergetics of T cell activation and death in HIV type 1 infection

Regressive morphological lesions, found in peripheral lymphocytes from HIV(+) patients, clearly conflict with normal cycle progression and with the execution of basic housekeeping and immune functions. With these lesions, circulating lymphocytes are destined to spontaneous and energy-independent cell lysis. By means of confocal microscopy and morphometry, we have quantified the rate of circulating T cells that are probably destined to emocatheresis in vivo. This rate includes lymphocytes in which nucleolin fragments have been scattered out of the nuclear region as a result of prelethal alterations in the nuclear membrane permeability. In terms of bioenergetics, these cells show evident anomalies in the energy production machinery that make them unable to carry out ATP-requiring functions. The extent of damaged cell fraction in peripheral blood reflects the frequency with which T lymphocytes leave lymphoid tissue to be cleared in hemocatheretic processes.

HIV-1 Viral Replication below 50 Copies/ml in Patients on Antiretroviral Therapy is not associated with CD8+ T-cell Activation

Objectives

To determine if the expression of CD38 on CD8+ T-cells could be used as a marker of viral replication <50 copies/ml in peripheral blood.

Methods

In a cross-sectional study of patients attending a single HIV clinic in London, an ultra-sensitive HIV RNA viral load assay, with a limit of detection of 3 copies/ml, was used to determine HIV-1 replication in plasma in 70 patients who had sustained viral suppression <50 copies/ml by bDNA assays. Immune activation using the expression of CD38 on CD8+ T-cells was also assessed in patients on antiretroviral therapy (ART) with sustained viral suppression, individuals with persistent low-level viraemia <400 copies/ml and subjects failing ART (viral load >400 copies/ml).

Results

There was no significant difference in the percentage of CD8+CD38++ T-cells between patients with <50 copies or <3 copies/ml. Immune activation was significantly increased in patients with persistent low-level viraemia and in subjects failing ART. CD4+ T-cell counts in patients on long-term successful ART are inversely associated with CD8+ T-cell activation.

Conclusions

T-cell activation in patients on long-term successful ART is not due to residual low-level viral replication in the blood compartment of HIV-1. CD8+ T-cell activation in this patient group appears to be associated with poor CD4+ T-cell recovery.

HIV-1 replication increases HIV-specific CD4+ T cell frequencies but limits proliferative capacity in chronically infected children

This study investigated the relationship between HIV-1 replication and virus (HIV-1; CMV)-specific CD4(+) T cell frequency and function in HIV-1-infected children. HIV-1 gag p55-specific CD4(+) T cell IFN-gamma responses were detected in the majority of children studied. p55-specific responses were detected less commonly and at lower frequencies in children with <50 copies/ml plasma HIV-1 RNA than in children with active HIV-1 replication. In children with <50 copies/ml plasma HIV-1, p55-specific responses were detected only in children with evidence of ongoing HIV-1 replication, indicating a direct relationship between HIV-1 replication and HIV-specific CD4(+) T cell frequencies. In contrast, p55-specific proliferative responses were detected more frequently in children with <50 copies/ml plasma HIV-1. CMV-specific CD4(+) responses were more commonly detected and at higher frequencies in CMV-coinfected children with suppressed HIV-1 replication. The lack of HIV-specific CD4(+) proliferative responses, along with the preservation of CMV-specific CD4(+) responses in children with controlled HIV-1 replication, suggests that viral replication may have deleterious effects on HIV-1 and other virus-specific CD4(+) responses. Vaccination to stimulate HIV-specific CD4(+) T cell responses in these children may synergize with antiretroviral therapy to improve the long-term control of viral replication, and may perhaps allow the eventual discontinuation of antiretroviral therapy.

Inhibition of thymidine synthesis by folate analogues induces a Fas-Fas ligand-independent deletion of superantigen-reactive peripheral T cells

Methotrexate (MTX), a folate antagonist with multiple enzymatic targets, is used in the treatment of malignancies as well as in autoimmune and chronic inflammatory diseases, and ZD1694 (tomudex), a water-soluble quinazoline specific inhibitor of thymidylate synthase (TS), is used in the treatment of adenocarcinomas. In this study, we investigated the effects of these folate analogues on superantigen (SAg)-reactive peripheral T cells in vivo. In BALB/c mice, staphylococcal enterotoxin B (SEB)-induced cytokine secretion, IL-2R (CD25) expression and early deletion of a fraction of SEB-reactive V(beta)8(+) T cells were not impaired by either MTX (7 mg/kg/day) or tomudex (5 mg/kg/day). However, both MTX and tomudex prevented V(beta)8-selective T cell expansion and accelerated their peripheral elimination. Administration of thymidine (500 mg/kg/12 h) completely abrogated this effect, indicating that inhibition of TS but not that of other folate-dependent enzymes was the main mechanism involved. Furthermore, a marked increase of apoptotic cells restricted to the V(beta)8(+) T cell subset indicated that proliferation inhibition was associated with apoptosis. In contrast with peripheral V(beta)8(+) T cell deletion, MTX and tomudex did not prevent the increase of V(beta)8(+) thymocytes triggered by SEB. Experiments in C57BL/6-lpr/lpr mice further demonstrated that deletion of V(beta)8(+) T cells induced by folate analogues was independent of Fas-Fas ligand interaction. Our results provide evidence that folate analogues may selectively delete dividing peripheral T cells through TS inhibition, but do not interfere with other events triggered by SAg.

The increased CD38 expressed by lymphocytes infected with HIV-1 is a fully active NADase

The NADase activity of the ectoenzyme CD38 on intact cells has been measured by a fluorometric assay using epsilon-NAD as a substrate. The enzyme activity was tested in the Daudi cell line, PHA-activated blasts and peripheral blood and tonsil lymphocytes from HIV-1-negative and -positive individuals. There was a direct correlation in all cells tested between the number of cell surface CD38 molecules added in the assay and the NADase activity of the same cells expressed as fluorescent units. This indicates that CD38 is expressed in its fully active form when up-regulated on T cells from HIV-1-infected patients. One of the suggested roles of the CD38 ectoenzyme is to degrade extra cellular NAD and thus recycle its permeable metabolites. This finding is consistent with the hypothesis that the increase in CD38 expression on lymphocytes during the chronic phase of HIV-1 infection is a mechanism to compensate for impaired capacity of these cells to synthesize ribonucleotides de novo.