CD38 stimulation lowers the activation threshold and enhances the alloreactivity of cord blood T cells by activating the phosphatidylinositol 3-kinase pathway and inducing CD73 expression

We have recently described in cord blood T cells (CBTC) a novel pathway linking CD38 and CD73, two signal transducers with ecto-enzyme activity. The aim of this study was 2-fold: first, to characterize the mechanisms by which CD38 regulates CD73 expression; and second, to determine whether surface-induced CD73 modulates CBTC responses. A marked increase in CD73 expression was observed in CD38+ cells after incubation with the appropriate CD38 mAbs. The induction of CD73 was blocked by wortmannin, a specific inhibitor of phosphatidylinositol 3-kinase (PI3-K). CD38 stimulation induced tyrosine phosphorylation of the p85 regulatory subunit of PI3-K and its association with other tyrosine-phosphorylated proteins. Surface-induced CD73 was as efficient in delivering activatory signals as the CD73 constitutively expressed on adult T cells. Highly CBTC, totally unresponsive to mitogenic concentrations of plastic-immobilized CD3 mAb, proliferated vigorously when exposed to the combination of plastic-immobilized CD3 and CD73 mAbs. The reactivity to allogeneic irradiated PBMC was also significantly enhanced by CD38 stimulation and was dependent on CD73 expression. Thus, CD38 stimulation lowers the activation threshold of CBTC by the CD3/TCR complex and enhances their reactivity to allogeneic cells via activation of the PI3-kinase pathway and CD73 expression.     

The changing face of AIDS-related opportunism: cryptococcosis in the highly active antiretroviral therapy (HAART) era. Case reports and literature review

Only nine cases of AIDS-related cryptococcosis have been reported until now in patients receiving highly active antiretroviral therapy (HAART), all of them with abnormal clinical features. Two HIV-infected patients who experienced an atypical relapse of cryptococcosis shortly after the start of HAART and despite maintenance antifungal treatment, are described. Six different relapses of cryptococcal meningitis were observed in a 28-month period in a patient who obtained a poor immune recovery after HAART (as shown by a CD4+ lymphocyte count ranging from 78 to 149 cells/microL, opposed to a baseline level of 98 cells/microL). On the other hand, a patient with favorable immunological response to HAART (as expressed by a CD4+ count growing from 7 to 186 cells/microL), experienced isolated multiple indolent cryptococcal abscesses involving head, neck, the anterior thoracic wall, and regional lymph nodes, with repeatedly negative cultures, and diagnosis obtained by both histopathologic study and positive serum antigen assay. Both our case reports are representative of novel correlations between opportunistic pathogens and immune reactivity, descending from the introduction of HAART. The first episode describes an exceedingly elevated number of disease relapses despite HAART and antifungal maintenance treatment, which may descend from an incomplete immune response to antiretroviral therapy, possibly responsible for failure in obtaining eradication of yeasts, but also for lack of disease dissemination (usually leading to a lethal multivisceral involvement in the pre-HAART era). The abnormal disease course and localization of second reported patient well depicts an "immune reconstitution syndrome" probably representing a flare-up of a latent fungal infection, caused by a rapidly effective HAART. In patients treated with HAART, AIDS-related cryptococcosis cannot therefore be ruled out by the absence of neurological involvement, and by persistingly negative cultures.     

Human monoclonal antibodies that inhibit binding of hepatitis C virus E2 protein to CD81 and recognize conserved conformational epitopes

The intrinsic variability of hepatitis C virus (HCV) envelope proteins E1 and E2 complicates the identification of protective antibodies. In an attempt to identify antibodies to E2 proteins from divergent HCV isolates, we produced HCV E2 recombinant proteins from individuals infected with HCV genotypes 1a, 1b, 2a, and 2b. These proteins were then used to characterize 10 human monoclonal antibodies (HMAbs) produced from peripheral B cells isolated from an individual infected with HCV genotype 1b. Nine of the antibodies recognize conformational epitopes within HCV E2. Six HMAbs identify epitopes shared among HCV genotypes 1a, 1b, 2a, and 2b. Six, including five broadly reactive HMAbs, could inhibit binding of HCV E2 of genotypes 1a, 1b, 2a, and 2b to human CD81 when E2 and the antibody were simultaneously exposed to CD81. Surprisingly, all of the antibodies that inhibited the binding of E2 to CD81 retained the ability to recognize preformed CD81-E2 complexes generated with some of the same recombinant E2 proteins. Two antibodies that did not recognize preformed complexes of HCV 1a E2 and CD81 also inhibited binding of HCV 1a virions to CD81. Thus, HCV-infected individuals can produce antibodies that recognize conserved conformational epitopes and inhibit the binding of HCV to CD81. The inhibition is mediated via antibody binding to epitopes outside of the CD81 binding site in E2, possibly by preventing conformational changes in E2 that are required for CD81 binding.     

Effect of ligand binding on human d-amino acid oxidase: Implications for the development of new drugs for schizophrenia treatment

In human brain the flavoprotein D ‐amino acid oxidase (hDAAO) is responsible for the degradation of the neuromodulator D ‐serine, an important effector of NMDA‐receptor mediated neurotransmission. Experimental evidence supports the concept that D ‐serine concentration increase by hDAAO inhibition may represent a valuable therapeutic approach to improve the symptoms in schizophrenia patients. This study investigated the effects on hDAAO conformation and stability of the substrate D ‐serine (or of the pseudo‐substrate trifluoro‐D ‐alanine), the FAD cofactor, and two inhibitors (benzoate, a classical substrate‐competitive inhibitor and the drug chlorpromazine (CPZ), which competes with the cofactor). We demonstrated that all these compounds do not alter the interaction of hDAAO with its physiological partner pLG72. The ligands used affect the tertiary structure of hDAAO differently: benzoate or trifluoro‐D ‐alanine binding increases the amount of the holoenzyme form in solution and stabilizes the flavoprotein, while CPZ binding favors a protein conformation resembling that of the apoprotein, which is more sensitive to degradation. Interestingly, the apoprotein form of hDAAO binds the substrate D ‐serine: this interaction increases FAD binding thus increasing the amount of active holoenzyme in solution. Benzoate and CPZ similarly modify the short‐term cellular D ‐serine concentration but affect the cellular concentration of hDAAO differently. In conclusion, the different alteration of hDAAO conformation and stability by the ligands used represents a further parameter to take into consideration during the development of new drugs to cope schizophrenia.     

The changing face of AIDS-related opportunism: Cryptococcosis in the highly active antiretroviral therapy (HAART) era. Case reports and literature review

Only nine cases of AIDS-related cryptococcosis have been reported until now in patients receiving highly active antiretroviral therapy (HAART),all of them with abnormal clinical features. Two HIV-infected patients who experienced an atypical relapse of cryptococcosis shortly after the start of HAART and despite maintenance antifungal treatment, are described. Six different relapses of cryptococcal meningitis were observed in a 28-month period in a patient who obtained a poor immune recovery after HAART (as shown by a CD⁴⁺ lymphocyte count ranging from 78 to 149 cellsL, opposed to a baseline level of 98 cellsL). On the other hand, a patient with favorable immunological response to HAART(as expressed by a CD⁴⁺ count growing from 7 to 186 cellsL),experienced isolated multiple indolent cryptococcal abscesses involving head,neck, the anterior thoracic wall, and regional lymph nodes, with repeatedly negative cultures, and diagnosis obtained by both histopathologic study and positive serum antigen assay. Both our case reports are representative of novel correlations between opportunistic pathogens and immune reactivity, descending from the introduction of HAART. The first episode describes an exceedingly elevated number of disease relapses despite HAART and antifungal maintenance treatment, which may descend from an incomplete immune response to antiretroviral therapy, possibly responsible for failure in obtaining eradication of yeasts, but also for lack of disease dissemination (usually leading to a lethal multivisceral involvement in the pre-HAART era). The abnormal disease course and localization of second reported patient well depicts an immune reconstitution syndrome probably representing a flare-up of a latent fungal infection, caused by a rapidly effective HAART. In patients treated with HAART, AIDS-related cryptococcosis cannot therefore be ruled out by the absence of neurological involvement, and by persistingly negative cultures.This revised version was published online in October 2005 with corrections to the Cover Date.     

Differential expression of ecto-5' nucleotidase activity by functionally and phenotypically distinct subpopulations of human Leu-2+/T8+ lymphocytes

Subsets of Leu-2+/T8+ cytotoxic/suppressor T lymphocytes were isolated by using various methods of purification and were investigated for expression of ecto-5' nucleotidase (5'NT) enzyme activity by radiochemical, cytochemical, and ultrastructural techniques. By using both the radiochemical and the cytochemical methods. T4-OKM1- cells displayed higher 5'NT activity in comparison with the entire T4- subpopulation. Analyses of the subpopulations of T4- (and predominantly Leu-2+) cells defined by the Leu-15 or Lyt-1 (9.3) monoclonal antibodies demonstrated that T4-Leu-15- and T4-Lyt-1+ cells displayed high 5'NT activity, whereas virtually no activity was present in T4-Leu-15+ and T4-Lyt-1-cells. At the ultrastructural level, the 5'NT reaction product was detected on the plasma membrane of a proportion of nongranular Leu-2+/T8+ lymphocytes, but no activity was found on cells with a granular lymphocyte (GL) morphology. 5'NT activity was also analyzed in peripheral blood mononuclear cells from one patient with expanded numbers of GL and two patients with GL leukemia. The enzymatic activity was significantly lower in these patients than in normal controls. This study provides new cytochemical evidence demonstrating the heterogeneity of Leu-2+/T8+ cells, and indicates that the population with the suppressor phenotype and function (Leu-15+/Lyt-1-, GL morphology) displays low or absent 5'NT activity, whereas the population composed of cytotoxic cell precursors (Leu-15-/Lyt-1+, nongranular morphology) has high 5'NT activity. Implications of these data for the interpretation of low 5'NT activity described in several immunodeficiency states and lymphoproliferative disorders are discussed.