Sexual partners of patients infected with the hepatitis C virus (HCV) often have detectable HCV-specific T-cell responses in the absence of seroconversion, suggesting unapparent, spontaneously resolving infection. To determine whether differences in the evolutionary potential of bottlenecked inoculum may explain the low rate of HCV persistence after sexual exposure, we have investigated changes in the entire HCV nonstructural 3 (NS3) gene over time in a chronic carrier and compared his viral quasispecies with that of the acute-phase isolate of his sexual partner, who developed acute resolving hepatitis C. The overall rate of accumulation of mutations, estimated by regression analysis of six consecutive consensus NS3 sequences over 8 years, was 1.5 ؋ 10 ؊3 mutations per site per year, with small intersample fluctuations related to changes in environmental conditions. Comparison of quasispecies parameters in one isolate of the chronic carrier with those of the acute-phase isolate of the infected partner revealed a higher heterogeneity and lower proportion of nonsynonymous mutations in the former. All NS3 sequences from the acute-phase isolate clustered with a single sequence from the chronic isolate, despite complete HLA mismatch between the patients, suggesting bottlenecking during transmission. The low risk of viral persistence after sexual exposure to HCV may be related to the selection of a limited number of viral particles carrying a particular combination of mutations which may further limit the potential of a relatively homogeneous quasispecies to rapidly diversify and overcome the immune response of the exposed host.

Summary Tacrolimus is a widely used immunosuppressive agent. Although T cells are the main targets of these pharmacological drugs, antigen presentation may also be affected. Among antigen‐presenting cells, plasmacytoid dendritic cells (PDCs) are the main source of type I interferons upon microbial challenge, and are involved in several diseases and autoimmune disorders. The aim of this study was to evaluate whether tacrolimus can modulate the function of PDCs in vitro. Maturation and function of PDCs was determined using flow cytometry, enzyme‐linked immunosorbent assay and cytometry bead arrays. The effect of tacrolimus on PDCs was observed mainly when the cells were pretreated with the immunosuppressive agent before activation. Upon dinucleotide–oligodeoxynucleotide (CpG–ODN) activation, tacrolimus pretreated PDCs showed a significant reduction in the surface expression of co‐stimulatory molecules and human leucocyte antigen D‐related (HLA‐DR) and secreted reduced levels of tumour necrosis factor (TNF)‐α. These results show that tacrolimus treatment of PDCs impairs CpG‐induced activation, which could affect the outcome of the immune response.

Objectives: To study the viral requirements for attachment, entry and infection using natural isolates of HCV (infectious plasma of a patient infected with HCV from genotype 1b) and a cell line which has previously been shown to support HCV replication (Daudi cells). Methods: We studied attachment of HCV to Daudi cells, a human B-cell line. Quantification was done by real-time RT-PCR. Results: The best attachment levels were obtained using plasma depleted of immunocomplexes. Results of kinetics of HCV attachment to Daudi cells show that attachment is maximum at pH 7.0, and that it decreased drastically at any other pH studied (5.5, 6.0, 6.5, 7.5 and 8.0). Conclusions: Depletion of immunocomplexes and pH control during infection are important parameters to improve attachment of HCV to Daudi cells using plasma as a natural source of virus.

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CD11b/CD18 (Mac-1) is a leukocyte integrin that plays a critical role in neutrophil adhesion and the initiation of acute inflammatory responses. Several Mac-1 blocking mAbs bind to the A-domain of CD11b, a approximately 200 amino acid region in the N-terminal portion of the protein that is involved in ligand binding and Mac-1 functional activity. We examined several CD11b blocking mAbs for different patterns of binding to A-domain. We used human/murine chimeric CD11b expression constructs and deletions of the A-domain to examine binding. We describe the binding characteristics of mAbs 60.1, LM2/1, LPM19C, M170, 44, and 904. All of these mAbs, except for 60.1, bind to the C-terminal half of the human A-domain (CD11b181-316). mAb 60.1 was unique in that it required regions of the N- and C-terminal ends of the A-domain for binding. mAbs 60.1, LPM19C, 904, and 44 all required the A-domain to be intact for binding. This suggests that these CD11b mAbs recognize a conformational epitope. LM2/1 was capable of binding to a fragment of the A-domain, CD11b285-300. Inasmuch as this system has been used to define different mAb binding sites, it may be used to analyze specific ligand binding sites in the A-domain of CD11b.