Profiling Antibody Response Patterns in COVID-19: Spike S1-Reactive IgA Signature in the Evolution of SARS-CoV-2 Infection

This contribution explores in a new statistical perspective the antibody responses to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in 141 coronavirus disease 2019 (COVID-19) patients exhibiting a broad range of clinical manifestations. This cohort accurately reflects the characteristics of the first wave of the SARS-CoV-2 pandemic in Italy. We determined the IgM, IgA, and IgG levels towards SARS-CoV-2 S1, S2, and NP antigens, evaluating their neutralizing activity and relationship with clinical signatures. Moreover, we longitudinally followed 72 patients up to 9 months postsymptoms onset to study the persistence of the levels of antibodies. Our results showed that the majority of COVID-19 patients developed an early virus-specific antibody response. The magnitude and the neutralizing properties of the response were heterogeneous regardless of the severity of the disease. Antibody levels dropped over time, even though spike reactive IgG and IgA were still detectable up to 9 months. Early baseline antibody levels were key drivers of the subsequent antibody production and the long-lasting protection against SARS-CoV-2. Importantly, we identified anti-S1 IgA as a good surrogate marker to predict the clinical course of COVID-19. Characterizing the antibody response after SARS-CoV-2 infection is relevant for the early clinical management of patients as soon as they are diagnosed and for implementing the current vaccination strategies.

A fast and reliable method for detecting SNP rs67384697 (Hsa-miR-148a binding site) by a single run of allele-specific real-time PCR

Surface expression of human leukocyte antigen (HLA)-class I molecules is critical for modulating T/natural killer lymphocytes' effector functions. Among HLA molecules, HLA-C, the most recently evolved form of class I antigens, is subjected to both transcriptional and multiple post-transcriptional regulation mechanisms affecting its cell surface expression. Among the latter a region placed in the 3' untranslated region of HLA-C transcript contains the single nucleotide polymorphism (SNP) rs67384697 "G-ins/del" that has been found to be strictly associated with surface levels of HLA-C allomorphs because of the effect on the binding site of a microRNA (Hsa-miR-148a). Higher expression of HLA-C has been proved to influence HIV-1 infection via a better control of viremia and a slower disease progression. More importantly, the analysis of SNP rs67384697 "G-ins/del" combined with the evaluation of the HLA-Bw4/-Bw6 C1/C2 supratype, as well as the killer immunoglobulin-like receptor genetic asset, has proved to be pivotal in defining the status of Elite Controllers in the Caucasian population. Here we describe a new reliable and fast method of allele-specific real-time PCR to monitor the integrity/disruption of the binding site of the microRNA Hsa-miR-148a in a high-throughput format that can be easily applied to studies involving large cohorts of individuals.

Human Natural Killer Receptors, Co-Receptors, and Their Ligands

In the last 20 years, the study of human natural killer (NK) cells has moved from the first molecular characterizations of very few receptor molecules to the identification of a plethora of receptors displaying surprisingly divergent functions. We have contributed to the description of inhibitory receptors and their signaling pathways, important in fine regulation in many cell types, but unknown until their discovery in the NK cells. Inhibitory function is central to regulating NK-mediated cytolysis, with different molecular structures evolving during speciation to assure its persistence. More recently, it has become possible to characterize the NK triggering receptors mediating natural cytotoxicity, unveiling the existence of a network of cellular interactions between effectors of both natural and adaptive immunity. This unit reviews the contemporary history of molecular studies of receptors and ligands involved in NK cell function, characterizing the ligands of the triggering receptor and the mechanisms for finely regulating their expression in pathogen-infected or tumor cells. © 2018 by John Wiley & Sons, Inc.

Interdomain Stabilization Impairs CD4 Binding and Improves Immunogenicity of the HIV-1 Envelope Trimer

The HIV-1 envelope (Env) spike is a trimer of gp120/gp41 heterodimers that mediates viral entry. Binding to CD4 on the host cell membrane is the first essential step for infection but disrupts the native antigenic state of Env, posing a key obstacle to vaccine development. We locked the HIV-1 Env trimer in a pre-fusion configuration, resulting in impaired CD4 binding and enhanced binding to broadly neutralizing antibodies. This design was achieved via structure-guided introduction of neo-disulfide bonds bridging the gp120 inner and outer domains and was successfully applied to soluble trimers and native gp160 from different HIV-1 clades. Crystallization illustrated the structural basis for CD4-binding impairment. Immunization of rabbits with locked trimers from two different clades elicited neutralizing antibodies against tier-2 viruses with a repaired glycan shield regardless of treatment with a functional CD4 mimic. Thus, interdomain stabilization provides a widely applicable template for the design of Env-based HIV-1 vaccines.

Activating Killer Immunoglobulin Receptors and HLA-C: a successful combination providing HIV-1 control

Several studies demonstrated a relevant role of polymorphisms located within the HLA-B and -C loci and the Killer Immunoglobulin Receptors (KIRs) 3DL1 and 3DS1 in controlling HIV-1 replication. KIRs are regulatory receptors expressed at the surface of NK and CD8+ T-cells that specifically bind HLA-A and -B alleles belonging to the Bw4 supratype and all the -C alleles expressing the C1 or C2 supratype. We here disclose a novel signature associated with the Elite Controller but not with the long-term nonprogressor status concerning 2DS activating KIRs and HLA-C2 alleles insensitive to miRNA148a regulation. Overall, our findings support a crucial role of NK cells in the control of HIV-1 viremia.

HHV-8 DNA replication correlates with the clinical status in AIDS-related Kaposi's sarcoma

BACKGROUND

The value of plasma levels of human herpesvirus 8 (HHV-8) DNA as a marker of clinical status in acquired immunodeficiency syndrome-related Kaposi's sarcoma (AIDS-KS) remains to be elucidated.

OBJECTIVES

To investigate the relationship between the plasma HHV-8 DNA viral load and the clinical status of AIDS-KS.

STUDY DESIGN

A total of 378 blood samples were obtained from 62 patients with AIDS-KS followed longitudinally. All patients received antiretroviral therapy (ART) or anti-neoplastic therapy. The patients were divided into four groups according to their clinical status: onset disease (OD), progressive disease (PD), stable or partial remission (S/PR) and complete remission (CR).

RESULTS

Plasma HHV-8 DNAaemia was detected in all samples obtained from patients with OD or PD (100%); in contrast, HHV-8 DNAaemia was found only in a minority of patients with CR (8%) and was invariably undetectable in patients with stable CR. HHV-8 DNA detection in plasma was strongly associated with an unfavourable outcome (odds ratio=231.9; p<0.0001). Conversely, neither the HIV-1 viral load nor peripheral CD4(+) T-cell counts were associated with the KS clinical status, though both parameters did affect HHV-8 DNAaemia levels (p<0.0001). Multivariate analysis confirmed that HHV-8 DNAaemia was strongly and independently correlated with both clinical status (p<0.05) and HIV-1 plasma viraemia (p=0.027).

CONCLUSIONS

The strong association of plasma HHV-8 DNAaemia with onset or progressive disease is compatible with an active role of replicating virus in clinically active AIDS-KS. An accurate evaluation of the plasma HHV-8 load might be useful for monitoring AIDS-KS under antiretroviral or antineoplastic therapy.

Spontaneous control of HIV-1 viremia in a subject with protective HLA-B plus HLA-C alleles and HLA-C associated single nucleotide polymorphisms

Introduction

Understanding the mechanisms by which some individuals are able to naturally control HIV-1 infection is an important goal of AIDS research. We here describe the case of an HIV-1⁺ woman, CASE1, who has spontaneously controlled her viremia for the last 14 of her 20 years of infection.

Methods

CASE1 has been clinically monitored since 1993. Detailed immunological, virological and histological analyses were performed on samples obtained between 2009 and 2011.

Results

As for other Elite Controllers, CASE1 is characterized by low to undetectable levels of plasma HIV-1 RNA, peripheral blood mononuclear cell (PBMC) associated HIV-1 DNA and reduced in vitro susceptibility of target cells to HIV-1 infection. Furthermore, a slow rate of virus evolution was demonstrated in spite the lack of assumption of any antiretroviral agent. CASE1 failed to transmit HIV-1 to either her sexual male partner or to her child born by vaginal delivery. Normal values and ratios of T and B cells were observed, along with normal histology of the intestinal mucosa. Attempts to isolate HIV-1 from her PBMC and gut-derived cells were unsuccessful, despite expression of normal cell surface levels of CD4, CCRC5 and CXCR4. CASE1 did not produce detectable anti-HIV neutralizing antibodies in her serum or genital mucosal fluid although she displayed potent T cell responses against HIV-1 Gag and Nef. CASE1 also possessed multiple genetic polymorphisms, including HLA alleles (B*14, B*57, C*06 and C*08.02) and HLA-C single nucleotide polymorphisms (SNPs, rs9264942 C/C and rs67384697 del/del), that have been previously individually associated with spontaneous control of plasma viremia, maintenance of high CD4⁺ T cell counts and delayed disease progression.

Conclusions

CASE1 has controlled her HIV-1 viremia below the limit of detection in the absence of antiretroviral therapy for more than 14 years and has not shown any sign of immunologic deterioration or disease progression. Co-expression of multiple protective HLA alleles, HLA-C SNPs and strong T cell responses against HIV-1 proteins are the most likely explanation of this very benign case of spontaneous control of HIV-1 disease progression.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-014-0335-6) contains supplementary material, which is available to authorized users.

Calibrated real-time polymerase chain reaction for specific quantitation of HHV-6A and HHV-6B in clinical samples

The recent classification of human herpesvirus 6 (HHV-6) A and B, previously considered as two variants of the same virus, as two distinct herpesvirus species, emphasizes the need to develop and standardize specific methods for their detection and quantitation for clinical use. The development of two highly sensitive calibrated real-time PCR to quantify HHV-6A and -6B variants in clinical specimen is described. Both assays displayed the same wide linear dynamic range from 10(0) to 10(6) copies of viral DNA in a single reaction and sensitivity of one copy/reaction. These systems allow for HHV-6A/B DNA load quantitation in different types of clinical specimens: blood or tissue cells when combined with the CCR5 assay; cell-free samples (plasma or other biological fluids) in combination with the calibrator technology. Due to the absence of cross-amplification and cross-hybridization, these methods detect minute amounts of one viral species even in the presence of a large excess of the other, allowing a specific quantitation of both viruses in the case of mixed infections. The new qPCR methods provide sensitive and specific tool for monitoring HHV-6A/B DNA load in clinical samples, facilitating the study of these viruses in human diseases.

Comparison of oncogenic HPV type-specific viral DNA load and E6/E7 mRNA detection in cervical samples: results from a multicenter study

High-risk human papillomavirus (HR-HPV) genotype viral load and E6/E7 mRNA detection are proposed as surrogate markers of malignant cervical lesion progression. Currently, the use of commercially available DNA-based or mRNA-based tests is under investigation. In this study, the viral DNA load and E6/E7 mRNA detection of the five most common HR-HPV types detected in cervical cancer worldwide were compared in 308 cervical samples by using in-house type-specific quantitative real-time PCR assays and PreTect HPV-Proofer test, respectively. Sensitivity and negative predictive values were higher for the HPV-DNA assays combined (95.0% and 96.0%, respectively) than the RNA assays (77.0% and 88.0%, respectively); conversely, the mRNA test showed a higher specificity and higher positive predictive value (81.7% and 66.9%, respectively) than the DNA test (58.6% and 52.5%, respectively) for detecting histology-confirmed high-grade cervical intraepithelial neoplasia. A significantly higher association between viral DNA load and severity of disease was observed for HPV 16 and 31 (γ = 0.62 and γ = 0.40, respectively) than for the other HPV types screened. A good degree of association between the two assays was found for detection of HPV 16 (k = 0.83), HPV 18 (k = 0.72), HPV 33 (k = 0.66), and HPV 45 (k = 0.60) but not for HPV 31 (k = 0.24). Sequence analysis in L1 and E6-LCR regions of HPV 31 genotypes showed a high level of intra-type variation. HR-HPV viral DNA load was significantly higher in E6/E7 mRNA positive than negative samples (P < 0.001), except for HPV 31. These findings suggest that transcriptional and replicative activities can coexist within the same sample.

Treatment with IL-7 prevents the decline of circulating CD4+ T cells during the acute phase of SIV infection in rhesus macaques

Although treatment with interleukin-7 (IL-7) was shown to transiently expand the naïve and memory T-cell pools in patients with chronic HIV-1 infection receiving antiretroviral therapy (ART), it is uncertain whether a full immunologic reconstitution can be achieved. Moreover, the effects of IL-7 have never been evaluated during acute HIV-1 (or SIV) infection, a critical phase of the disease in which the most dramatic depletion of CD4⁺ T cells is believed to occur. In the present study, recombinant, fully glycosylated simian IL-7 (50 µg/kg, s.c., once weekly for 7 weeks) was administered to 6 rhesus macaques throughout the acute phase of infection with a pathogenic SIV strain (mac251); 6 animals were infected at the same time and served as untreated controls. Treatment with IL-7 did not cause clinically detectable side effects and, despite the absence of concomitant ART, did not induce significant increases in the levels of SIV replication except at the earliest time point tested (day 4 post-infection). Strikingly, animals treated with IL-7 were protected from the dramatic decline of circulating naïve and memory CD4⁺ T cells that occurred in untreated animals. Treatment with IL-7 induced only transient T-cell proliferation, but it was associated with sustained increase in the expression of the anti-apoptotic protein Bcl-2 on both CD4⁺ and CD8⁺ T cells, persistent expansion of all circulating CD8⁺ T-cell subsets, and development of earlier and stronger SIV Tat-specific T-cell responses. However, the beneficial effects of IL-7 were not sustained after treatment interruption. These data demonstrate that IL-7 administration is effective in protecting the CD4⁺ T-cell pool during the acute phase of SIV infection in macaques, providing a rationale for the clinical evaluation of this cytokine in patients with acute HIV-1 infection.

The development of highly effective cocktails of antiretroviral drugs has had a major impact on the survival and quality of life of individuals with HIV-1 infection. Yet, current protocols often fail to fully restore the immunologic function, a limitation that has prompted the clinical evaluation of immune-reconstitution agents, such as IL-7, as adjuvant therapies. To date, however, IL-7 has been tested exclusively in patients with chronic HIV-1 infection, while it appears that the immune system is irreparably damaged during acute primary infection, within the first few weeks after encountering the virus. We used a macaque model to show that treatment with IL-7 has beneficial effects if implemented during the acute phase of infection with SIV, the simian AIDS virus. Early administration of IL-7 was safe and effectively protected CD4⁺ T cells, the primary target cells for the virus, from the marked decline that typically occurs during acute SIV infection. Furthermore, IL-7 boosted the development of antiviral immune responses. Thus, IL-7 might be an effective adjuvant therapy in acute HIV-1 infection, which can protect the pool of CD4⁺ T cells before it is irreversibly compromised by the action of the virus.

A new antigen scanning strategy for monitoring HIV-1 specific T-cell immune responses

Delineation of the immune correlates of protection in natural infection or after vaccination is a mandatory step for vaccine development. Although the most recent techniques allow a sensitive and specific detection of the cellular immune response, a consensus on the best strategy to assess their magnitude and breadth is yet to be reached. Within the AIDS Vaccine Integrated Project (AVIP http://www.avip-eu.org) we developed an antigen scanning strategy combining the empirical-based approach of overlapping peptides with a vast array of database information. This new system, termed Variable Overlapping Peptide Scanning Design (VOPSD), was used for preparing two peptide sets encompassing the candidate HIV-1 vaccine antigens Tat and Nef. Validation of the VOPSD strategy was obtained by direct comparison with 15mer or 20mer peptide sets in a trial involving six laboratories of the AVIP consortium. Cross-reactive background responses were measured in 80 HIV seronegative donors (HIV-), while sensitivity and magnitude of Tat and Nef-specific T-cell responses were assessed on 90 HIV+ individuals. In HIV-, VOPSD peptides generated background responses comparable with those of the standard sets. In HIV-1+ individuals the VOPSD pools showed a higher sensitivity in detecting individual responses (Tat VOPSD vs. Tat 15mers or 20mers: p≤0.01) as well as in generating stronger responses (Nef VOPSD vs. Nef 20mers: p<0.001) than standard sets, enhancing both CD4 and CD8 T-cell responses. Moreover, this peptide design allowed a marked reduction of the peptides number, representing a powerful tool for investigating novel HIV-1 candidate vaccine antigens in cohorts of HIV-seronegative and seropositive individuals.

A multiplex calibrated real-time PCR assay for quantitation of DNA of EBV-1 and 2

Accurate and highly sensitive tests for the diagnosis of active Epstein-Barr virus (EBV) infection are essential for the clinical management of individuals infected with EBV. A calibrated quantitative real-time PCR assay for the measurement of EBV DNA of both EBV-1 and 2 subtypes was developed, combining the detection of the EBV DNA and a synthetic DNA calibrator in a multiplex PCR format. The assay displays a wide dynamic range and a high degree of accuracy even in the presence of 1μg of human genomic DNA. This assay measures with the same efficiency EBV DNA from strains prevalent in different geographic areas. The clinical sensitivity and specificity of the system were evaluated by testing 181 peripheral blood mononuclear cell (PBMCs) and plasma specimens obtained from 21 patients subjected to bone marrow transplantation, 70 HIV-seropositive subjects and 23 healthy controls. Patients affected by EBV-associated post-transplant lymphoprolipherative disorders had the highest frequency of EBV detection and the highest viral load. Persons infected with HIV had higher levels of EBV DNA load in PBMCs and a higher frequency of EBV plasma viremia compared to healthy controls. In conclusion, this new assay provides a reliable high-throughput method for the quantitation of EBV DNA in clinical samples.

Differentiated human neural stem cells: a new ex vivo model to study HHV-6 infection of the central nervous system

BACKGROUND

HHV-6 is the etiologic agent of exanthem subitum, a pediatric illness that may be associated with clinical and laboratory signs of central nervous system involvement. The absence of suitable experimental models has so far hampered the elucidation of the mechanisms of HHV-6-mediated neural cell damage. Recently, the growing knowledge in neurobiology has permitted the establishment of long-term cultures of human neural stem cells (hNSC) that, by virtue of their self-renewal capacity and multipotentiality, provide a valuable tool for the study of neurodegenerative disorders.

OBJECTIVES AND STUDY DESIGN

We studied the effects of HHV-6 infection in differentiated cultures of hNSC derived from the telencephalic and diencephalic regions of a 13.5 week post conception (pcw) fetal brain. The prototypic HHV-6 strain GS (subgroup A) was used.

RESULTS

hNSC were differentiated ex vivo to obtain mixed cultures encompassing astrocytes, neurons and oligodendrocytes. These differentiated hNSC cultures were found to be susceptible to productive HHV-6A infection, resulting in the formation of syncytia associated with phenotypic alterations.

CONCLUSION

These results demonstrate that hNSC may provide a physiologically relevant model to investigate the pathogenic role of HHV-6 in central nervous system disorders.

Human herpesvirus 6A accelerates AIDS progression in macaques

Although HIV is the necessary and sufficient causative agent of AIDS, genetic and environmental factors markedly influence the pace of disease progression. Clinical and experimental evidence suggests that human herpesvirus 6A (HHV-6A), a cytopathic T-lymphotropic DNA virus, fosters the progression to AIDS in synergy with HIV-1. In this study, we investigated the effect of coinfection with HHV-6A on the progression of simian immunodeficiency virus (SIV) disease in pig-tailed macaques (Macaca nemestrina). Inoculation of HHV-6A resulted in a rapid appearance of plasma viremia associated with transient clinical manifestations and followed by antibody seroconversion, indicating that this primate species is susceptible to HHV-6A infection. Whereas animals infected with HHV-6A alone did not show any long-term clinical and immunological sequelae, a progressive loss of CD4(+) T cells was observed in all of the macaques inoculated with SIV. However, progression to full-blown AIDS was dramatically accelerated by coinfection with HHV-6A. Rapid disease development in dually infected animals was heralded by an early depletion of both CD4(+) and CD8(+) T cells. These results provide in vivo evidence that HHV-6A may act as a promoting factor in AIDS progression.

Viral interactions in human lymphoid tissue: Human herpesvirus 7 suppresses the replication of CCR5-tropic human immunodeficiency virus type 1 via CD4 modulation

Human immunodeficiency virus (HIV) infection is often accompanied by infection with other pathogens that affect the clinical course of HIV disease. Here, we identified another virus, human herpesvirus 7 (HHV-7) that interferes with HIV type 1 (HIV-1) replication in human lymphoid tissue, where critical events of HIV disease occur. Like the closely related HHV-6, HHV-7 suppresses the replication of CCR5-tropic (R5) HIV-1 in coinfected blocks of human lymphoid tissue. Unlike HHV-6, which affects HIV-1 by upregulating RANTES, HHV-7 did not upregulate any CCR5-binding chemokine. Rather, the inhibition of R5 HIV-1 by HHV-7 was associated with a marked downregulation of CD4, the cellular receptor shared by HHV-7 and HIV-1. HHV-7-induced CD4 downregulation was sufficient for HIV-1 inhibition, since comparable downregulation of CD4 with cyclotriazadisulfonamide, a synthetic macrocycle that specifically modulates expression of CD4, resulted in the suppression of HIV infection similar to that seen in HHV-7-infected tissues. In contrast to R5 HIV-1, CXCR4-tropic (X4) HIV-1 was only minimally suppressed by HHV-7 coinfection. This selectivity in suppression of R5 and X4 HIV-1 is explained by a suppression of HHV-7 replication in X4- but not in R5-coinfected tissues. These results suggest that HIV-1 and HHV-7 may interfere in lymphoid tissue in vivo, thus potentially affecting the progression of HIV-1 disease. Knowledge of the mechanisms of interaction of HIV-1 with HHV-7, as well as with other pathogens that modulate HIV-1 replication, may provide new insights into HIV pathogenesis and lead to the development of new anti-HIV therapeutic strategies.

Productive infection of HUVEC by HHV-8 is associated with changes compatible with angiogenic transformations

Kaposi's Sarcoma (KS) is an angioproliferative disease associated with human herpesvirus 8 (HHV-8) infection. We have characterized the morphologic and phenotypic modifications of HUVEC in a model of productive HHV-8 infection. HHV-8 replication was associated with ultra-structural changes, flattened soma and a loss of marginal folds and intercellular contacts, and morphologic features, spindle cell conversion and cordon-like structures formation. Phenotypic changes observed on cordon-like structures included partial loss and redistribution of CD31/PECAM-1 and VE-cadherin, uPAR up-regulation and de novo expression of CD13/APN. Such changes demonstrate the induction, in HUVEC, of an angiogenic profile. Most of these findings are directly linked to HHV-8-encoded proteins expression, suggesting that HHV-8 itself may participate to the initial steps of the angiogenic transformation in KS.

Preparing for phase II/III HIV vaccine trials in Africa

Before performing phase II/III clinical trials in Africa, preliminary studies, including assessment and building up of clinical and laboratory infrastructures, estimates of human immunodeficiency virus incidence, investigation of the background immune response, and evaluation of the cross-clade immune response, need to be done. Plans and ongoing work in the context of the AIDS Vaccine Integrated Project and some preliminary data are presented.

Additional evidence that pityriasis rosea is associated with reactivation of human herpesvirus-6 and -7

To elucidate the role of human herpesvirus (HHV)-6 and -7 (HHV-7) in pityriasis rosea (PR), we measured their DNA load in plasma, peripheral blood mononuclear cells (PBMC), and tissues using a calibrated quantitative real-time PCR assay. We also studied HHV-6- and HHV-7-specific antigens in skin by immunohistochemistry and anti-HHV-7 neutralizing activity using a syncytia-inhibition test. Plasma and PBMC were obtained from 31 PR patients (14 children, 17 adults), 12 patients with other dermatites, and 36 blood donors. Skin biopsies were obtained from 15 adults with PR and 12 with other dermatites. HHV-6 and HHV-7 DNA were detected in 17% and in 39% of PR plasmas, respectively, but in no controls. HHV-7 viremia was associated with a higher PBMC load and, in adults, with systemic symptoms. HHV-7, but not HHV-6, levels in PBMC were higher in PR patients than in controls. HHV-6 and HHV-7 antigens were found only in PR skin (17% and 67% of patients analyzed, respectively), indicating a productive infection. Syncytia-neutralizing antibodies were found in PR patients and controls, but their titers were lower in patients with HHV-7 viremia. These data confirm the causal association between PR and active HHV-7 or, to a lesser extent, HHV-6 infection.

Additional evidence that pityriasis rosea is associated with reactivation of human herpesvirus-6 and -7

To elucidate the role of human herpesvirus (HHV)-6 and -7 (HHV-7) in pityriasis rosea (PR), we measured their DNA load in plasma, peripheral blood mononuclear cells (PBMC), and tissues using a calibrated quantitative real-time PCR assay. We also studied HHV-6- and HHV-7-specific antigens in skin by immunohistochemistry and anti-HHV-7 neutralizing activity using a syncytia-inhibition test. Plasma and PBMC were obtained from 31 PR patients (14 children, 17 adults), 12 patients with other dermatites, and 36 blood donors. Skin biopsies were obtained from 15 adults with PR and 12 with other dermatites. HHV-6 and HHV-7 DNA were detected in 17% and in 39% of PR plasmas, respectively, but in no controls. HHV-7 viremia was associated with a higher PBMC load and, in adults, with systemic symptoms. HHV-7, but not HHV-6, levels in PBMC were higher in PR patients than in controls. HHV-6 and HHV-7 antigens were found only in PR skin (17% and 67% of patients analyzed, respectively), indicating a productive infection. Syncytia-neutralizing antibodies were found in PR patients and controls, but their titers were lower in patients with HHV-7 viremia. These data confirm the causal association between PR and active HHV-7 or, to a lesser extent, HHV-6 infection.

A relapsing inflammatory syndrome and active human herpesvirus 8 infection

We describe an immunocompetent 61-year-old woman who was negative for human immunodeficiency virus and who had recurrent human herpesvirus 8 (HHV-8) infection associated with a relapsing systemic inflammatory syndrome characterized by fever, lymphadenopathy, splenomegaly, edema, arthrosynovitis, and rash. Kaposi's sarcoma developed 10 months after the initial clinical presentation. A correlation was documented between the recurrent clinical manifestations and the HHV-8 load in plasma and peripheral-blood mononuclear cells. Histologic examination of an enlarged lymph node heavily infected with HHV-8 revealed an atypical lymphoproliferative disorder characterized by paracortical hyperplasia and collapsed primary and secondary follicles.

Rapid diagnosis of mycobacterial infections and quantitation of Mycobacterium tuberculosis load by two real-time calibrated PCR assays

Sensitive and specific techniques to detect and identify Mycobacterium tuberculosis directly in clinical specimens are important for the diagnosis and management of patients with tuberculosis (TB). We developed two real-time PCR assays, based on the IS6110 multicopy element and on the senX3-regX3 intergenic region, which provide a rapid method for the diagnosis of mycobacterial infections. The sensitivity and specificity of both assays were established by using purified DNA from 71 clinical isolates and 121 clinical samples collected from 83 patients, 20 of whom were affected by TB. Both assays are accurate, sensitive, and specific, showing a complementary pattern of Mycobacterium recognition: broader for the IS6110-based assay and restricted to the M. tuberculosis complex for the senX3-regX3-based assay. Moreover, the addition of a synthetic DNA calibrator prior to DNA extraction allowed us to measure the efficiency of DNA recovery and to control for the presence of PCR inhibitors. The mycobacterial burden of the clinical samples, as assessed by direct microscopy, correlates with the M. tuberculosis DNA load measured by the senX3-regX3-based assay. In addition, reduced levels of M. tuberculosis DNA load are present in those patients subjected to successful therapy, suggesting a potential use of this assay for monitoring treatment efficacy. Therefore, these assays represent a fully controlled high-throughput system for the evaluation of mycobacterial burden in clinical specimens.

Human herpesvirus 8 (HHV-8/KSHV) and hematologic malignancies

Human herpesvirus 8 (HHV-8), also defined Kaposi's sarcoma (KS)-associated herpesvirus, was identified by Chang and colleagues in 1994 using purely molecular techniques, before any serological evidence or virus isolation in cell culture could be achieved. HHV-8 is unique among herpesviruses because its prevalence in the general population is low and because it possesses the richest weaponry of viral oncogenes and tumor-promoting factors ever described. Eleven HHV-8-specific genes are homologs of cellular genes, which were hijacked from the host during a long parallel evolution, and at least five of such genes show both in vitro and in vivo transforming ability. HHV-8 is the causative agent of KS, but it has also been associated with different hematologic malignancies, including primary effusion lymphoma (PEL), multicentric Castelman's disease (MCD), MCD-related immunoblastic/plasmablastic lymphoma and various atypical lymphoproliferative disorders. Although low-level silent infection was detected in bone marrow stromal cells from patients with multiple myeloma, a role of HHV-8 in this disease is unlikely. As seen with KS, the incidence of HHV-8-associated lymphoproliferative disorders is increased in the setting of human immunodeficiency virus infection.

Pathogenic effects of human herpesvirus 6 in human lymphoid tissue ex vivo

Human herpesvirus 6 (HHV-6) is a potentially immunosuppressive agent that has been suggested to act as a cofactor in the progression of human immunodeficiency virus disease. However, the lack of suitable experimental models has hampered the elucidation of the mechanisms of HHV-6-mediated immune suppression. Here, we used ex vivo lymphoid tissue to investigate the cellular tropism and pathogenic mechanisms of HHV-6. Viral strains belonging to both HHV-6 subgroups (A and B) were able to productively infect human tonsil tissue fragments in the absence of exogenous stimulation. The majority of viral antigen-expressing cells were CD4(+) T lymphocytes expressing a nonnaive phenotype, while CD8(+) T cells were efficiently infected only with HHV-6A. Accordingly, HHV-6A infection resulted in the depletion of both CD4(+) and CD8(+) T cells, whereas in HHV-6B-infected tissue CD4(+) T cells were predominantly depleted. The expression of different cellular antigens was dramatically altered in HHV-6-infected tissues: whereas CD4 was upregulated, both CD46, which serves as a cellular receptor for HHV-6, and CD3 were downmodulated. However, CD3 downmodulation was restricted to infected cells, while the loss of CD46 expression was generalized. Moreover, HHV-6 infection markedly enhanced the production of the CC chemokine RANTES, whereas other cytokines and chemokines were only marginally affected. These results provide the first evidence, in a physiologically relevant study model, that HHV-6 can severely affect the physiology of secondary lymphoid organs through direct infection of T lymphocytes and modulation of key membrane receptors and chemokines.

Calibrated real-time PCR assay for quantitation of human herpesvirus 8 DNA in biological fluids

Accurate laboratory tests for the diagnosis of active human herpesvirus 8 (HHV-8) infection are becoming essential to study the pathogenesis of HHV-8-associated tumors and for the clinical management of HHV-8-infected individuals. We have developed a highly sensitive, calibrated quantitative real-time PCR assay for the measurement of cell-free HHV-8 DNA in body fluids, based on the addition of a synthetic DNA calibrator prior to DNA extraction. The calibrator controls each sample for the presence of PCR inhibitors, determines a cutoff value of sensitivity for negative samples, and normalizes positive samples for the efficiency of DNA recovery. The assay shows a wide dynamic range of detection (between 1 and 10(6) viral genome equivalents/reaction) and a high degree of accuracy even in the presence of high amounts (up to 1 micro g) of human genomic DNA. Moreover, the assay has a very high sensitivity (lower detection limit, 10 genome equivalents/ml) and a high degree of reproducibility and repeatability with a coefficient of variation (CV) of <15 and 23%, respectively. Furthermore, the use of the calibrator improves the accuracy of quantitation and decreases the intersample variability (CV, 9 and 6%, respectively). The sensitivity and specificity of the assay were tested with a series of clinical specimens obtained from patients affected by various HHV-8-related diseases, as well as from a wide number of controls. In conclusion, our calibrated real-time PCR assay provides a reliable high-throughput method for quantitation of HHV-8 DNA in clinical and laboratory specimens.

Suppression of CCR5- but not CXCR4-tropic HIV-1 in lymphoid tissue by human herpesvirus 6

HIV-1 infects target cells via a receptor complex formed by CD4 and a chemokine receptor, primarily CCR5 or CXCR4 (ref. 1). Commonly, HIV-1 transmission is mediated by CCR5-tropic variants, also designated slow/low, non-syncytia-inducer or macrophage-tropic, which dominate the early stages of HIV-1 infection and frequently persist during the entire course of the disease. In contrast, HIV-1 variants that use CXCR4 are typically detected at the later stages, and are associated with a rapid decline in CD4+ T cells and progression to AIDS (refs. 2,7-11). Disease progression is also associated with the emergence of concurrent infections that may affect the course of HIV disease by unknown mechanisms. A lymphotropic agent frequently reactivated in HIV-infected patients is human herpesvirus 6 (HHV-6), which has been proposed as a cofactor in AIDS progression. Here we show that in human lymphoid tissue ex vivo, HHV-6 affects HIV-1 infection in a coreceptor-dependent manner, suppressing CCR5-tropic but not CXCR4-tropic HIV-1 replication, as shown with both uncloned viral isolates and isogenic molecular chimeras. Furthermore, we demonstrate that HHV-6 increases the production of the CCR5 ligand RANTES ('regulated upon activation, normal T-cell expressed and secreted'), the most potent HIV-inhibitory CC chemokine, and that exogenous RANTES mimics the effects of HHV-6 on HIV-1, providing a mechanism for the selective blockade of CCR5-tropic HIV-1. Our data suggest that HHV-6 may profoundly influence the course of HIV-1 infection.

Real-time quantitative PCR for human herpesvirus 6 DNA

The diagnosis of human herpesvirus 6 (HHV-6) infection represents a complex issue because the most widely used diagnostic tools, such as immunoglobulin G antibody titer determination and qualitative DNA PCR with blood cells, are unable to distinguish between latent (clinically silent) and active (often clinically relevant) infection. We have developed a new, highly sensitive, quantitative PCR assay for the accurate measurement of HHV-6 DNA in tissue-derived cell suspensions and body fluids. The test uses a 5' nuclease, fluorogenic assay combined with real-time detection of PCR amplification products with the ABI PRISM 7700 sequence detector system. The sensitivity of this method is equal to the sensitivity of a nested PCR protocol (lower detection limit, 1 viral genome equivalent/test) for both the A and the B HHV-6 subgroups and shows a wider dynamic range of detection (from 1 to 10(6) viral genome equivalents/test) and a higher degree of accuracy, repeatability, and reproducibility compared to those of a standard quantitative-competitive PCR assay developed with the same reference DNA molecule. The novel technique is versatile, showing the same sensitivity and dynamic range with viral DNA extracted from different fluids (i.e., culture medium or plasma) or from tissue-derived cell suspensions. Furthermore, by virtue of its high-throughput format, this method is well suited for large epidemiological surveys.

Coinfection of SCID-hu Thy/Liv mice with human herpesvirus 6 and human immunodeficiency virus type 1

Human herpesvirus 6 (HHV-6) has been proposed as a potential cofactor in the progression of human immunodeficiency virus type 1 (HIV-1) disease. We used the SCID-hu Thy/Liv mouse model to evaluate the in vivo interactions between HHV-6 and HIV-1. Our results demonstrate that HHV-6 and HIV-1 can simultaneously replicate in the human thymus in vivo. In this model, however, the presence of one virus appears not to modify the replication or cytopathicity of the other.

Analysis of serum and plasma beta chemokines in primary HIV infection (PHI)

The levels of certain beta-chemokines in biological fluids do not necessarily reflect their circulating concentrations as they may be dramatically influenced by ex vivo release during sample manipulation. In the present study beta-chemochine levels were evaluated in sequential paired plasma and serum samples collected from a cohort of 18 patients with primary HIV infection (PHI), as well as from 17 HIV-seronegative individuals. In plasma of PHI patients, a significant increase of RANTES (mean 119.1 vs 15.85 ng/ml; p=0.0001) and MIP-1beta (mean 53.4 pg/ml vs 33.6 pg/ml; p=0.0001) was documented. Intra-patient covariance analysis demonstrated no significant association between the variations of RANTES in plasma and serum or between RANTES levels and platelet counts. Reproducibility tests of RANTES measurements in plasma from PHI patients showed a mean coefficient of variation of 1.8%. These data demonstrate that the plasma levels of RANTES and, to a lesser extent, MIP-1beta are persistently perturbed during the early phase of HIV infection. Furthermore they indicate that plasma and serum levels are not directly correlated, being influenced by different physiological phenomena that occur during the ex vivo preparation procedures of the two biological fluids.

CD46 is a cellular receptor for human herpesvirus 6

Human herpesvirus 6 (HHV-6) is the etiologic agent of exanthema subitum, causes opportunistic infections in immunocompromised patients, and has been implicated in multiple sclerosis and in the progression of AIDS. Here, we show that the two major HHV-6 subgroups (A and B) use human CD46 as a cellular receptor. Downregulation of surface CD46 was documented during the course of HHV-6 infection. Both acute infection and cell fusion mediated by HHV-6 were specifically inhibited by a monoclonal antibody to CD46; fusion was also blocked by soluble CD46. Nonhuman cells that were resistant to HHV-6 fusion and entry became susceptible upon expression of recombinant human CD46. The use of a ubiquitous immunoregulatory receptor opens novel perspectives for understanding the tropism and pathogenicity of HHV-6.

Human herpesvirus 6 (HHV-6) causes severe thymocyte depletion in SCID-hu Thy/Liv mice

Human herpesvirus 6 (HHV-6) is a potentially immunosuppressive agent that may act as a cofactor in the progression of AIDS. Here, we describe the first small animal model of HHV-6 infection. HHV-6 subgroup A, strain GS, efficiently infected the human thymic tissue implanted in SCID-hu Thy/Liv mice, leading to the destruction of the graft. Viral DNA was detected in Thy/Liv implants by quantitative polymerase chain reaction (PCR) as early as 4 d after inoculation and peaked at day 14. The productive nature of the infection was confirmed by electron microscopy and immunohistochemical staining. Atypical thymocytes with prominent nuclear inclusions were detected by histopathology. HHV-6 replication was associated with severe, progressive thymocyte depletion involving all major cellular subsets. However, intrathymic T progenitor cells (ITTPs) appeared to be more severely depleted than the other subpopulations, and a preferred tropism of HHV-6 for ITTPs was demonstrated by quantitative PCR on purified thymocyte subsets. These findings suggest that thymocyte depletion by HHV-6 may be due to infection and destruction of these immature T cell precursors. Similar results were obtained with strain PL-1, a primary isolate belonging to subgroup B. The severity of the lesions observed in this animal model underscores the possibility that HHV-6 may indeed be immunosuppressive in humans.

Longitudinal analysis of serum chemokine levels in the course of HIV-1 infection

OBJECTIVES

To investigate the correlation between the serum levels of the CC-chemokines RANTES, macrophage inflammatory protein (MIP)-1alpha and MIP-1beta, and the progression of HIV-1 disease.

DESIGN

Retrospective analysis of serial serum samples from HIV-1 seroconverters selected according to clinical outcome.

METHODS

Twenty-one patients, derived from a cohort recruited between 1985 and 1996 for a prospective study of the natural history of HIV infection, were analysed. All patients had at least one HIV-1-seronegative sample within 1 year prior to the first seropositive test and were followed longitudinally throughout the course of HIV-1 infection (mean follow-up, 73.5 months). Nine were rapid progressors (RP; patients who developed AIDS within 60 months of antibody seroconversion), seven were slow progressors (SP; patients who developed AIDS after 60 months), and five were long-term asymptomatic (LTA; patients with circulating CD4+ cells higher than 400 x 10(6)/l, no signs of HIV disease, no antiretroviral therapy for more than 96 months). A total of 339 serum samples was studied (mean, 16.1 per patient). The levels of RANTES, MIP-1alpha and MIP-1beta were measured by enzyme-linked immunosorbent assay and correlated with different immunological and clinical parameters.

RESULTS

Over the entire follow-up period, the geometric mean of serum RANTES was significantly higher in RP [68.6 ng/ml; 95% confidence interval (CI), 56.9-82.7] than in SP (23.7 ng/ml; 95% CI, 20.0-28.2; P < 0.001) and LTA (19.5 ng/ml; 95% CI, 15.5-24.5; P < 0.001). This difference was already significant during the early clinical stages, when patients had peripheral blood CD4+ cell counts still greater than 400 x 10(6)/l (P < 0.001). By contrast, the mean serum levels of MIP-1alpha and MIP-1beta did not differ significantly between the three study groups. Multivariate analysis using the Cox proportional hazard model demonstrated that the mean serum concentration of RANTES before the development of AIDS was independently associated with the time to AIDS (relative risk, 4.5; 95% CI, 1.1-18.2; P = 0.035). In patients with low versus high mean serum RANTES before the fall of CD4+ cells below 400 x 10(6)/l, the median AIDS-free time was 117.5 and 42.7 months, respectively (P = 0.037).

CONCLUSION

These data suggest that an elevation of serum RANTES predicts a rapid progression of the disease since the early stages of HIV-1 infection.

In vivo evolution of HIV-1 co-receptor usage and sensitivity to chemokine-mediated suppression

Following the identification of the C-C chemokines RANTES, MIP-1alpha and MIP-1beta as major human immunodeficiency virus (HIV)-suppressive factors produced by CD8+ T cells, several chemokine receptors were found to serve as membrane co-receptors for primate immunodeficiency lentiretroviruses. The two most widely used co-receptors thus far recognized, CCR5 and CXCR4, are expressed by both activated T lymphocytes and mononuclear phagocytes. CCR5, a specific RANTES, MIP-1alpha and MIP-1 receptor, is used preferentially by non-MT2-tropic HIV-1 and HIV-2 strains and by simian immunodeficiency virus (SIV), whereas CXCR4, a receptor for the C-X-C chemokine SDF-1, is used by MT2-tropic HIV-1 and HIV-2, but not by SIV. Other receptors with a more restricted cellular distribution, such as CCR2b, CCR3 and STRL33, can also function as co-receptors for selected viral isolates. The third variable region (V3) of the gp120 envelope glycoprotein of HIV-1 has been fingered as a critical determinant of the co-receptor choice. Here, we document a consistent pattern of evolution of viral co-receptor usage and sensitivity to chemokine-mediated suppression in a longitudinal follow-up of children with progressive HIV-1 infection. Viral isolates obtained during the asymptomatic stages generally used only CCR5 as a co-receptor and were inhibited by RANTES, MIP-1alpha and MIP-1beta, but not by SDF-1. By contrast, the majority of the isolates derived after the progression of the disease were resistant to C-C chemokines, having acquired the ability to use CXCR4 and, in some cases, CCR3, while gradually losing CCR5 usage. Surprisingly, most of these isolates were also insensitive to SDF-1, even when used in combination with RANTES. An early acquisition of CXCR4 usage predicted a poor prognosis. In children who progressed to AIDS without a shift to CXCR4 usage, all the sequential isolates were CCR5-dependent but showed a reduced sensitivity to C-C chemokines. Discrete changes in the V3 domain of gp120 were associated with the loss of sensitivity to C-C chemokines and the shift in co-receptor usage. These results suggest an adaptive evolution of HIV-1 in vivo, leading to escape from the control of the antiviral C-C chemokines.

Increased plasma levels of the C-C chemokine RANTES in patients with primary HIV-1 infection

To investigate the role played by chemokines in the natural history of human immunodeficiency virus (HIV) infection, we measured the plasma levels of RANTES. MIP-1 alpha and MIP-1 beta in a cohort of patients with primary HIV-1 infection (PHI) followed longitudinally. The cohort included 17 patients with well-documented history of acute HIV syndrome within two months of the first observation. The mean plasma concentration of RANTES, but not that of MIP-1 alpha or MIP-1 beta, was significantly higher in patients with PHI (192.3 ng/ml) than in five HIV-seronegative controls (8.0 ng/ml) studied during the same time period. Treatment of blood with a cocktail of drugs preventing platelet activation, followed by high-speed centrifugation, reduced the levels of RANTES by approximately 2 logs both in patients and in controls, indicating that the bulk of RANTES was released by platelets, which are known to store this chemokine in their alpha-granules, in the immediate aftermath of blood drawing. No correlation was seen between the levels of RANTES and the number of HIV genome equivalents in plasma. These data suggest that large amounts of pre-formed RANTES are stored in platelets and, possibly, in other blood cells during the early phases of HIV infection. The possible role of this HIV-suppressive chemokine in the control of viral replication during PHI remains to be established.

Peptide sequence requirements for the recognition of HLA-B*2705 by specific natural killer cells

NK clones that were inhibited by target cell expression of HLA-B*2705 displayed peptide-specific recognition of HLA-B*2705. To evaluate the specificity of this recognition, synthetic versions of 14 endogenous ligands of HLA-B*2705 were tested for their ability to provide protection from NK-mediated lysis by binding to surface HLA-B*2705 molecules on RMA-S cells deficient in the transporter for Ag presentation. Several unrelated peptides inhibited lysis by the same NK clones. Despite similar capacities to stabilize HLA-B*2705 molecules on RMA-S cells, the 14 peptides differed widely in their abilities to provide protection. Single amino acid substitutions in both a protective and a nonprotective peptide revealed the importance of residues 7 and 8 in the peptide for recognition by NK clones, thus localizing the peptide influence to a polymorphic region of the alpha-helix of HLA class I molecules known to control discrimination among allelic variants of HLA-B and HLA-C by NK cells.

Peptide sequence requirements for the recognition of HLA-B*2705 by specific natural killer cells

NK clones that were inhibited by target cell expression of HLA-B*2705 displayed peptide-specific recognition of HLA-B*2705. To evaluate the specificity of this recognition, synthetic versions of 14 endogenous ligands of HLA-B*2705 were tested for their ability to provide protection from NK-mediated lysis by binding to surface HLA-B*2705 molecules on RMA-S cells deficient in the transporter for Ag presentation. Several unrelated peptides inhibited lysis by the same NK clones. Despite similar capacities to stabilize HLA-B*2705 molecules on RMA-S cells, the 14 peptides differed widely in their abilities to provide protection. Single amino acid substitutions in both a protective and a nonprotective peptide revealed the importance of residues 7 and 8 in the peptide for recognition by NK clones, thus localizing the peptide influence to a polymorphic region of the alpha-helix of HLA class I molecules known to control discrimination among allelic variants of HLA-B and HLA-C by NK cells.

Molecular clones of the p58 NK cell receptor reveal immunoglobulin-related molecules with diversity in both the extra- and intracellular domains

Recognition of major histocompatibility class I molecules on target cells by natural killer (NK) cells confers selective protection from NK-mediated lysis. Cross-linking of the p58 NK receptor, involved in the recognition of HLA-C alleles, delivers a negative signal that prevents target cell lysis. Molecular cloning of the p58 NK receptor reported here revealed a new member of the immunoglobulin superfamily. Five distinct p58 receptors, with sequence diversity in the immunoglobulin-related domains, were identified in a single individual. All NK clones tested expressed at least one p58 member. Three different types of transmembrane and cytoplasmic domains exist, even among receptors with closely related extracellular domains. These data revealed a repertoire of NK cells with clonally distributed p58 receptors exhibiting diversity in both extracellular and intracellular domains.

Infection of gamma/delta T lymphocytes by human herpesvirus 6: transcriptional induction of CD4 and susceptibility to HIV infection

Human herpesvirus 6 (HHV-6), a T-lymphotropic human herpesvirus, is a potentially immunosuppressive agent that has been suggested to play a role as a cofactor in the natural history of human immunodeficiency virus (HIV) infection. We studied the interactions between HHV-6 and gamma/delta T lymphocytes, a subset of T cells involved in the protective immune response against specific microorganisms. Polyclonal gamma/delta T cell populations, purified from the peripheral blood of healthy adults and activated in vitro with phytohemagglutinin, were exposed to HHV-6, strain GS (subgroup A), at the approximate multiplicity of infection (MOI) of 1. Signs of virus replication were detected as early as 72 h after infection, as documented by immunofluorescence, electron microscopy, and transmission of extracellular virus. Progression of the infection was associated with the appearance of typical cytomorphological changes and, eventually, massive cell death. In contrast, no signs of infection or cytopathic effects were detected after exposure of gamma/delta T lymphocytes to HHV-7, a CD4+ T-lymphotropic virus closely related to HHV-6. Polyclonal gamma/delta T cells displayed cytolytic activity against both autologous and heterologous target cells infected with HHV-6 and maintained this activity for at least 72 h after infection with HHV-6, despite the high MOI used. As previously documented in mature CD8+ alpha/beta T cells and natural killer cells, HHV-6 infection induced gamma/delta T lymphocytes to express de novo CD4 messenger RNA and protein, as detected by reverse transcriptase-polymerase chain reaction and fluorocytometry, respectively. Whereas purified CD4- gamma/delta T cell populations were per se refractory to HIV infection, they became susceptible to productive infection by HIV-1, strain IIIB, after induction of CD4 expression by HHV-6. These results demonstrate that gamma/delta T cells can be directly targeted and killed by a herpesvirus and may have implications for the potential role of HHV-6 in AIDS.

Peptide specificity in the recognition of MHC class I by natural killer cell clones

Recognition by natural killer (NK) cells of major histocompatibility complex (MHC) class I molecules on target cells inhibits NK-mediated lysis. Here, inhibition of NK clones by HLA-B*2705 molecules mutated at single amino acids in the peptide binding site varied among HLA-B*2705-specific NK clones. In addition, a subset of such NK clones was inhibited by only one of several self peptides loaded onto HLA-B*2705 molecules expressed in peptide transporter-deficient cells, showing that recognition was peptide-specific. These data demonstrate that specific self peptides, complexed with MHC class I, provide protection from NK-mediated lysis.

Two processing pathways for the MHC class II-restricted presentation of exogenous influenza virus antigen

The natural Ag influenza virus A was used to test the requirements for the HLA-DR1-restricted presentation of the epitopes 18-29 in the matrix protein and 307-318 in the hemagglutinin protein. CD4+ cytotoxic T cell clones of similar efficiency were used to detect presentation of these two epitopes. Presentation of the matrix epitope by APC pulsed with either inactivated virus particles or purified soluble protein followed the classical pathway in that 1) it required invariant chain expression, 2) it was blocked by inhibition of protein synthesis, and 3) it was dependent on a function(s) encoded in the MHC class II region. These characteristics suggest that peptides corresponding to the matrix epitope can only load onto newly synthesized class II molecules that were targeted to a processing compartment by the invariant chain. In contrast, presentation of the hemagglutinin epitope processed from virus particles followed a different pathway. First, presentation of hemagglutinin was independent of invariant chain expression. Second, a human B lymphoblastoid cell line in which protein synthesis was inhibited for 9 h was still able to present hemagglutinin even at very low doses of Ag. Third, a DR1-transfected mutant B cell line missing the MHC class II region was able to present hemagglutinin. Thus, mature class II alpha beta molecules can acquire immunogenic peptides derived from intact natural Ags for presentation to CD4+ T cells. This pathway may be useful for the binding of peptides derived from Ags that are rapidly degraded upon uptake into APC.

Two processing pathways for the MHC class II-restricted presentation of exogenous influenza virus antigen

The natural Ag influenza virus A was used to test the requirements for the HLA-DR1-restricted presentation of the epitopes 18-29 in the matrix protein and 307-318 in the hemagglutinin protein. CD4+ cytotoxic T cell clones of similar efficiency were used to detect presentation of these two epitopes. Presentation of the matrix epitope by APC pulsed with either inactivated virus particles or purified soluble protein followed the classical pathway in that 1) it required invariant chain expression, 2) it was blocked by inhibition of protein synthesis, and 3) it was dependent on a function(s) encoded in the MHC class II region. These characteristics suggest that peptides corresponding to the matrix epitope can only load onto newly synthesized class II molecules that were targeted to a processing compartment by the invariant chain. In contrast, presentation of the hemagglutinin epitope processed from virus particles followed a different pathway. First, presentation of hemagglutinin was independent of invariant chain expression. Second, a human B lymphoblastoid cell line in which protein synthesis was inhibited for 9 h was still able to present hemagglutinin even at very low doses of Ag. Third, a DR1-transfected mutant B cell line missing the MHC class II region was able to present hemagglutinin. Thus, mature class II alpha beta molecules can acquire immunogenic peptides derived from intact natural Ags for presentation to CD4+ T cells. This pathway may be useful for the binding of peptides derived from Ags that are rapidly degraded upon uptake into APC.

Presentation of cytosolic antigen by HLA-DR requires a function encoded in the class II region of the MHC

The processing pathway for the MHC class II-restricted presentation of endogenous cytosolic Ag is distinct from the class I pathway since a cytosolic form of the influenza virus A hemagglutinin, expressed by a recombinant vaccinia virus, was presented by HLA-DR in a B cell mutant lacking the TAP1 subunit of the transporter for Ag presentation (TAP). In this report, two additional B cell mutants have been used to define the requirements of this TAP1-independent processing pathway. The first mutant, .61, lacks expression of both TAP1 and TAP2 genes, and of both LMP2 and LMP7 genes encoding proteasome subunits. As expected, class I-restricted presentation of the influenza virus matrix protein was totally deficient in mutant .61. In contrast, class II-restricted presentation of both the natural cytosolic matrix and the engineered cytosolic hemagglutinin proteins was functional in mutant .61. Thus, presentation of cytosolic Ag by class II molecules is independent of both TAP subunits and of the two MHC-encoded proteasome subunits. However, this endogenous processing pathway is dependent on at least one other function encoded in the class II region of the MHC as demonstrated with the second mutant, .174, in which a large deletion eliminates all expressed class II genes. Mutant .174 transfected with HLA-DR1 genes was previously shown to be defective in the presentation of exogenous Ag but normal in the presentation of short exogenous peptides. We show here that .174(DR1) is also defective in the presentation of cytosolic matrix and hemagglutinin proteins. This similar requirement for the class II-restricted presentation of either cytosolic Ag or internalized exogenous Ag suggests that both forms of Ag are ultimately targeted to the same cellular compartment for association with class II molecules.

Presentation of cytosolic antigen by HLA-DR requires a function encoded in the class II region of the MHC

The processing pathway for the MHC class II-restricted presentation of endogenous cytosolic Ag is distinct from the class I pathway since a cytosolic form of the influenza virus A hemagglutinin, expressed by a recombinant vaccinia virus, was presented by HLA-DR in a B cell mutant lacking the TAP1 subunit of the transporter for Ag presentation (TAP). In this report, two additional B cell mutants have been used to define the requirements of this TAP1-independent processing pathway. The first mutant, .61, lacks expression of both TAP1 and TAP2 genes, and of both LMP2 and LMP7 genes encoding proteasome subunits. As expected, class I-restricted presentation of the influenza virus matrix protein was totally deficient in mutant .61. In contrast, class II-restricted presentation of both the natural cytosolic matrix and the engineered cytosolic hemagglutinin proteins was functional in mutant .61. Thus, presentation of cytosolic Ag by class II molecules is independent of both TAP subunits and of the two MHC-encoded proteasome subunits. However, this endogenous processing pathway is dependent on at least one other function encoded in the class II region of the MHC as demonstrated with the second mutant, .174, in which a large deletion eliminates all expressed class II genes. Mutant .174 transfected with HLA-DR1 genes was previously shown to be defective in the presentation of exogenous Ag but normal in the presentation of short exogenous peptides. We show here that .174(DR1) is also defective in the presentation of cytosolic matrix and hemagglutinin proteins. This similar requirement for the class II-restricted presentation of either cytosolic Ag or internalized exogenous Ag suggests that both forms of Ag are ultimately targeted to the same cellular compartment for association with class II molecules.

Recognition of virus-infected cells by natural killer cell clones is controlled by polymorphic target cell elements

Natural killer (NK) cells provide a first line of defense against viral infections. The mechanisms by which NK cells recognize and eliminate infected cells are still largely unknown. To test whether target cell elements contribute to NK cell recognition of virus-infected cells, human NK cells were cloned from two unrelated donors and assayed for their ability to kill normal autologous or allogeneic cells before and after infection by human herpesvirus 6 (HHV-6), a T-lymphotropic herpesvirus. Of 132 NK clones isolated from donor 1, all displayed strong cytolytic activity against the NK-sensitive cell line K562, none killed uninfected autologous T cells, and 65 (49%) killed autologous T cells infected with HHV-6. A panel of representative NK clones from donors 1 and 2 was tested on targets obtained from four donors. A wide heterogeneity was observed in the specificity of lysis of infected target cells among the NK clones. Some clones killed none, some killed only one, and others killed more than one of the different HHV-6-infected target cells. Killing of infected targets was not due to complete absence of class I molecules because class I surface levels were only partially affected by HHV-6 infection. Thus, target cell recognition is not controlled by the effector NK cell alone, but also by polymorphic elements on the target cell that restrict NK cell recognition. Furthermore, NK clones from different donors display a variable range of specificities in their recognition of infected target cells.

Infection of natural killer cells by human herpesvirus 6

Natural killer (NK) cells are a functionally defined subset of non-T, non-B lymphocytes of bone marrow origin, which induce lysis of selected target cells, including neoplastic and virus-infected cells. The NK cell function provides an important mechanism of primary defence against viruses in vivo, as demonstrated by the occurrence of multiple herpesvirus infections in patients congenitally lacking NK cells. Here we show that functionally competent CD3- NK clones can be productively infected by human herpesvirus 6 (HHV-6), a T-lymphotropic DNA virus that may play a role in the acquired immunodeficiency syndrome (AIDS) and in the chronic fatigue syndrome, two disorders associated with a defective NK cell activity. The infection is cytopathic and induces de novo expression of CD4, an antigen not expressed within the NK lineage, thereby predisposing NK cells to infection by human immunodeficiency virus type 1 (HIV-1). These results provide evidence that a herpesvirus can directly target and kill NK cells, a potential strategy to suppress the natural anti-viral immunity of the host.

Processing pathways for presentation of cytosolic antigen to MHC class II-restricted T cells

Antigens presented to CD4+ T cells derive primarily from exogenous proteins that are processed into peptides capable of binding to class II major histocompatibility complex (MHC) molecules in an endocytic compartment. In contrast, antigens presented to CD8+ T cells derive mostly from proteins processed in the cytosol, and peptide loading onto class I MHC molecules in an early exocytic compartment is dependent on a transporter for antigen presentation encoded in the class II MHC region. Endogenous cytosolic antigen can also be presented by class II molecules. Here we show that, unlike class I-restricted recognition of antigen, HLA-DR1-restricted recognition of cytosolic antigen occurs in mutant cells without a transporter for antigen presentation. In contrast, DR1-restricted recognition of a short cytosolic peptide is dependent on such a transporter. Thus helper T-cell epitopes can be generated from cytosolic antigens by several mechanisms, one of which is distinct from the classical class I pathway.

Clonal analysis of joint fluid T lymphocytes in patients with juvenile rheumatoid arthritis

Synovial fluid (SF) lymphocytes from 4 patients with pauciarticular juvenile rheumatoid arthritis (JRA) and 4 patients with polyarticular JRA were examined for their phenotypic and functional characteristics. In all 8 patients there was a high proportion of activated SF T cells, together with an increased proportion of CD2+CD3- and the presence of CD3+CD4-CD8-WT31- lymphocytes. The functional analysis at the clonal level in 5 patients (427 clones) showed a relevant proportion of cytotoxic T cell clones, which were not confined to typically cytolytic phenotypes, but were also present among CD3+CD4+CD8- cultures. Compared to those with pauciarticular JRA, patients with polyarticular disease had a significantly higher proportion of T cell clones with cytotoxic activity. Although derived from a limited number of patients, our data suggest a direct involvement of T cells in the pathogenetic mechanisms that originate and maintain the articular damage, and the possibility of different or more pronounced T cell reactivities in the clinically more diffuse JRA types.