Detection of Chimeric Cellular: HIV mRNAs Generated Through Aberrant Splicing in HIV-1 Latently Infected Resting CD4+ T Cells

Latent HIV-1 provirus in infected individuals on suppressive therapy does not always remain transcriptionally silent. Both HIV-1 LTR and human gene promoter derived transcriptional events can contribute HIV-1 sequences to the mRNA produced in the cell. In addition, chimeric cellular:HIV mRNA can arise through readthrough transcription and aberrant splicing. Using target enrichment coupled to the Illumina Mi-Seq and PacBio RS II platforms, we show that 3’ LTR activation is frequent in latently infected cells from both the CCL19-induced primary cell model of HIV-1 latency as well as ex vivo samples. In both systems of latent HIV-1 infection, we detected several chimeric species that were generated via activation of a cryptic splice donor site in the 5’ LTR of HIV-1. Aberrant splicing involving the major HIV-1 splice donor sites, SD1 and SD4 disrupts post-transcriptional processing of the gene in which HIV-1 is integrated. In the primary cell model of HIV-1 latency, Tat-encoding sequences are incorporated into the chimeric mRNA transcripts through the use of SD4. Our study unravels clues to the characteristics of HIV-1 integrants that promote formation of chimeric cellular:HIV mRNA and improves the understanding of the HIV-1 RNA footprint in latently infected cells.

The RNA-Binding Proteins SRP14 and HMGB3 Control HIV-1 Tat mRNA Processing and Translation During HIV-1 Latency

HIV-1 Tat protein is essential for virus production. RNA-binding proteins that facilitate Tat production may be absent or downregulated in resting CD4+ T-cells, the main reservoir of latent HIV in people with HIV (PWH) on antiretroviral therapy (ART). In this study, we examined the role of Tat RNA-binding proteins on the expression of Tat and control of latent and productive infection. Affinity purification coupled with mass spectrometry analysis was used to detect binding partners of MS2-tagged tat mRNA in a T cell-line model of HIV latency. The effect of knockdown and overexpression of the proteins of interest on Tat transactivation and translation was assessed by luciferase-based reporter assays and infections with a dual color HIV reporter virus. Out of the 243 interactions identified, knockdown of SRP14 (Signal Recognition Particle 14) negatively affected tat mRNA processing and translation as well as Tat-mediated transactivation, which led to an increase in latent infection. On the other hand, knockdown of HMGB3 (High Mobility Group Box 3) resulted in an increase in Tat transactivation and translation as well as an increase in productive infection. Footprinting experiments revealed that SRP14 and HMGB3 proteins bind to TIM-TAM, a conserved RNA sequence-structure in tat mRNA that functions as a Tat IRES modulator of tat mRNA. Overexpression of SRP14 in resting CD4+ T-cells from patients on ART was sufficient to reverse HIV-1 latency and induce virus production. The role of SRP14 and HMGB3 proteins in controlling HIV Tat expression during latency will be further assessed as potential drug targets.

Identification of Native and Posttranslationally Modified HLA-B*57:01-Restricted HIV Envelope Derived Epitopes Using Immunoproteomics

The recognition of pathogen-derived peptides by T lymphocytes is the cornerstone of adaptive immunity, whereby intracellular antigens are degraded in the cytosol and short peptides assemble with class I human leukocyte antigen (HLA) molecules in the ER. These peptide-HLA complexes egress to the cell surface and are scrutinized by cytotoxic CD8+ T-cells leading to the eradication of the infected cell. Here, naturally presented HLA-B*57:01 bound peptides derived from the envelope protein of the human immunodeficiency virus (HIVenv) are identified. HIVenv peptides are present at a very small percentage of the overall HLA-B*57:01 peptidome (<0.1%) and both native and posttranslationally modified forms of two distinct HIV peptides are identified. Notably, a peptide bearing a natively encoded C-terminal tryptophan residue is also present in a modified form containing a kynurenine residue. Kynurenine is a major product of tryptophan catabolism and is abundant during inflammation and infection. Binding of these peptides at a molecular level and their immunogenicity in preliminary functional studies are examined. Modest immune responses are observed to the modified HIVenv peptide, highlighting a potential role for kynurenine-modified peptides in the immune response to HIV and other viral infections.

MYB elongation is regulated by the nucleic acid binding of NFκB p50 to the intronic stem-loop region

MYB transcriptional elongation is regulated by an attenuator sequence within intron 1 that has been proposed to encode a RNA stem loop (SLR) followed by a polyU tract. We report that NFκBp50 can bind the SLR polyU RNA and promote MYB transcriptional elongation together with NFκBp65. We identified a conserved lysine-rich motif within the Rel homology domain (RHD) of NFκBp50, mutation of which abrogated the interaction of NFκBp50 with the SLR polyU and impaired NFκBp50 mediated MYB elongation. We observed that the TAR RNA-binding region of Tat is homologous to the NFκBp50 RHD lysine-rich motif, a finding consistent with HIV Tat acting as an effector of MYB transcriptional elongation in an SLR dependent manner. Furthermore, we identify the DNA binding activity of NFκBp50 as a key component required for the SLR polyU mediated regulation of MYB. Collectively these results suggest that the MYB SLR polyU provides a platform for proteins to regulate MYB and reveals novel nucleic acid binding properties of NFκBp50 required for MYB regulation.

Silent mutations at codons 65 and 66 in reverse transcriptase alleviate indel formation and restore fitness in subtype B HIV-1 containing D67N and K70R drug resistance mutations

Resistance to combined antiretroviral therapy (cART) in HIV-1-infected individuals is typically due to nonsynonymous mutations that change the protein sequence; however, the selection of synonymous or ‘silent’ mutations in the HIV-1 genome with cART has been reported. These silent K65K and K66K mutations in the HIV-1 reverse transcriptase (RT) occur in over 35% of drug-experienced individuals and are highly associated with the thymidine analog mutations D67N and K70R, which confer decreased susceptibility to most nucleoside and nucleotide RT inhibitors. However, the basis for selection of these silent mutations under selective drug pressure is unknown. Using Illumina next-generation sequencing, we demonstrate that the D67N/K70R substitutions in HIV-1 RT increase indel frequency by 100-fold at RT codons 65–67, consequently impairing viral fitness. Introduction of either K65K or K66K into HIV-1 containing D67N/K70R reversed the error-prone DNA synthesis at codons 65–67 in RT and improved viral replication fitness, but did not impact RT inhibitor drug susceptibility. These data provide new mechanistic insights into the role of silent mutations selected during antiretroviral therapy and have broader implications for the relevance of silent mutations in the evolution and fitness of RNA viruses.

Vaginal concentrations of lactic acid potently inactivate HIV

OBJECTIVES

When Lactobacillus spp. dominate the vaginal microbiota of women of reproductive age they acidify the vagina to pH <4.0 by producing ∼1% lactic acid in a nearly racemic mixture of d- and l-isomers. We determined the HIV virucidal activity of racemic lactic acid, and its d- and l-isomers, compared with acetic acid and acidity alone (by the addition of HCl).

METHODS

HIV-1 and HIV-2 were transiently treated with acids in the absence or presence of human genital secretions at 37°C for different time intervals, then immediately neutralized and residual infectivity determined in the TZM-bl reporter cell line.

RESULTS

l-lactic acid at 0.3% (w/w) was 17-fold more potent than d-lactic acid in inactivating HIVBa-L. Complete inactivation of different HIV-1 subtypes and HIV-2 was achieved with ≥0.4% (w/w) l-lactic acid. At a typical vaginal pH of 3.8, l-lactic acid at 1% (w/w) more potently and rapidly inactivated HIVBa-L and HIV-1 transmitter/founder strains compared with 1% (w/w) acetic acid and with acidity alone, all adjusted to pH 3.8. A final concentration of 1% (w/w) l-lactic acid maximally inactivated HIVBa-L in the presence of cervicovaginal secretions and seminal plasma. The anti-HIV activity of l-lactic acid was pH dependent, being abrogated at neutral pH, indicating that its virucidal activity is mediated by protonated lactic acid and not the lactate anion.

CONCLUSIONS

l-lactic acid at physiological concentrations demonstrates potent HIV virucidal activity distinct from acidity alone and greater than acetic acid, suggesting a protective role in the sexual transmission of HIV.

Phosphatidylethanolamine binding is a conserved feature of cyclotide-membrane interactions

Cyclotides are bioactive cyclic peptides isolated from plants that are characterized by a topologically complex structure and exceptional resistance to enzymatic or thermal degradation. With their sequence diversity, ultra-stable core structural motif, and range of bioactivities, cyclotides are regarded as a combinatorial peptide template with potential applications in drug design. The mode of action of cyclotides remains elusive, but all reported biological activities are consistent with a mechanism involving membrane interactions. In this study, a diverse set of cyclotides from the two major subfamilies, Möbius and bracelet, and an all-d mirror image form, were examined to determine their mode of action. Their lipid selectivity and membrane affinity were determined, as were their toxicities against a range of targets (red blood cells, bacteria, and HIV particles). Although they had different membrane-binding affinities, all of the tested cyclotides targeted membranes through binding to phospholipids containing phosphatidylethanolamine headgroups. Furthermore, the biological potency of the tested cyclotides broadly correlated with their ability to target and disrupt cell membranes. The finding that a broad range of cyclotides target a specific lipid suggests their categorization as a new lipid-binding protein family. Knowledge of their membrane specificity has the potential to assist in the design of novel drugs based on the cyclotide framework, perhaps allowing the targeting of peptide drugs to specific cell types.

Decoding the membrane activity of the cyclotide kalata B1: the importance of phosphatidylethanolamine phospholipids and lipid organization on hemolytic and anti-HIV activities

Cyclotides, a large family of cyclic peptides from plants, have a broad range of biological activities, including insecticidal, cytotoxic, and anti-HIV activities. In all of these activities, cell membranes seem likely to be the primary target for cyclotides. However, the mechanistic role of lipid membranes in the activity of cyclotides remains unclear. To determine the role of lipid organization in the activity of the prototypic cyclotide, kalata B1 (kB1), and synthetic analogs, their bioactivities and affinities for model membranes were evaluated. We found that the bioactivity of kB1 is dependent on the lipid composition of target cell membranes. In particular, the activity of kB1 requires specific interactions with phospholipids containing phosphatidylethanolamine (PE) headgroups but is further modulated by nonspecific peptide-lipid hydrophobic interactions, which are favored in raft-like membranes. Negatively charged phospholipids do not favor high kB1 affinity. This lipid selectivity explains trends in antimicrobial and hemolytic activities of kB1; it does not target bacterial cell walls, which are negatively charged and lacking PE-phospholipids but can insert in the membranes of red blood cells, which have a low PE content and raft domains in their outer layer. We further show that the anti-HIV activity of kB1 is the result of its ability to target and disrupt the membranes of HIV particles, which are raft-like membranes very rich in PE-phospholipids.

Structure activity relationship of dendrimer microbicides with dual action antiviral activity

BACKGROUND

Topical microbicides, used by women to prevent the transmission of HIV and other sexually transmitted infections are urgently required. Dendrimers are highly branched nanoparticles being developed as microbicides. However, the anti-HIV and HSV structure-activity relationship of dendrimers comprising benzyhydryl amide cores and lysine branches, and a comprehensive analysis of their broad-spectrum anti-HIV activity and mechanism of action have not been published.

METHODS AND FINDINGS

Dendrimers with optimized activity against HIV-1 and HSV-2 were identified with respect to the number of lysine branches (generations) and surface groups. Antiviral activity was determined in cell culture assays. Time-of-addition assays were performed to determine dendrimer mechanism of action. In vivo toxicity and HSV-2 inhibitory activity were evaluated in the mouse HSV-2 susceptibility model. Surface groups imparting the most potent inhibitory activity against HIV-1 and HSV-2 were naphthalene disulfonic acid (DNAA) and 3,5-disulfobenzoic acid exhibiting the greatest anionic charge and hydrophobicity of the seven surface groups tested. Their anti-HIV-1 activity did not appreciably increase beyond a second-generation dendrimer while dendrimers larger than two generations were required for potent anti-HSV-2 activity. Second (SPL7115) and fourth generation (SPL7013) DNAA dendrimers demonstrated broad-spectrum anti-HIV activity. However, SPL7013 was more active against HSV and blocking HIV-1 envelope mediated cell-to-cell fusion. SPL7013 and SPL7115 inhibited viral entry with similar potency against CXCR4-(X4) and CCR5-using (R5) HIV-1 strains. SPL7013 was not toxic and provided at least 12 h protection against HSV-2 in the mouse vagina.

CONCLUSIONS

Dendrimers can be engineered with optimized potency against HIV and HSV representing a unique platform for the controlled synthesis of chemically defined multivalent agents as viral entry inhibitors. SPL7013 is formulated as VivaGel(R) and is currently in clinical development to provide protection against HIV and HSV. SPL7013 could also be combined with other microbicides.

HIV-1 infection induces changes in expression of cellular splicing factors that regulate alternative viral splicing and virus production in macrophages

BACKGROUND

Macrophages are important targets and long-lived reservoirs of HIV-1, which are not cleared of infection by currently available treatments. In the primary monocyte-derived macrophage model of infection, replication is initially productive followed by a decline in virion output over ensuing weeks, coincident with a decrease in the levels of the essential viral transactivator protein Tat. We investigated two possible mechanisms in macrophages for regulation of viral replication, which appears to be primarily regulated at the level of tat mRNA: 1) differential mRNA stability, used by cells and some viruses for the rapid regulation of gene expression and 2) control of HIV-1 alternative splicing, which is essential for optimal viral replication.

RESULTS

Following termination of transcription at increasing times after infection in macrophages, we found that tat mRNA did indeed decay more rapidly than rev or nef mRNA, but with similar kinetics throughout infection. In addition, tat mRNA decayed at least as rapidly in peripheral blood lymphocytes. Expression of cellular splicing factors in uninfected and infected macrophage cultures from the same donor showed an inverse pattern over time between enhancing factors (members of the SR family of RNA binding proteins) and inhibitory factors (members of the hnRNP family). While levels of the SR protein SC35 were greatly up-regulated in the first week or two after infection, hnRNPs of the A/B and H groups were down-regulated. Around the peak of virus production in each culture, SC35 expression declined to levels in uninfected cells or lower, while the hnRNPs increased to control levels or above. We also found evidence for increased cytoplasmic expression of SC35 following long-term infection.

CONCLUSION

While no evidence of differential regulation of tat mRNA decay was found in macrophages following HIV-1 infection, changes in the balance of cellular splicing factors which regulate alternative viral pre-mRNA splicing were observed. These changes correlated with changes in Tat expression and virus production and could play an important role in viral persistence in macrophages. This mechanism could provide a novel target for control of infection in this critical cell type, which would be necessary for eventual eradication of the virus from infected individuals.

Primary T-lymphocytes rescue the replication of HIV-1 DIS RNA mutants in part by facilitating reverse transcription

The dimerization initiation site (DIS) stem-loop within the HIV-1 RNA genome is vital for the production of infectious virions in T-cell lines but not in primary cells. In comparison to peripheral blood mononuclear cells (PBMCs), which can support the replication of both wild type and HIV-1 DIS RNA mutants, we have found that DIS RNA mutants are up to 100 000-fold less infectious than wild-type HIV-1 in T-cell lines. We have also found that the cell-type-dependent replication of HIV-1 DIS RNA mutants is largely producer cell-dependent, with mutants displaying a greater defect in viral cDNA synthesis when viruses were not derived from PBMCs. While many examples exist of host–pathogen interplays that are mediated via proteins, analogous examples which rely on nucleic acid triggers are limited. Our data provide evidence to illustrate that primary T-lymphocytes rescue, in part, the replication of HIV-1 DIS RNA mutants through mediating the reverse transcription process in a cell-type-dependent manner. Our data also suggest the presence of a host cell factor that acts within the virus producer cells. In addition to providing an example of an RNA-mediated cell-type-dependent block to viral replication, our data also provides evidence which help to resolve the dilemma of how HIV-1 genomes with mismatched DIS sequences can recombine to generate chimeric viral RNA genomes.

Asn 362 in gp120 contributes to enhanced fusogenicity by CCR5-restricted HIV-1 envelope glycoprotein variants from patients with AIDS

BACKGROUND

CCR5-restricted (R5) human immunodeficiency virus type 1 (HIV-1) variants cause CD4+ T-cell loss in the majority of individuals who progress to AIDS, but mechanisms underlying the pathogenicity of R5 strains are poorly understood. To better understand envelope glycoprotein (Env) determinants contributing to pathogenicity of R5 viruses, we characterized 37 full-length R5 Envs from cross-sectional and longitudinal R5 viruses isolated from blood of patients with asymptomatic infection or AIDS, referred to as pre-AIDS (PA) and AIDS (A) R5 Envs, respectively.

RESULTS

Compared to PA-R5 Envs, A-R5 Envs had enhanced fusogenicity in quantitative cell-cell fusion assays, and reduced sensitivity to inhibition by the fusion inhibitor T-20. Sequence analysis identified the presence of Asn 362 (N362), a potential N-linked glycosylation site immediately N-terminal to CD4-binding site (CD4bs) residues in the C3 region of gp120, more frequently in A-R5 Envs than PA-R5 Envs. N362 was associated with enhanced fusogenicity, faster entry kinetics, and increased sensitivity of Env-pseudotyped reporter viruses to neutralization by the CD4bs-directed Env mAb IgG1b12. Mutagenesis studies showed N362 contributes to enhanced fusogenicity of most A-R5 Envs. Molecular models indicate N362 is located adjacent to the CD4 binding loop of gp120, and suggest N362 may enhance fusogenicity by promoting greater exposure of the CD4bs and/or stabilizing the CD4-bound Env structure.

CONCLUSION

Enhanced fusogenicity is a phenotype of the A-R5 Envs studied, which was associated with the presence of N362, enhanced HIV-1 entry kinetics and increased CD4bs exposure in gp120. N362 contributes to fusogenicity of R5 Envs in a strain dependent manner. Our studies suggest enhanced fusogenicity of A-R5 Envs may contribute to CD4+ T-cell loss in subjects who progress to AIDS whilst harbouring R5 HIV-1 variants. N362 may contribute to this effect in some individuals.

CD16+ monocyte subset preferentially harbors HIV-1 and is expanded in pregnant Malawian women with Plasmodium falciparum malaria and HIV-1 infection

In a cross-sectional study, monocyte subsets in placental, cord, and maternal peripheral blood from pregnant Malawian women with human immunodeficiency virus (HIV)-1 infection and/or malaria were analyzed. HIV-uninfected Malawian women had higher baseline proportions of CD16(+) monocytes than those reported for healthy adults in developed countries. Malaria was associated with an increase in the proportion of CD16(+) monocytes that was significant in women coinfected with HIV-1. CD16(+) monocytes expressed higher CCR5 levels than did CD14(hi)/CD16(-) monocytes and were significantly more likely to harbor HIV-1. These data suggest a role for CD16(+) monocytes in the pathogenesis of maternal malaria and HIV-1 infections.

The CD16+Monocyte Subset Is More Permissive to Infection and Preferentially Harbors HIV-1 In Vivo

HIV-1 persists in peripheral blood monocytes in individuals receiving highly active antiretroviral therapy (HAART) with viral suppression, despite these cells being poorly susceptible to infection in vitro. Because very few monocytes harbor HIV-1 in vivo, we considered whether a subset of monocytes might be more permissive to infection. We show that a minor CD16+ monocyte subset preferentially harbors HIV-1 in infected individuals on HAART when compared with the majority of monocytes (CD14highCD16-). We confirmed this by in vitro experiments showing that CD16+ monocytes were more susceptible to CCR5-using strains of HIV-1, a finding that is associated with higher CCR5 expression on these cells. CD16+ monocytes were also more permissive to infection with a vesicular stomatitis virus G protein-pseudotyped reporter strain of HIV-1 than the majority of monocytes, suggesting that they are better able to support HIV-1 replication after entry. Consistent with this observation, high molecular mass complexes of apolipoprotein B mRNA-editing enzyme, catalytic polypeptide-like 3G (APOBEC3G) were observed in CD16+ monocytes that were similar to those observed in highly permissive T cells. In contrast, CD14highCD16- monocytes contained low molecular mass active APOBEC3G, suggesting this is a mechanism of resistance to HIV-1 infection in these cells. Collectively, these data show that CD16+ monocytes are preferentially susceptible to HIV-1 entry, more permissive for replication, and constitute a continuing source of viral persistence during HAART.

SerpinB2 Is an Inducible Host Factor Involved in Enhancing HIV-1 Transcription and Replication

The serine protease inhibitor SerpinB2 (plasminogen activator inhibitor-2) is a major product of activated monocytes and macrophages and is substantially induced during most inflammatory processes. Distinct from its widely described extracellular role as an inhibitor of urokinase plasminogen activator, SerpinB2 has recently been shown to have an intracellular role as a retinoblastoma protein (Rb)-binding protein that inhibits Rb degradation. Here we show that HIV-1 infection and gp120 treatment of human peripheral blood mononuclear cells resulted in induction of SerpinB2. Furthermore, SerpinB2 expression in THP-1 monocyte/macrophage, Jurkat T, and HeLa cell lines increased replication of HIV-1 and enhanced transcription from the HIV-1 long terminal repeat (LTR) promoter by 3-10-fold. Increased HIV-1 gene expression and transcription was also observed in activated macrophages from SerpinB2+/+ mice compared with macrophages from SerpinB2-/- mice. The SerpinB2-mediated elevation of Rb protein levels appeared to be responsible for enhancing transcription from the core promoter region of the LTR by relieving HDM2-mediated inhibition of Sp1 and/or by increasing the Sp1/Sp3 expression ratios. This is the first report associating HIV-1 replication with SerpinB2 expression and illustrates that SerpinB2 is a potentially important inducible host factor that significantly promotes HIV-1 replication.

Use of laser capture microdissection to detect integrated HIV-1 DNA in macrophages and astrocytes from autopsy brain tissues

The importance of astrocytes as a reservoir of human immunodeficiency virus type 1 (HIV-1) in the brain remains elusive. By combining immunohistochemistry, laser capture microdissection, and triple-nested Alu-PCR, we demonstrate integrated HIV-1 in astrocytes and macrophages isolated directly from autopsy brain tissues of HIV-1-infected subjects. The ability of HIV-1 to integrate in terminally differentiated astrocytes suggests a permanent reservoir of provirus in brain that will impact the development and likely success of strategies aimed at eradicating HIV-1.

Normal CD16 expression and phagocytosis of Mycobacterium avium complex by monocytes from a current cohort of HIV-1-infected patients

Monocyte phenotype and function were measured in whole blood sampled from a current cohort of human immunodeficiency virus (HIV)-infected individuals attending a large, metropolitan, university-affiliated hospital. There was no significant difference in the prevalence of CD16+ monocytes or the capacity of monocytes to ingest heat-killed Mycobacterium avium complex between these individuals and HIV-uninfected control subjects, regardless of viral load, current CD4+ T cell count, nadir CD4+ T cell count, or time since diagnosis of HIV infection. CD16+ monocyte prevalence was, however, elevated in patients not currently receiving antiretroviral therapy. We conclude that HIV type 1 infection in the setting of highly active antiretroviral therapy is associated with normal monocyte function and phenotype.

Isolation of human immunodeficiency virus type 1 from peripheral blood monocytes

Human immunodeficiency virus type 1 (HIV-1) can infect circulating peripheral blood monocytes and resting CD4+ T lymphocytes despite sustained suppression of plasma viremia to undetectable levels. These persistently infected cell populations pose a barrier for virus eradication by highly active antiretroviral therapy (HAART), and are a significant reservoir of HIV-1 contributing to viral rebound following cessation or failure of HAART. This chapter provides a protocol for isolating replication-competent HIV-1 from peripheral blood monocytes of HIV-1-infected individuals, including those with sustained plasma HIV-1 RNA levels below 50 copies/mL, by co-culture with CD8-depleted, phytohemagglutinin-activated donor peripheral blood mononuclear cells. In our laboratory, this protocol has the sensitivity to achieve a success rate of positive HIV-1 isolation in approx 70% of cases. The study of HIV-1 strains harbored by peripheral blood monocytes of patients undergoing HAART will contribute to the understanding of viral persistence in cellular reservoirs that impede effective HAART.

Mutations that abrogate human immunodeficiency virus type 1 reverse transcriptase dimerization affect maturation of the reverse transcriptase heterodimer

The specific impact of mutations that abrogate human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) dimerization on virus replication is not known, as mutations shown previously to inhibit RT dimerization also impact Gag-Pol stability, resulting in pleiotropic effects on HIV-1 replication. We have previously characterized mutations at codon 401 in the HIV-1 RT tryptophan repeat motif that abrogate RT dimerization in vitro, leading to a loss in polymerase activity. The introduction of the RT dimerization-inhibiting mutations W401L and W401A into HIV-1 resulted in the formation of noninfectious viruses with reduced levels of both virion-associated and intracellular RT activity compared to the wild-type virus and the W401F mutant, which does not inhibit RT dimerization in vitro. Steady-state levels of the p66 and p51 RT subunits in viral lysates of the W401L and W401A mutants were reduced, but no significant decrease in Gag-Pol was observed compared to the wild type. In contrast, there was a decrease in processing of p66 to p51 in cell lysates for the dimerization-defective mutants compared to the wild type. The treatment of transfected cells with indinavir suggested that the HIV-1 protease contributed to the degradation of virion-associated RT subunits. These data demonstrate that mutations near the RT dimer interface that abrogate RT dimerization in vitro result in the production of replication-impaired viruses without detectable effects on Gag-Pol stability or virion incorporation. The inhibition of RT activity is most likely due to a defect in RT maturation, suggesting that RT dimerization represents a valid drug target for chemotherapeutic intervention.

Mutational analysis of the HIV-1 LTR as a promoter of negative sense transcription

The HIV-1 gene promoter is a bi-directional promoter of transcription. We report the characterization of the negative sense promoter (NSP) by analysis of the effect on negative sense transcription of a series of LTR U3 region substitution mutants. Mutations in the region nt -58 to -183 (positive sense transcription initiation nt +1) reduced transcription to <15% of wild type NSP activity. This region, essential for NSP activity, was designated the core basal promoter. Over expression of NF-kappaB RelA(p65) and LEF-1 increased negative sense expression, as did over expression of H-ras oncogene, consistent with the presence of cognate sequence motifs for NF-kappaB, LEF-1 and RBF. We were also able to confirm that the NSP is a TATA-less promoter inhibited by HIV-1 Tat. Based on our findings, we propose a model for the interaction between the NSP and PSP, and the role of Tat in regulating the interaction.

Selectively reduced tat mRNA heralds the decline in productive human immunodeficiency virus type 1 infection in monocyte-derived macrophages

The transcription and splicing of human immunodeficiency virus type 1 (HIV-1) mRNA in primary blood monocyte-derived macrophages (MDM) and CD4(+) peripheral blood lymphocytes (PBL) were compared to determine whether any differences might account for the slower noncytopathic infection of cells of the macrophage lineage. The expression of regulatory mRNAs during acute infection of MDM was delayed by about 12 h compared to that of PBL. In each cell type, an increase in spliced viral mRNAs slightly preceded virus production from the culture. Following the peak of productive infection, there was a proportional decrease in the expression of all regulatory mRNAs detected in PBL. In MDM, a dramatic additional decrease specifically in the tat mRNA species heralded a reduction in virus production. This decline in tat mRNA was reflected by a concomitant decrease in Tat activity in the cells and occurred with the same kinetics irrespective of the age of the cells when infected. Addition of exogenous Tat protein elicited a burst of virus production from persistently infected MDM, suggesting that the decrease in virus production from the cultures is a consequence of the reduction in tat mRNA levels. Our results show that modulation of HIV-1 mRNAs in macrophages during long-term infection, which is dependent on the period of infection rather than cell differentiation or maturation, results in a selective reduction of Tat protein levels at the commencement of a persistent, less productive phase of infection. Determination of the mechanism of this mRNA modulation may lead to novel targets for control of replication in these important viral reservoirs.

Monocytes harbour replication-competent, non-latent HIV-1 in patients on highly active antiretroviral therapy

OBJECTIVE

To determine whether HIV-1 can be recovered from blood monocytes as well as resting, memory CD4 T lymphocytes of patients on highly active antiretroviral therapy (HAART) with undetectable plasma viraemia and whether infection is active or latent.

DESIGN

Five patients with plasma HIV-1-RNA levels of less than 500 copies/ml for at least 3 months and less than 50 copies/ml at the time of sampling were initially selected, followed by an additional five patients with viral loads of less than 50 copies/ml for 3 months or more.

METHODS

Monocytes were isolated from blood by plastic adherence, then further purified by a second adherence step or CD3 depletion before co-culture with CD8-depleted donor peripheral blood mononuclear cells. Virus isolates were examined for mutations conferring resistance to reverse transcriptase or protease inhibitors and for genotype. The highly purified monocytes were also analysed for the presence of proviral and unintegrated viral DNA and multiply spliced (MS) viral mRNA by polymerase chain reaction.

RESULTS

Virus was recovered from monocytes of five patients. Sequencing of the recovered viruses did not reveal multiple drug resistance, and was consistent with a non-syncytium-inducing/CCR5 phenotype. Proviral DNA was detectable in monocytes from all subjects, and unintegrated HIV-1 DNA and MS RNA was found in four out of five populations examined.

CONCLUSION

Recovery of replication-competent virus from some HAART patients indicates that monocytes can also harbour HIV-1. Detection of circular, viral DNA and spliced RNA, albeit at very low levels, in these cells suggests that their infection is recent and transcriptionally active rather than latent.

HIV-1 can be recovered from a variety of cells including peripheral blood monocytes of patients receiving highly active antiretroviral therapy: a further obstacle to eradication

During highly active antiretroviral therapy (HAART), HIV-1 can still persist in circulating, resting CD4+ T lymphocytes, lymph node mononuclear cells, and seminal cells of patients despite sustained suppression of plasma viremia to undetectable levels. Sanctuary sites where antiretroviral drug penetration is not optimal may allow local HIV-1 infection of cells within and passing through these tissues. Factors such as imperfect drug adherence due to complicated drug regimens may also result in tissue compartments with suboptimal drug concentrations allowing viral replication. We have examined blood monocytes from HIV-1-infected subjects being effectively treated with HAART to determine virus carriage in these cells. Monocytes were purified from peripheral blood of patients with plasma HIV-1 RNA below 50 copies/mL and who had maintained levels of plasma RNA below detection for 3 months or more. Replication-competent virus could be recovered from the majority of monocyte populations by co-culture with CD8-depleted, PHA-activated, peripheral blood mononuclear cells. Sequencing of the reverse transcriptase and protease genes of the recovered viruses did not reveal resistance to both reverse transcriptase and protease inhibitors. Continued new infection of this transitory, circulating population of cells even during prolonged, effective HAART most likely reflects ongoing, low-level HIV-1 replication within cellular reservoirs and sanctuary sites in the body.

Granulocyte-macrophage colony-stimulating factor inhibits HIV-1 replication in monocyte-derived macrophages

BACKGROUND

Previous studies of the effect of granulocyte-macrophage colony-stimulating factor (GM-CSF) on HIV-1 replication in macrophages have had inconsistent results, variously reporting no effect, augmentation or inhibition of viral replication.

OBJECTIVE

To investigate the regulation of HIV-1 in monocyte-derived macrophages (MDM) by GM-CSF in vitro.

METHODS

The role of GM-CSF on HIV-1 replication was assessed as supernatant and intracellular p24 antigen concentrations and by HIV-1 DNA and mRNA production under different culture conditions. Expression of CD4 and CCR5 receptors was examined. The effect of GM-CSF with an E21R mutation, which binds only to the alpha-chain of GM-CSF receptor, was used as an additional control.

RESULTS

GM-CSF consistently suppressed HIV-1 replication in human MDM in vitro, as assessed by supernatant and intracellular p24 antigen concentrations and HIV-1 gag mRNA expression. The inhibitory effect of GM-CSF on HIV-1 replication was observed regardless of HIV-1 strain, source of GM-CSF, stage of MDM maturation or timing of GM-CSF exposure in relation to HIV-1 infection. The effect was dose dependent and reversed by addition of a neutralizing monoclonal antibody (4D4). Flow cytometric analysis of surface expression of CD4 and CCR5 indicates that GM-CSF does not affect HIV-1 entry into MDM. Analysis of intracellular HIV-1 DNA and mRNA suggests that HIV-1 replication is inhibited at or before transcription. E21R GM-CSF had no effect on HIV-1 replication in MDM.

CONCLUSIONS

GM-CSF regulates HIV-1 replication in MDM, inhibiting HIV-1 replication through binding to the beta-chain of the GM-CSF receptor.

Specificity of binding of HIV-1 anti-p24 antibodies to CD4+ lymphocytes from HIV-infected subjects

The clinical utility of a flow cytometric assay (FCA) for intracellular HIV p24 antigen was evaluated in a group of HIV-1-infected subjects. A previously described method, p24-FCA (1), was modified to minimize nonspecific staining and to include irrelevant isotype-matched control antibodies. Blood mononuclear cells from 32 HIV-1 seropositive subjects and 14 HIV-1 seronegative controls were examined. In HIV-1 seropositive individuals, the proportion of CD4+ lymphocytes that bound the p24 monoclonal and the isotype control antibodies were not different. The frequency of cells binding p24 antibodies increased with declining CD4 counts and was highest in patients with low CD4+ lymphocyte counts. Although results of p24-FCA do reflect disease progression, the high nonspecific binding of monoclonal antibodies in infected subjects obscures specific p24 binding and precludes its use as an accurate measure of infection within single cells.

HIV-1 DNA and mRNA concentrations are similar in peripheral blood monocytes and alveolar macrophages in HIV-1-infected individuals

OBJECTIVE

To determine the relative contribution of alveolar macrophages, peripheral blood monocytes (PBM) and peripheral blood lymphocytes (PBL) from HIV-infected individuals to HIV-1 viral load.

METHODS

Alveolar macrophages were obtained by flexible bronchoscopy, and PBM and PBL by venipuncture from HIV-1-infected individuals. Alveolar macrophages and PBM were purified using immunomagnetic bead selection to deplete CD3+ and CD19+ cells from bronchoalveolar lavage and peripheral blood mononuclear cells, respectively. DNA and mRNA were extracted and gag copy number quantified using polymerase chain reaction (PCR) and reverse transcriptase PCR. The titres of infectious cell-associated HIV-1 in cells were determined by the endpoint dilution coculture technique for alveolar macrophages and PBM.

RESULTS

Alveolar macrophages and PBM from HIV-1-infected subjects (n=11) contained equivalent concentrations of HIV-1 DNA and HIV-1 mRNA as determined by PCR and reverse transcriptase PCR, respectively. Antiretroviral therapy was associated with reduced viral DNA concentrations in alveolar macrophages but not in PBM. PBL had a significantly higher level of proviral DNA and mRNA than alveolar macrophages or PBM.

CONCLUSIONS

Although alveolar macrophages infected in vitro are more permissive for HIV-1 replication than PBM, this difference could not be demonstrated in vivo.

Surface CD4 is critical to in vitro HIV infection of human alveolar macrophages

The CD4 glycoprotein is the major cellular receptor for HIV. CD4 surface expression of monocytes decreases with time in culture while their susceptibility to HIV-1 increases. Our aim was to investigate whether this phenomenon occurs in macrophages that have differentiated in vivo by investigating CD4 expression and HIV-1 infection of human alveolar macrophages (AMs). Using flow cytometry to detect CD4 expression by Leu-3a labeled indirectly with fluorescein isothiocyanate or allophycocyanin, we found that CD4 was expressed at low but detectable levels, despite the high background autofluorescence well described in AMs. This finding was supported by the detection of CD4 mRNA in AMs using RT-PCR. T cell contamination of mRNA extracts of AMs was excluded by amplifying in parallel with primers to the constant region of the T cell receptor. Despite this low level of surface CD4, recombinant soluble CD4 and anti-CD4 antibody completely inhibited HIV-1 infection of AMs. We conclude that CD4, although expressed at low levels on the surface of AMs, appears to be critical to HIV-1 infection of these cells.

Human immunodeficiency virus type 1 replication is blocked prior to reverse transcription and integration in freshly isolated peripheral blood monocytes

Peripheral blood monocytes are resistant to productive human immunodeficiency virus type 1 (HIV-1) infection in vitro immediately after isolation. No viral cDNA (either early or late transcripts) was detected by PCR in monocytes exposed to virus on the day of isolation. In contrast, in monocytes cultured for as little as 1 day, initiated and completed reverse transcripts were readily detectable within 24 h of infection with both HIV-1(Ba-L) and primary isolates. The levels of initiated, partially completed, and completed viral DNA copies found 24 h after infection increased progressively with time in culture before infection. Unlike quiescent T lymphocytes, there appeared to be no block or delay in the integration of viral DNA into the genome of susceptible cultured monocytes. With an Alu-PCR method designed to specifically detect proviral DNA being used, integration events were found within 24 h of infection in monocytes cultured for a day or more after isolation. No integration signal was found in freshly isolated monocytes up to 7 days following exposure to the virus. Cloning and sequencing of Alu-PCR-amplified DNA confirmed integration in HIV-1-infected cultured monocytes. Our finding that in vitro replication of HIV-1 is clearly blocked prior to the initiation of reverse transcription in freshly isolated peripheral blood monocytes suggests that these cells may not be susceptible to infection in vivo. Further studies to clarify this possibility and the nature of the block to infection should provide useful information for treatment strategies against HIV-1.

Genomic structure of an attenuated quasi species of HIV-1 from a blood transfusion donor and recipients

A blood donor infected with human immunodeficiency virus-type 1 (HIV-1) and a cohort of six blood or blood product recipients infected from this donor remain free of HIV-1-related disease with stable and normal CD4 lymphocyte counts 10 to 14 years after infection. HIV-1 sequences from either virus isolates or patient peripheral blood mononuclear cells had similar deletions in the nef gene and in the region of overlap of nef and the U3 region of the long terminal repeat (LTR). Full-length sequencing of one isolate genome and amplification of selected HIV-1 genome regions from other cohort members revealed no other abnormalities of obvious functional significance. These data show that survival after HIV infection can be determined by the HIV genome and support the importance of nef or the U3 region of the LTR in determining the pathogenicity of HIV-1.

Susceptibility of human monocytes to HIV type 1 infection in vitro is not dependent on their level of CD4 expression

Monocytes from HIV-seronegative persons were analyzed for CD4 expression and susceptibility to infection with HIV-1 on the day of isolation and following 1, 2, and 7 days in culture. Although surface CD4 was readily detected on freshly isolated monocytes, these cells were relatively resistant to infection. After 1 to 2 days in culture, when surface expression of CD4 had decreased over 90% to near background levels, cells became susceptible to infection with HIV-1. CD4 expression on monocytes cultured for 7 days was more than four times higher than that on freshly isolated cells, and the cultured cells were fully permissive to infection. These observations suggest that the differing susceptibility of monocytes and monocyte-derived macrophages to infection with HIV-1 is not simply proportional to the level of surface CD4 expression.

Rotavirus antigenicity is affected by the genetic context and glycosylation of VP7

Rotavirus variants resistant to neutralization were selected using monoclonal antibodies (N-MAbs) raised to VP7 of rotavirus G types 2, 3, and 6. Their neutralization resistance patterns and deduced VP7 amino acid sequences were obtained. Variants selected by two G2-specific N-MAbs from the homologous parent virus RV-5 showed single amino acid (aa) mutations in the antigenic A region. However, variants selected from reassortant virus RV-5 x SA11 (all genes from SA11 virus except that encoding VP7, which was from RV-5 virus) fell into two neutralization resistance groups. The first group showed identical mutations to the variants selected from RV-5 virus. The second group showed antigenic C region mutations, either alone or in combination with a mutation at aa 69. Variants selected from G3 parent viruses glycosylated at position 238 had a mutation at aa 96 in the A region, otherwise a C-region mutation at 211 was selected. Mutations at amino acid positions 94 or 96 were selected by monoclonal antibodies specific for each of the three serotypes. G3-specific monoclonal antibodies also selected mutations at position 148 and the new position of 264. This latter mutation resulted in substitution of aspartic acid for glycine and was located in a highly conserved and hydrophobic region of VP7. A G2-specific N-MAb selected variants with a mutation at aa 190 producing a new, utilized glycosylation site which we propose to be in new antigenic site E. The positions of mutations in antigenic variants and their antigenicity were determined by parental background genes and VP7 glycosylation.

Accumulation of unintegrated circular viral DNA in monocytes and growth-arrested T cells following infection with HIV-1

Cytocidal retrovirus infection is characterized by rapid accumulation of unintegrated viral DNA forms. These are thought to be generated by multiple rounds of reinfection and have been suggested to play a central role in cytopathogenesis. Here we have reviewed the work done in this area with HIV-1, mostly using acutely and chronically infected T cell and monocytic cell lines and in some cases T cells blocked at S phase of the cell cycle by aphidicolin treatment. To these studies, we have compared our findings with HIV-1 infected primary peripheral blood monocyte-derived macrophages and untreated and growth-arrested MT-2 cells, two biologically disparate cell populations. Using 1- and 2-long terminal repeat (LTR) circular forms as indicators of unintegrated viral DNA, we found similar rapid accumulation in both untreated and growth-arrested MT-2 cells. In contrast, we found much lower levels in monocyte/macrophages. Our findings suggest that accumulation of unintegrated viral DNA does not require virus production and reinfection in growth-arrested T cells. The significantly lower levels found in monocyte/macrophages may reflect superinfection resistance, allowing the maintenance of a persistent infection.

HIV-1 infection of monocyte-derived macrophages reduces Fc and complement receptor expression

Fc receptor (FcR) and complement receptor (CR) expression on HIV-infected monocyte-derived macrophages may be an important determinant of immune function. We studied the effects of HIV-1 infection of macrophages in vitro on FcR and CR expression. Macrophages were infected with HIV-1DV 7 days following isolation, and the expression of Fc gamma RI-III and CR3 were measured at intervals thereafter by flow cytometry. We found a reduction in receptor expression with the percentage of cells expressing FcRI 14 days post infection declining from 77% to 13%, FcRII fell from 96% to 85%, FcRIII from 45% to 9%, and CR3 from 91% to 67% 14 days following infection. As these receptors are important for macrophage function, their down-modulation may contribute to the pathogenesis of HIV-related disease.

Antibodies to gp41 and nef in otherwise HIV-negative homosexual man with Kaposi's sarcoma

A homosexual man with histologically confirmed Kaposi's sarcoma remained seronegative for HIV-1, HIV-2, and HTLV-1 on conventional tests over a 4-year period. HIV cultures were also negative on thirteen separate occasions. However, serum antibodies to synthetic peptide analogues of the gp41 and nef regions of HIV-1 were consistently detected on an enzyme immunoassay. Tests with the polymerase chain reaction with primers directed to the gag and env regions were negative. The antigens to which the antibodies were produced might have come from a defective HIV mutant, another retrovirus, or a hitherto unknown "agent of Kaposi's sarcoma" with similar antigenic epitopes.

Direct quantification of HIV-1 infectivity for monocyte--macrophages using an infectious focus assay

Monocyte--macrophages are important target cells and reservoirs for HIV. The existing methods for the quantification of infectious virus in HIV stocks are not totally satisfactory for use with macrophage cultures. We have developed an infectious focus assay for the direct quantification of virions infectious for human peripheral blood monocyte-derived macrophages adhering to plastic microtitre plates. The combination of an HIV-1 p24-antigen-specific monoclonal antibody and a beta-galactosidase-linked second antibody resulted in a sensitive and very specific assay. With 5-bromo-4-chloro-3-indolyl-beta-D-galactopyranoside as substrate, the assay proved to be as sensitive as p24 antigen quantification in culture supernatants.

Antigens of infectious laryngotracheitis herpesvirus defined by monoclonal antibodies

Monoclonal antibodies to glycoprotein and protein antigens of infectious laryngotracheitis virus (ILTV) were divided into five groups on the basis of their reactivity in immunofluorescence and Western blotting. Group I antibodies recognised a single band of 60 K and Group II antibodies recognised bands of 205, 160, 115, 90 and 85 k in Western blotting. In immunofluorescence both these groups of antibodies reacted with antigens located in the cytoplasm of fixed virus-infected cells and they also reacted with unfixed cells, suggesting that these antigens are on the surface of virus-infected cells. While Group I monoclonal antibodies did not react with extracts of tunicamycin-treated cells, some Group II antibodies recognised bands of decreased molecular weight compared to those present in untreated cells. The reactivity of the Group II antibodies with extracts of tunicamycin-treated cells suggested that they recognised at least three different epitopes which was confirmed by ELISA additivity assays. Monoclonal antibodies of Group III, Group IV and Group V recognised several low molecular weight proteins from 45 to 24 k. Immunofluorescence studies showed that these were nuclear and cytoplasmic antigens that were not present on the surface of virus-infected cells.

Immunogenic glycoproteins of infectious laryngotracheitis herpesvirus

The viral glycoproteins produced in cells infected with either vaccine strain or virulent isolates of infectious laryngotracheitis virus, an avian herpesvirus, were identified by in vitro labeling using [14C]glucosamine and [14C]mannose. Chicken antisera to the vaccine strain and to a virulent isolate, and rabbit antisera to the vaccine strain, immunoprecipitated four major viral glycoproteins of 205, 115, 90, and 60K mol wt. Additional glycoprotein bands were recognized by immune chicken and rabbit sera in Western blotting using a glycoprotein fraction purified from extracts of virus-infected cells. Monoclonal antibodies to the immunogenic glycoproteins were produced and characterized by immunoprecipitation and Western blotting. One group of monoclonal antibodies reacted only with the 60K glycoprotein, by both techniques, while a second group reacted with the 205, 115, and 90K glycoproteins in immunoprecipitation and with additional bands of 85 and 160K in Western blotting.

Intracellular localization of rotaviral proteins

The differential distribution of two SA 11 rotaviral capsid antigens in thin sections of infected cells was examined using antibody-coated colloidal gold electron-dense particles as specific post-embedding immunocyto-chemical labels. The treatment of thin sections of conventionally fixed and embedded tissue specimens with sodium metaperiodate allowed specific localization of the antigens in tunicamycin-treated, infected CV-1 cells. Both protein antigens were investigated with specific anti-rotavirus hyper-immune sera and with specific monoclonal antibodies. These studies showed that the major outer capsid glycoprotein, gp34, of SA11 rotavirus particles was mainly located within the cisternae and along the membranes of the rough endoplasmic reticulum. The antigen of the major inner capsid protein, p42, was identified attached to enveloped virus particles, and even more obviously, on laminar crystalline structures in the nucleus and cytoplasm of the infected cells.

The major surface glycoprotein of simian rotavirus (SA11) contains distinct epitopes

The polypeptide specificities on monoclonal antibodies previously derived against the SA11 simian, NIC bovine, and Wa human strains of rotavirus were determined by radioimmunoprecipitation of infected cell lysates. All the monoclonal antibodies derived using NIC and Wa were found to be directed against the major component of the inner capsid, while most of the SA11 monoclones were directed against the major outer capsid glycoprotein. When several SA11 glycoprotein-specific monoclonal antibodies were used in competitive binding studies, four distinct epitopes, which correlated with the functional activities of the antibodies, were defined. One epitope appeared most critical for virus neutralization, another was involved to a lesser extent, and the remaining two epitopes seemed to have no role. A possible topographical arrangement of these epitopes is suggested.

Derivation of neutralizing monoclonal antibodies against rotavirus

Monoclonal antibodies were derived against the SA11 simian, NIC bovine, and Wa human rotavirus strains and characterized by enzyme-linked immunosorbent assay, plaque neutralization, and hemagglutination inhibition. Several strain SA11-specific antibodies were found to have neutralizing and hemagglutination-inhibiting capacity.

Preparation and characterization of antisera to electrophoretically purified SA11 virus polypeptides

Antisera to SA11 virus proteins were prepared by immunizing rabbits with individual polypeptides separated by polyacrylamide gel electrophoresis under reducing or nonreducing conditions; the resulting antisera were characterized by four immunological methods. Results of complement fixation tests with double-shelled rotavirus particles and sera raised against reduced or unreduced proteins of the outer shell of the virus suggested the presence of common antigenic determinants in the outer capsid layers of SA11 and the Northern Ireland strain of calf rotavirus. In this test, antisera to outer shell polypeptides gp34 (O2) and gp25 (O4) cross-reacted with calf rotavirions, whereas those to p62 (O1) and p26 (O3) reacted only with the homologous virus. Antisera to the reduced outer shell proteins of the virus did not neutralize viral infectivity, nor did they possess hemagglutination inhibition activity. Evidence suggesting the presence of type-specific antigenic determinant(s) in the major inner protein p42 (I4) of SA11 virus, capable of inducing neutralizing antibody, is presented and discussed. Antisera produced against unreduced gp34 and p26 polypeptides of the virus contained type-specific neutralizing antibodies. Polypeptide gp34 was also capable of inducing hemagglutination inhibiting antibody. All of the antisera to unreduced polypeptides had agglutinating activity against double-shelled particles of homologous and heterologous rotaviruses.

Coproantibody response to rotavirus infection

During three months after a family outbreak of diarrhoeal disease, rotavirus-specific immunoglobulins of the IgA, IgG and IgM classes were measured by enzyme-linked immunosorbent assay in faecal extracts from the four people involved. Shortly afterwards, sequential extracts were obtained from another infant after a proven rotavirus infection. Rotavirus infection was diagnosed by electron microscopy in three of the patients from whom acute-phase faecal samples were obtained, and all five patients developed a transient specific-antibody response. Antirotaviral IgA, IgM and IgG all reached peak titres between two and four weeks after infection, then dropped back to undetectable levels after two months. If these findings are confirmed in larger numbers of cases, they will provide the basis for simple diagnosis of recent rotavirus infections, without the need of even a single sample of serum.

Measurement of immunoglobulin A, G, and M class rotavirus antibodies in serum and mucosal secretions

A solid-phase, enzyme-linked immunospecific assay for measurement of different immunoglobulin classes of human rotavirus antibodies is described. The antigen, which was adsorbed directly to polyvinyl microtiter plates, consisted of a clarified cell culture stock of the simian rotavirus SA 11. The assay was sensitive and reproducible and could readily be calibrated to determine concentrations of each class of antibody. The assay was applied to measurements of rotavirus antibodies in serum, colostrum, milk, and fecal samples. It particularly facilitates investigations of the role of immunoglobulin A antibodies in immunity to rotavirus infections.