Immunofluorescence assay reactivity patterns of serum samples presenting indeterminate Western blot results for antibodies to HIV-1 and HTLV-I/II in Cordoba, Argentina

A New Flow Cytometry-Based Single Platform for Universal and Differential Serodiagnosis of HTLV-1/2 Infection

In the present work, we developed and evaluated the performance of a new flow cytometry-based single platform, referred to as “FC-Duplex IgG1 (HTLV-1/2)”, for universal and differential serodiagnosis of HTLV-1/2 infection. The proposed technology employs a system for detection of IgG1 antibodies in a single competitive immunofluorescence platform by flow cytometry using fluorescently labeled MT-2/MoT cell line mix coupled to a highly sensitive development system (Biotin/Streptavidin/Phycoerythrin). The stability of fluorescent labeling and the antigenicity of MT-2 and MoT cell lines were confirmed upon storage at −20°C for 2, 6, and 12 months. The anti-HTLV-1/2 IgG1 reactivity, expressed as percentage of positive fluorescent cells (PPFC), was evaluated for each target antigen along the titration curve of test serum samples (1:32 to 1:4,096). Upon selection of target cell line and serum dilutions with higher segregation score between groups, the performance of “FIX” and “FIX & PERM” protocols was evaluated. The “FIX” protocol presented excellent performance indices (Se = 92%/Sp = 94%/AUC = 0.96; Se = 96%/Sp = 100%/AUC = 0.99) for the universal (HTLV-1/2 vs. NI) and differential (HTLV-1 vs. HTLV-2) diagnosis of HTLV-1 infection, respectively. Optimization of the “FIX” protocol using the principle of synchronous and asynchronous pairwise analysis further improved the performance of “FC-Duplex IgG1 (HTLV-1/2)”, using the “FIX” protocol for differential diagnosis of HTLV-1 and HTLV-2 infections (Se = 100%/Sp = 100%/AUC = 1.00). In conclusion, the “FC-Duplex IgG1 (HTLV-1/2)” method represents an innovation in the biotechnology segment with the potential to compose a serological kit for differential diagnosis of HTLV-1/2 infection for reference laboratories and blood centers.

The Impact of Sodium Dodecyl Sulfate and 2-Mercaptoethanol on Antibody and Antigen Binding

OBJECTIVE

To evaluate the effect of sodium dodecyl sulfate (SDS) and 2-mercaptoethanol (2-ME) on antigen-antibody binding when incubated at 100°C, which is the pretreatment temperature required for western blots.

METHODS

Serum that tested positive for hepatitis B surface antigen (HBsAg) plus loading buffer were mixed at a ratio of 4:1 and incubated in a water bath. We then detected HBsAg using double immunodiffusion and ELISA.

RESULTS

The HBsAg titer was 1:512 in the control group when incubated at 37°C. Incubation with SDS at 100°C reduced the antigen titer to 1:32. The inhibitory effect on HBsAg titer reached 96.9% after incubation at 100°C with SDS and 2-ME.

CONCLUSION

We detected strong inhibition of antigens in western blots via SDS and 2-ME. It is likely that false-negative results will be obtained from western blots of antigens with weak resistance to these reagents.

Human T-Lymphotropic virus type 1 infection in absence of tax gene: A challenge for molecular diagnosis

This is the first report of HTLV-1 infection without detectable tax gene. Even though the tax gene of HTLV-1 presents high genetic stability, in the case presented here no sequence of tax was detected by three different and widely used molecular assays targeting several sequences of the gene. Nevertheless, HTLV-1 pol and env genes and LTR region were properly detectable. Several PCRs targeting tax sequences have been developed and largely used for molecular diagnosis of HTLV infection since the tax gene of HTLV-1 is known to be well preserved and intolerant to changes or mutations. In the case reported here, molecular detection of the virus was challenging. HTLV prevalence is complex and in many regions remains unknown. The identification of HTLV-infected individuals is important to determine its actual prevalence and design strategies to reduce viral spread. The finding and communication of HTLV-1 defective-provirus strains is important and necessary to guide the selection of representative target sequences on HTLV genome to design molecular assays, highlighting that different sequences should be combined to ensure adequate diagnosis. The latter is especially relevant in cases when discordant results between serological and molecular assays. This report contributes to the knowledge of the overall molecular epidemiology of HTLV-1 and encourages the need of surveillance of HTLV-1 "missed tax gene profiles" and the evaluation of the impact of these defective viral variants on molecular diagnosis and human health.

[Serological diagnosis of HTLV-1/2: combination of screening assays to define the serological status in blood donors]

Alternative algorithms were evaluated in order to reduce the number of false reactive results for antibodies against HTLV-1/2. From 20,210 samples tested, 0.37% (74/20,210) was reactive by ELISA Murex. Of these, 23 were confirmed as positive by the indirect immunofluorescence assay whereas 51 were negative, being the positive predictive value (PPV) 31.08%. From a combination of the ELISA Murex assay with the particle agglutination assay (PA) and ELISA MP, the following results were obtained: 26/74 were reactive by ELISA Murex and PA, PPV 88.5% and 32/74 were reactive by ELISA Murex and ELISA MP, PPV 71.8 %. The ROC curve analysis determined that for an RP 4.74, the values for sensitivity, specificity, PPV and NPV by ELISA Murex were 100%, 98.04%, 95.8% and 100%, respectively. We propose that reactive samples by ELISA Murex with an RP d 4.74 should be retested in duplicate by PA, and the resulting concordantly nonreactive samples should be defined as negative for HTLV-1/2.

Field evaluation of the Abbott ARCHITECT HIV Ag/Ab Combo immunoassay

BACKGROUND

Fourth generation assays for HIV diagnosis are progressively being introduced into routine services, due to their improvement of diagnosis. In spite of this, HIV diagnosis remains a challenge in sub-Saharan Africa, due to false positive reactivity. There is a continuous need for field evaluations and routine validations of fourth generation HIV tests in African populations.

OBJECTIVES

Evaluate the performances of the ARCHITECT HIV Ag/Ab kit (Abbott) in a population living in an African setting-Cameroon compared to a population living in a European setting-France.

STUDY DESIGN

645 HIV samples from both France and Cameroon were evaluated. The positive panel (378 samples) included a diverse series of HIV-1 variants (groups M, N, O, and P) as well as HIV-2 samples. Results were compared to original diagnosis done with other 4th generation assays (AxSYM HIV Ag/Ab (Abbott) and Vidas HIV DUO QUICK) (bioMérieux).

RESULTS

Sensitivity of the ARCHITECT was 100% in both sites. It diagnosed all variants of the panel with different reactivity profiles following strain diversity. A wider range of reactivity was observed for group O. Specificity was slightly lower (97.6%) in Cameroon than in France (98.6%), probably due to a higher rate of false positive reactivity. ARCHITECT HIV Ag/Ab assay had high performances in clinical sensitivity and specificity and is adapted to the wide genetic diversity of viruses circulating in West Central Africa.

CONCLUSION

Our results further highlight the need to evaluate HIV diagnostic tests before introduction into routine diagnostic services both in the North and in the South.

Development and validation of a real-time PCR assay for a novel HTLV-1 tax sequence detection and proviral load quantitation

A quantitative real-time PCR (qPCR) assay using SYBR Green dye was established in order to detect and quantify the proviral DNA of HTLV-1 in peripheral blood mononuclear cells (PBMCs). Primers were designed, and the assay was standardized to amplify a novel, conserved HTLV-1 tax region. Proviral load was normalized to the amount of cellular DNA by quantitation of the human albumin gene. Firstly, the qPCR was assessed determining the specificity, sensitivity, dynamic range and intra- and inter-assay reproducibility of the technique. The limit of detection as determined by PROBIT analysis using dilutions of the standard was 2.97 copies. The assay had an excellent dynamic range from 10⁵ to 10¹ copies per reaction and good intra- and inter-assay reproducibility, CVs less than 2%. Secondly, the performance of the qPCR was tested on 40 HTLV-1 seropositive individuals. Proviral load for HTLV-1 carriers ranged from 2.2×10² to more than 8.3×10⁴ copies/10⁶ PBMCs. The high sensitivity and wide dynamic range allowed the determination of a broad range of HTLV-1 proviral loads in infected individuals. This assay is a valuable alternative diagnostic tool when current available serological assays are insufficient. In addition, it will facilitate the study of the relationship between proviral load and pathogenesis.

Can we improve the management of blood donors with nonspecific reactivity in viral screening and confirmatory assays?

Donors with nonspecific reactivity in viral screening or confirmatory assays are problematic for blood services because of donor management issues and product loss. Considerable experience has now accumulated in the use of screening and confirmatory assays; therefore, it is timely to examine the ways in which donors with nonspecific reactivity are managed. In this review, we summarize the causes and characteristics of nonspecific reactivity in blood donors and approaches for reducing the number of nonspecific reactive results and we offer some suggestions for improving the management of these donors.

Usefulness of a Nested-polymerase chain reaction for molecular diagnosis of human T-cell lymphotropic virus type I/II

This study aimed at implementing a Nested-polymerase chain reaction (Nested-PCR) for the molecular diagnosis of human T-cell lymphotropic virus type I/II (HTLV-I and HTLV-II) infections in peripheral blood mononuclear cells of infected subjects in Argentina. The sensitivity and specificity of the assay for the detection of regional strains were assessed by comparing them with the molecular assay of reference PCR-hybridization. The Nested-PCR detected 1 MT-2 cell (> or = 8 proviral copies)/1x10(6) non-infected cells showing high sensitivity for provirus detection. While both molecular assays showed high specificity (100%) for HTLV-I and HTLV-II detection, the sensitivity values differed: 100% for Nested-PCR and 67% for PCR-hybridization assay. Moreover, this technique showed less sensitivity for the detection of DNA sequences of HTLV-II (33%) than for the detection of DNA sequences of HTLV-I (75%). The high sensitivity and specificity of the Nested-PCR for regional strains and its low costs indicate that this assay could replace the PCR-hybridization assay for the molecular diagnosis of HTLV-I/II infections. It will be interesting to assess the usefulness of this assay as a tool for the molecular diagnosis of HTLV-I/II infections in other developing countries. Other studies that include a greater number of samples should be conducted.

Seroepidemiology of HTLV-I/II in Argentina: an overview

In this report, the results of seroepidemiologic studies of human T-lymphotropic virus type I (HTLV-I) and type II (HTLV-II) infections in different population groups in Argentina have been compiled. The studies have shown a high prevalence of HTLV-I/II infection in blood donors in the provinces in the north of Argentina (1.0% in Jujuy, 0.7% in Salta, and 0.6% in Formosa) and a low prevalence in the provinces in the central region of the country (<or=0.1%). High rates of HTLV-I (0.45%-2.78%) and HTLV-II (2.78%-21.9%) infections have been documented in Native Indian groups and have highlighted the importance of sexual and mother-to-child transmission of the viruses. The presence of HTLV-I/II antibodies in HIV-infected individuals indicates that both viruses are circulating in certain high-risk population groups. HTLV-I/II was detected in intravenous drug users (2.56%-21.7%), homosexual men (0.5-1.33%), prostitutes (0.8%), and hemophiliacs (2.8%). In conclusion, HTLV-I/II infection is circulating in low- and high-risk populations in Argentina, and these findings would support the view that selective screening for HTLV-I/II should be implemented to reduce the spread of infection.