A rapid and sensitive method of identification of HTLV-II subtypes

Sensitivity and specificity of a DNA polymerase chain reaction nonisotopic-based detection method for the confirmation of infection with human T-lymphotropic virus types I and II

BACKGROUND

A convenient, standard format for the detection of polymerase chain reaction (PCR) amplicons would increase the use of PCR for the confirmation of infection with human T-lymphotropic virus types I and II (HTLV-I and HTLV-II).

OBJECTIVES

To determine the sensitivity and specificity of an enzyme oligonucleotide assay (EOA) for the confirmation of infection with HTLV-I or HTLV-II.

STUDY DESIGN

The sensitivity of the EOA was determined by examining 88 specimens representing diverse geographic-associated genotypes and clinical manifestations. The specificity was determined by testing 40 HTLV-seroindeterminate (PCR-negative) specimens.

RESULTS

Of the 52 HTLV-I-positive specimens tested, 46 (88%) were confirmed positive for HTLV-I by the EOA; these included 25 of 30 (83%) specimens from asymptomatic carriers, 14 of 15 (93%) specimens from patients with HTLV-I-associated myelopathy, and all 7 specimens from patients with adult T-cell leukemia. Similarly, 33 of 36 (92%) HTLV-II-positive specimens were confirmed positive for HTLV-II. None of the specimens were wrongly classified. All specimens tested with distinct geographic-associated genotypes for HTLV-I and -II were detected by EOA. Analysis of seroindeterminate specimens, all of which were previously shown to be negative by nested PCR, showed that none of 40 were detected by either the HTLV-I or HTLV-II EOA.

CONCLUSIONS

The overall sensitivity of the EOA detection for confirmation of HTLV-I and HTLV-II was 79 of 88 (90%) and the overall specificity was 100%. These findings demonstrate that the EOA provides a simple, standardized assay system for reliable confirmation and typing of HTLV infection.

Comparative performances of an HTLV-I/II EIA and other serologic and PCR assays on samples from persons at risk for HTLV-II infection

BACKGROUND

HTLV-I and HTLV-II are related exogenous pathogenic human retroviruses. Until recently, ELISAs based on HTLV-I antigens have been used to screen for the presence of HTLV-I or -II antibodies. The HTLV-I-based assays have not been as sensitive in detecting antibodies to HTLV-II as in detecting antibodies to HTLV-I. The Abbott HTLV-I/HTLV-II ELISA uses a combination of HTLV-I and HTLV-II antigens to detect antibodies to the whole HTLV group. The performance of this ELISA was compared to that of several HTLV-I-based serologic assays and an HTLV-II PCR assay in cohorts of South American Indians and New York City IV drug users (IVDUs) in whom HTLV-II is endemic.

STUDY DESIGN AND METHODS

Sera from 429 South American Indians and New York City IVDUs were evaluated for HTLV antibodies by the use of three ELISAs (rgp21-enhanced HTLV-I/II, Cambridge Biotech; Vironostika HTLV-I/II, Organon Teknika; and HTLV-I/HTLV-II, Abbott), and a Western blot (WB) assay. Peripheral blood leukocyte DNA from each person was analyzed for HTLV-I and HTLV-II pol DNA via PCR. The HTLV-II PCR-positive samples were further subtyped via cloning and sequencing and/or oligomer restriction.

RESULTS

Two hundred four samples (48%) were positive for HTLV-II by serologic and/or PCR assays. All of the positive samples from the Indians and approximately one-third of the positive samples from the IVDUs were of the HTLV-IIB subtype. Comparative analyses indicate that the sensitivity and specificity of the various assays were: PCR, 98 and 100 percent; Abbott HTLV-I/HTLV-II, 78 and 95 percent; Cambridge Biotech HTLV-I/II, 76 and 96 percent; Vironostika HTLV-I/II, 71 and 98 percent; and WB, 73 and 100 percent, respectively.

CONCLUSION

There were no significant differences among the sensitivities and specificities of the HTLV-I/II ELISAs (p values, 0.056-0.438). The WB and PCR assays were much more specific than the other serologic assays (p</=0.03). However, the PCR assay is significantly (p<0.001) more sensitive than any of the serologic assays in the detection of HTLV-II infection. Thus, optimal detection of HTLV-II infection would seem to require both serologic and DNA PCR assays.

Endemic infection with HTLV-IIB in Venezuelan Indians: molecular characterization

The peripheral blood of 41 Yaruro and Guahibo Indians from Venezuela was examined for HTLV antibodies and DNA. Twenty-five samples (61%) were found to be infected with HTLV-IIB. The sensitivities of the serologic and DNA polymerase chain reaction (PCR) analyses were 80% and 96%, respectively. Epidemiologic studies supported both sexual and perinatal transmission of the virus. Sequence analyses of the HTLV-IIB strains from these Indians indicate that they are unique relative to HTLV-II detected in other groups of humans. HTLV-IIB-G2 isolated from a Guahibo Indian is the most divergent HTLV-IIB strain relative to the prototype HTLV-II NRA.

High prevalence of false-negative anti-HTLV type I/II enzyme-linked immunosorbent assay results in HIV type 1-positive patients

A high frequency of false-negative anti-HTLV-I/II ELISA results has been reported by several authors. To verify the possible underestimate of the prevalence of HTLV-II infection in subjects infected by HIV-1, we used the PCR to investigate the presence of HTLV DNA in peripheral blood mononuclear cells (PBMCs) collected from a group of 67 HIV-1-positive anti-HTLV-I/II ELISA-negative individuals; the study population included 31 patients with HIV-1-related peripheral neuropathy (PN), 15 with non-Hodgkin lymphoma (NHL), and 23 without PN or NHL. Two subjects had both PN and NHL. All of the patients who were positive at PCR were investigated for the presence of serum anti-HTLV-I/II antibodies by means of Western blot (WB). Eighteen (26.9%) of the 67 anti-HTLV-I/II ELISA-negative patients had HTLV DNA in their PBMCs and WB-detectable serum antibodies directed against one or more HTLV antigens. The individuals affected by predominantly sensory polyneuropathy (PSP) had a significantly higher prevalence of HTLV DNA than the others. All of the patients in whom HTLV-I/HTLV-II discrimination was successful had HTLV-II, with the exception of one patient who was infected by HTLV-I. The present study confirms the possibility of HTLV infection in the absence of ELISA-detectable serum anti-HTLV-I/II antibodies, especially in the particular setting of HIV-1-infected individuals. Moreover, the fact that the prevalence of HTLV DNA was significantly higher in the subjects affected by predominantly sensory polyneuropathy further supports the possibility of an association between HIV-1-related PSP and HTLV-II.

Dissimilar evolution of B-locus versus A-locus and class II loci of the HLA region in South American Indian tribes

Native American populations have a limited HLA polymorphism compared with other ethnic groups. In spite of this, many novel HLA-B locus alleles, not observed in other populations, have been identified in South American tribes, and rapid evolution of this locus has been suggested. We have studied unrelated subjects of the Toba (TOB n = 116), Wichi (WIC n = 46) and Pilaga (PIL n = 14) tribes from northeastern Argentina to investigate the extent of the HLA polymorphism and obtain clues of selective forces that may have acted in these populations. In these tribes the number of HLA alleles is small at all loci except HLA-B, which presents 22 alleles. Seven novel alleles were characterized including 5 of HLA-B (B*35092, B*3518, B*3519, B*4009, B*4803) 1 at HLA-A (A*0219) and 1 at DRB1 (DRB1*0417). All these variants may have arisen by gene conversion events. Some of the novel variants represent the most frequent alleles of these populations (B*4803 in TOB and PIL; B*3519 in WIC) or are the most frequent subtypes in their lineages. HLA-A, B, DRB1,DQA1 and DQB1, but not DPB1, display relatively similar gene frequencies. This results in high heterozygosity in all the tribes for all the loci studied except HLA-DPB1. The larger polymorphism and the generation and maintenance of novel alleles at the HLA-B locus suggests a more specialized response of this locus to evolutionary forces. These effects may be related to the nature of the polymorphism, to the number of founder alleles and to the functional characteristics of the individual alleles.

Highly endemic human T-lymphotropic virus type II (HTLV-II) infection in a Venezuelan Guahibo Amerindian group

Sera from 166 Guahibo Indians (55% of the population) living in southwest Venezuela were screened by enzyme-linked immunoassay for antibodies to human T-cell lymphotropic virus (HTLV) I and II. Positive samples were confirmed by immunofluorescence and Western blot. Forty-one Guahibos (24.8%) were found to be seropositive. Polymerase chain reaction (PCR) analysis of proviral DNA in mononuclear cell lysates revealed the virus to be HTLV-II. Prevalence increased with age, and sexual contact with HTLV-II-seropositive partners was identified as a risk factor for infection. PCR amplification of a region of the pol gene, utilizing the primer pair SK110/SK111, with subsequent digestion of the 140-base-pair amplification products with HinfI and MseI restriction enzymes, showed an HTLV-II subtype-b restriction pattern in all cases. These data suggest that the substrain infecting this Guahibo community belongs to the b subtype, the most frequent among Paleo-Amerindian populations.

HTLV infection in ELISA-negative blood donors

Human T lymphotropic viruses (HTLVs) have a limited spread in the general populations of Western countries. Consequently, the transfusional risk for HTLV is consider to be low in Italy and the screening for anti-HTLV-I/II antibodies has not yet been introduced. In 1992, 1087 blood donors attending a transfusional center in northern Italy underwent anti-HTLV-I/II screening carried out by means of two different ELISA tests. Eleven individuals who were negative at the first test were borderline at the second, eight of them showing reactivity to Western blot (WB). Polymerase chain reaction (PCR) for the detection of HTLV DNA, subsequently performed on the peripheral blood mononuclear cells of these 11 subjects, was positive in the same 8 WB-reactive donors. Five of them were infected by HTLV-II, and three by HTLV-1. Our results confirm that the sensitivity of the ELISA tests actually used for the detection of HTLV-I/II antibodies is low, and that HTLV-infected blood donors may be frequently undetected. Moreover, in our study population, the prevalence of HTLV infection (0.73%) was greater than that which might be expected from the existing seroepidemiological data in Italy.

Molecular subtyping of human T-cell lymphotropic virus type 2 by single-strand conformation polymorphism analysis. Retrovirus Epidemiology Donor Study Group

Molecular subtyping of human T-cell lymphotropic virus type 2 (HTLV-2) by the currently used method of restriction fragment length polymorphism analysis may not be sufficiently discriminatory for transmission studies because of the predominance of single restriction types in various HTLV-2-infected populations. The utility of single-strand conformations polymorphism (SSCP) analysis was evaluated as a tool to improve the sensitivity of the subtyping of HTLV-2. The assay was designed to target a highly variable region in the long terminal repeat and was shown to be able to detect single nucleotide changes in cloned HTLV-2 sequences. Analysis of 52 HTLV-2 samples, of which 32 were from 16 sex partner pairs (16 males, 16 females), showed nine different SSCP patterns. Identical SSCP results were obtained for each of the 16 couples, suggesting the presence of similar viral genotypes and, therefore, supporting the likelihood of sexual transmission of HTLV-2 in each of these couples. Furthermore, SSCP analysis of seven HTLV-2 samples of the same restriction type (b5) showed five different SSCP patterns. Nucleotide sequencing of two samples with distinct SSCP patterns confirmed the sequence differences. SSCP provides a facile and discriminatory tool for the differentiation of HTLV-2 strains, including those previously indistinguishable by restriction fragment length polymorphism.