Human T-lymphotropic virus type I seroprevalence among Japanese Americans.

The epidemiology of human T-lymphotropic virus type I (HTLV-I) infection is not well defined in Japanese Americans. This impairs using approaches that could reduce viral transmission and monitor carriers for the disease. Using enzyme-linked immunosorbent assay and p21e recombinant Western blot testing, HTLV-I antibody was measured in unlinked samples from Japanese-American patients at 4 physicians'' offices in San Francisco, California. Of 442 patients, 4 (0.9%; 95% confidence interval 0.25%, 2.3%) were confirmed seropositive, all with an HTLV-I rather than an HTLV-II pattern on Western blot. Seroprevalence was highest among the issei or immigrant generation (3/230 or 1.3%) compared with the second-generation nisei (1/191 or 0.5%) or third-generation sansei (0 of 17). Prevalence did not differ by age or sex, although the number of positive subjects in each subgroup was small. Of 88 patients with familial origins in endemic areas of southern Japan, none were seropositive. In this sample of Japanese Americans, HTLV-I seroprevalence was lower than in residents of endemic southern Japan but higher than among American blood donors. The prevalence was most similar to that in nonendemic areas of Japan. The public health implications of HTLV-I infection among Japanese Americans are discussed.     

Prevalence of antibodies to human T cell leukaemia/lymphoma virus in blood donors in north London.

OBJECTIVES--To determine the prevalence of antibodies to the human T cell leukaemia/lymphoma viruses (HTLV-I and HTLV-II) in blood donors in north London in order to assess the economic impact and the logistic effects that routine screening would have on the blood supply. DESIGN--All donations collected by the north London blood transfusion centre between January 1991 and June 1991 were screened for antibodies to HTLV-I and HTLV-II by modified, improved Fujirebio gel particle agglutination test. Positive samples were titrated and retested as necessary. SUBJECTS--96,720 unpaid volunteers, who gave 105,730 consecutive donations of blood and plasma. SETTING--North London blood transfusion centre. MAIN OUTCOME MEASURE--Observed numbers of donors confirmed to be seropositive for HTLV by reference laboratories. RESULTS--Of 2622 (2.5%) initially reactive samples, 414 (0.4% of all samples) gave a titre of > or = 1 in 16 on the modified agglutination test. Thirty five of the 414 serum samples yielded positive results on one of two enzyme linked immunosorbent assays (ELISA (Cambridge Biotech and Abbot)), and none of these results were confirmed by either reference laboratory. Five samples yielded positive results on both ELISAs and all five of these were confirmed to contain antibodies to HTLV. One of the five contained antibodies to HTLV-II and the others antibodies to HTLV-I. Four seropositive donors were white women whose only risk factor for infection was sexual contact. The fifth (positive for antibodies to HTLV-II) was an Anglo-Caribbean man who admitted to previous misuse of intravenous drugs. CONCLUSION--The prevalence of antibodies to HTLV in blood donors in north London was one in 19,344 (0.005%). Up to 100 donors a year might be identified in the United Kingdom as being infected with HTLV, although prevalence in different regions may vary considerably.     

Immunoglobulin subclasses of antibodies to human T-cell leukemia/lymphoma virus I-associated antigens in acquired immune deficiency syndrome and lymphadenopathy syndrome

Immunoglobulin G (IgG) and IgM antibodies to human T-cell leukemia/lymphoma virus-I (HTLV-I)-associated membrane antigens (HTLV-I-MA) were assayed by indirect cytospin immunofluorescence, and IgG and IgM antibodies to purified HTLV-I were assayed by enzyme-linked immunosorbent assay in sera from 119 immunologically well-characterized promiscuous male homosexuals in The Netherlands, of whom 9 suffered from acquired immune deficiency syndrome (AIDS), 18 suffered from lymphadenopathy syndrome (LAS), and 5 suffered from gay bowel syndrome. Antibodies to HTLV-I-MA were present in four of nine AIDS patients, including one patient with antibodies to purified HTLV-I. Antibodies to HTLV-I-MA were present in 6 of 18 LAS patients, including 3 patients with antibodies to purified HTLV-I. Of five patients with gay bowel syndrome, one had IgG and IgM antibodies to HTLV-I-MA. Of the four HTLV-I seropositive AIDS patients, two had IgG and IgM antibodies to HTLV-I or HTLV-I-MA, one had only IgG antibodies, and one had only IgM antibodies. Of the six HTLV-I seropositive LAS patients, four had IgG and IgM antibodies to HTLV-I or HTLV-I-MA, and two had only IgM antibodies. In the sera from 27 healthy homosexuals with and 60 without T-cell subset imbalances, no antibodies to HTLV-I or HTLV-I-MA were detected.     

Human T-lymphotropic virus type I (HTLV-I) and tropical spastic paraparesis or HTLV-I-associated myelopathy in Hawaii.

Tropical spastic paraparesis or human T-lymphotropic virus type I (HTLV-I)-associated myelopathy is a degenerative encephalomyelopathy with pyramidal tract dysfunction affecting the lower extremities. It is associated with HTLV-I infection and found primarily in the Caribbean region and in southwestern Japan. Five cases of tropical spastic paraparesis (or HTLV-I-associated myelopathy) in Hawaii are reported. All five patients were born in Hawaii; four are women. Each of the patients has parents who were from HTLV-I-endemic areas of Japan. Two of these patients had serum antibodies to HTLV-I. Five of six of the spouses and children of the seropositive patients were also seropositive. Viral cultures of lymphocytes from both seropositive patients and two of the three seropositive children were positive for HTLV-I. None of the five patients had a history of antecedent blood transfusion, multiple sexual partners, or intravenous drug use. There is no evidence of adult T-cell leukemia or lymphoma in any of the patients or their families. Given the increasing seroprevalence of HTLV-I in the United States, clinicians need to be alert to new cases of this disorder.     

Human T-cell lymphotropic virus type I infection and disease in the Pacific basin.

Human T-cell lymphotropic virus type I (HTLV-I), the cause of adult T-cell leukemia/lymphoma (ATLL) and HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP), is widespread in the Pacific basin. Modes of virus transmission include blood transfusion (and intravenous drug use), breast milk, and sexual intercourse. High prevalences of HTLV-I infection and disease occur among the inhabitants of southwestern Japan and among first- and second-generation (issei and nisei) Japanese-Americans in the Hawaiian Islands. Other Pacific populations with high prevalences of HTLV-I infection include several remote groups in West New Guinea, Papua New Guinea, the Solomon Islands, and Vanuatu, which have had no contact with Japanese or Africans. By contrast, Micronesian and Polynesian populations, even those with prolonged contact with Japanese, exhibit low prevalences or no evidence of HTLV-I infection. Low prevalences of infection are also found in Australia, except among some aboriginal populations. Changing patterns of HTLV-I infection and disease are no better exemplified than in Japan, where striking reductions in transfusion-acquired infection and subsequent development of HAM/TSP have followed the institution of nationwide screening of blood donors for HTLV-I infection. Furthermore, virus transmission from mother to infant by means of infected breast milk has been markedly curtailed in HTLV-I-hyperendemic regions in Japan by interrupting the practice of breast feeding by HTLV-I-infected mothers. The next frontier of HTLV-I research is in Melanesia, where highly divergent sequence variants of HTLV-I have been discovered.     

Mapping of immunogenic regions of human T cell leukemia virus type I (HTLV-I) gp46 and gp21 envelope glycoproteins with env-encoded synthetic peptides and a monoclonal antibody to gp46

Antigenic sites on human T cell leukemia virus type I (HTLV-I) gp46 and gp21 envelope glycoproteins that are immunogenic in man were studied with envelope gene (env)-encoded synthetic peptides and a mAb to HTLV-I gp46 envelope glycoprotein. Antibodies in 78% of sera from HTLV-I seropositive subjects reacted with synthetic peptide 4A (amino acids 190 to 209) from a central region of HTLV-I gp46. Human anti-HTLV-I antibodies also bound to synthetic peptides 6 (29% of sera) and 7 (18% of sera) from a C-terminal region of gp46 (amino acids 296 to 312) and an N-terminal region of gp21 (amino acids 374 to 392), respectively. mAb 1C11 raised to affinity-purified HTLV-I gp46 reacted with gp46 external envelope glycoprotein and gp63 envelope precursor in immunoblot assay and also bound to the surface of HTLV-I+ cells lines HUT-102 and MT-2. Antibody 1C11 did not react with HTLV-II or HIV-infected cells or with a broad panel of normal human tissues or cell lines. In competitive RIA, anti-gp46 antibody 1C11 was inhibited from binding to gp46 either by antibodies from HTLV-I seropositive subjects or by HTLV-I env-encoded synthetic peptide 4A, indicating that 1C11 bound to or near a site on gp46 within amino acids 190 to 209 also recognized by antibodies from HTLV-I-seropositive individuals. When tested in syncytium inhibition assay, mAb 1C11 did not neutralize the infectivity of HTLV-I. Thus, HTLV-I infection in man is associated with a major antibody response to a region of gp46 within amino acids 190 to 209 that is on the surface of virus-infected cells.     

Patterns of reactivity of Epstein-Barr virus-specific T cells in A-type donor cultures after reactivation with autologous A- or B-type transformants.

Regression endpoints were assessed in cultures from 11 Epstein-Barr (EB) virus A-type seropositive donors and 2 seronegative donors using A- and B-type EB virus preparations. In 9/11 of the seropositive donors, the resulting endpoints using A-type or B-type virus were similar and demonstrated a significant T cell response to both virus types. However, the regression endpoints for 2/11 seropositive donors were reproducibly higher with B-type virus compared with A-type virus, indicating a weak T cell response to the B-type virus compared with that to the A-type virus. Seronegative donor cultures showed no regression. The patterns of reactivity of bulk cultures of EB virus-specific cytotoxic T cells and T cell clones from selected seropositive donors were compared. Four of six donors showed evidence of a cytotoxic T cell response to A- and B-type autologous transformants while cytotoxic T cells from 2/6 donors (corresponding to those identified as lacking regression to B-type virus) lysed autologous targets infected with A-type but not B-type virus. The results show that while most A-type seropositive donors are capable of mounting a T cell response to A- and B-type virus, certain donors apparently lack B-type reactivity.     

A field study of infection with human T-cell leukemia virus among African primates

African non-human primates were surveyed seroepidemiologically for natural infection of human T-cell leukemia virus type I (ATLV/HTLV-I) or its closely related virus(es). Materials from three genera (Cercopithecus, Papio, and Theropithecus), four species (grivet monkey, Anubis baboon, Hamadryas baboon, and gelada), totalling 983 animals under natural conditions, were obtained in a field study in Ethiopia. Virus infection was determined by the indirect immunofluorescence test using HTLV-I specific antigens. Animals seropositive for HTLV-I were found among grivet monkeys and Anubis baboons including the hybrid offspring between Anubis and Hamadryas baboons but not pure-Hamadryas baboons and geladas. From these results, the HTLV-I family was proved to be widespread on the African continent and was regarded as a common retrovirus among catarrhines.     

Human T lymphotrophic virus type I may not be associated with multiple sclerosis in Japan.

To study the possible involvement of human T lymphotrophic virus type I (HTLV-I) or a related retrovirus in Japanese cases of multiple sclerosis (MS), we first performed a Western blot analysis with purified Ag of HTLV-I. Ten out of 31 MS patients (32.2%), 19 of 66 patients (28.8%) with other neurologic diseases, and 2 of 64 healthy blood donors (3.1%) had antibodies reactive with Ag corresponding to the group-specific Ag (gag) proteins (p15, p19, p24) on their sera. There were no significant differences between MS and other neurologic diseases concerning the patterns and the frequency. Second, we tried to establish T cell lines from PBMC of 22 MS patients with crude IL-2 without accessory cells, because HTLV-I-infected T cells can be immortalized in a high ratio under those conditions. Only one T cell line (MS-14C), however, could be maintained in long term culture. MS-14C and cultured T cells for 3 to 5 wk derived from MS patients were examined by Southern blot analysis under both stringent and low stringent conditions with HTLV-I as a probe. No HTLV-I related bands could be detected. By polymerase chain reaction examination, we also could not detect HTLV-I provirus genome in the fresh PBMC from 20 MS patients, although some of them had gag-reactive antibodies. Our data do not favor the hypothesis of HTLV-I or an HTLV-I-related human retrovirus in the etiology of MS.     

Isolation of a human T-lymphotropic virus type I strain from Australian aboriginals.

A human T-lymphotropic virus type I (HTLV-I) strain was isolated in a CD4+ T-lymphocyte culture established from a healthy seropositive Australian Aboriginal. This isolate, identified as HTLV-IMSHR-1, was detected by immunofluorescence with monoclonal antibodies, by the presence of gag-encoded protein p24 in the culture supernatant, and by cocultivation leading to infection and transformation of lymphocytes from an HTLV-I-negative donor. By using the polymerase chain reaction technique, the env gene and segments of the pol and pX regions of the proviral genome of HTLV-I(MSHR-1) were amplified and sequenced. Comparison with the envelope sequences of prototype strains revealed up to 7% divergence at the nucleotide level and 3.1 to 4.3% divergence in the predicted amino acid sequence. Phylogenetic analysis showed that the Australian and Melanesian isolates are related. Differential reactivity with monoclonal antibodies suggests that gag protein p19 of HTLV-I(MSHR-1) is also divergent. The potential for antigenic divergence between the prototype HTLV-I isolates and the Austro-Melanesian variants requires further investigation, because it would have implications for serodiagnosis and vaccine development.     

A serological survey of simian virus 40 in monkeys

A serological survey of simian virus 40 (SV 40) was conducted by an immune adherence hemagglutination (IAHA) test in breeding monkeys. Of a total of 356 monkeys tested, 168 (47.2%) were seropositive. All 168 seropositive monkeys were detected from 224 monkeys which were bred or kept in Japan for a long time. In contrast, none of the 132 monkeys which were newly imported from Southeast Asia was seropositive. If a comparison was made in the same breeding place, the positive rate of 80.4% (111/138) of Japanese monkeys was significantly (P less than 0.01) higher than the 59.5% (25/42) among rhesus monkeys. The positive rate and the IAHA titers were higher in older age group (greater than 5 years) but similar in male and female. These results indicated that SV 40 was highly prevalent among breeding monkeys in Japan.     

Molecular evolution and geographic origins of type 1 human lymphotrophic virus in Colombia detected by RFLP polymorphism

The human T-lymphotropic virus type I (HTLV-I) infection is a public health problem in many endemic areas of Colombia. The subtyping of HTLV-I was based on the analysis of restriction fragment length polymorphisms (RFLP) in 3'LTR proviral DNA. From 31 HTLV-I isolates collected throughout Colombia, a RFLP analysis in a 737 bp 3'LTR fragment was performed. Fifty-eight percent (18/31) were identified as the Cosmopolitan subtype a, 19.4% (6/31) in the West African subtype b, 12.9% (4/31) in the Cosmopolitan subtype b and 9.6% (3/31) in the West African subtype c. The phylogenetic analysis of 3'LTR nucleotide sequences indicated that all the isolates in the current study were in the subgroup B or Japanese, in contrast with the highly divergent isolates from native Amerindians grouped in subgroup a or Transcontinental. The supported hypothesis was that of a post-Columbus introduction of virus represented in the African-American communities of the Colombian South Pacific. Some viral isolates from Colombian native Amerindians exhibited a nucleotide variation compatible with a Paleolithic introduction of the virus. The genetic diversity of HTLV-I in Colombia is complex and probably represents several independent introductions of lymphotropic virus.     

Risk factors for human T cell lymphotropic virus type I among injecting drug users in northeast Brazil: possibly greater efficiency of male to female transmission

It was observed in the city of Salvador, State of Bahia, the highest seroprevalence of human T cell lymphotropic virus type 1 (HTLV-I) infection in Brazil as demonstrated by national wide blood bank surveys. In this paper, we report results of an investigation of drug use and sexual behavior associated with HTLV-I infection among male and female injecting drug users (IDUs) in Salvador. A cross sectional study was conducted in the Historical District of Salvador from 1994-1996 (Projeto Brasil-Salvador) and 216 asymptomatic IDUs were selected using the snowball contact technique. Blood samples were collected for serological assays. Sera were screened for human immunodeficiency virus (HIV-1/2) and HTLV-I/II antibodies by ELISA and confirmed by Western blot. The overall prevalence of HTLV-I/II was 35.2% (76/216). The seroprevalence of HTLV-I, HTLV-II and HIV-I was for males 22%, 11.3% and 44.1% and for females 46.2%, 10.3% and 74.4% respectively. HTLV-I was identified in 72.4% of HTLV positive IDUs. Variables which were significantly associated with HTLV-I infection among males included needle sharing practices, duration of injecting drug use, HIV-I seropositivity and syphilis. Among women, duration of injecting drug use and syphilis were strongly associated with HTLV-I infection. Multivariate analysis did not change the direction of these associations. Sexual intercourse might play a more important role in HTLV-I infection among women than in men.     

Seroepidemiology of viral infections among intravenous drug users in northern California.

Intravenous drug users are frequently exposed to parenterally transmitted viral infections, and these infections can spread to the general population through sexual activity. We investigated the prevalence of serologic markers for human immunodeficiency virus type 1 (HIV-1), human T-cell lymphotropic virus type I/II (HTLV-I/II), hepatitis B virus (HBV), and hepatitis C virus (HCV) in intravenous drug users and their sexual contacts. Of 585 drug users from northern California tested for these serologic markers, 72% were reactive for the antibody to HCV, 71% for the antibody to hepatitis B core antigen, 12% for HTLV-I/II antibodies, and 1% for the HIV-1 antibody. The prevalence of serologic markers for these four viruses correlated with the duration of intravenous drug use, the ethnic group, and the drug of choice. More than 85% of subjects infected with either HCV or HBV were coinfected with the other virus. All persons reactive to HTLV-I/II antibodies had antibodies for either HBV or HCV. Of 81 sexual contacts tested, 17% had evidence of HBV infection while only 6% were reactive for HTLV-I/II antibodies and 4% for the antibody to HCV. None of this group was infected with HIV-1. We conclude that HTLV-I/II and HCV are inefficiently transmitted to sexual contacts while HBV is spread more readily. Programs designed to discourage the sharing of drug paraphernalia, such as needle and syringe exchanges, should decrease the risk of parenterally spread viral infections in intravenous drug users and thus slow the spread of these infections to the general population.     

Sera from patients with multiple sclerosis react with human cell T lymphotropic virus-I gag proteins but not env proteins--Western blotting analysis

To study the possible involvement of human T cell lymphotropic virus type I (HTLV-I)-related agent in Japanese multiple sclerosis (MS), we performed a Western blotting analysis, using purified viral antigens, on sera from 46 patients with MS, nine patients with other neurologic diseases, and 11 healthy controls. Of 46 MS patients, 11 (24%) had antibodies reactive with antigens corresponding to the group-specific antigen (gag) proteins (p15, p19, and p24), although the prevalence was lower than that reported in a recent study using an enzyme-linked immunosorbent assay (ELISA). Despite the lower frequency of immunoreactivity, Western blotting technique had merits of identification of multiple antigens and higher specificity for detection of antibodies than ELISA. Those sero-positive patients consisted of four cases with IgG antibodies reactive mainly to the gag p24 and/or p15, four with IgM antibodies mainly to the gag p24 and/or p19, and three with both IgG and IgM antibodies. These immunostaining patterns of MS sera were clearly distinguishable from those of adult T cell leukemia patients who had antibodies to the envelope (env) proteins and its precursors in addition to the gag proteins. The antibody in MS sera was generally of low titer and reactive at a high serum concentration (1/10 dilution). None of the sera from patients with other neurologic diseases and healthy controls had the viral antibodies. These findings indicate that at least one quarter of Japanese MS patients have antibody responses to a hitherto unidentified agent related to HTLV-I, which possibly plays a part, primarily or secondarily, in the pathogenesis of those patients.     

Human retroviral env and gag polypeptides: serologic assays to measure infection

Humoral antiviral responses to human retrovirus infections identify persistently infected individuals and can be used to characterize virus-host interactions. Antibodies to native viral polypeptides have been reliably measured, although quantitation of env antibodies is difficult due to a lack of purified antigens. To quantitate antibodies to env antigens, bacterially expressed cloned env polypeptides from the transmembrane regions of human T lymphotropic virus types I and III were applied to nitrocellulose filters in an immunodot assay. A combination of the sensitivity of the Western blot procedure and the specificity of peptides from defined viral sequences was used to detect 49/49 HTLV-III/LAV-infected individuals previously defined as seropositive by radioimmunoprecipitation sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Of these HTLV-III/LAV envelope seropositive people, 22% lacked antibody to p24 in a radioimmunoassay. In contrast, the sensitivity of antibody detection to HTLV-I env antigens and p24 were comparable. Antibodies to HTLV-I and HTLV-III/LAV env transmembrane peptides were not cross-reactive. Levels of antibody to env antigens of both HTLV-I and HTLV-III/LAV persisted without change for at least 26 mo, suggesting that most infections represent stable virus-host interactions. The use of bacterially expressed env peptides offers a rapid serologic approach for distinguishing human retroviral infections and can be used to define immune responses to specific regions of the viral genome.     

No Proof of HTLV-I/II in Intravenous Drug Abusers with a High Rate of HIV-1 Infection in Central Thailand

Serum specimens of 1,074 intravenous drug abusers (IVDA) were examined for infection with HIV-1, HTLV-I and HTLV-II in central Thailand. Three hundred and sixty-two of the specimens were seropositive for HIV-1 (33.7%). The HIV-1 seropositive IVDAs exhibited increased seropositivity with age through group 40–44 and significantly decreased seropositivity over the age of 45. In contrast, no seropositivity to either HTLV-I or -II was detected in the samples tested by a particle-agglutination assay for HTLV followed by type-specific Western blotting for HTLV. Reference to previous reports suggested that the rate of HIV infection in IVDAs has decreased with no HTLV-I or HTLV-II in Thailand when compared with that of the HIV infection in 1992.     

Production,purification, and serologic application of a recombinant peptide from the carboxyl terminus of the χ gene protein of human T-cell lymphotropic virus type I

A fusion peptide containing 95 amino acid residues from the carboxyl terminus of the χ-Lor (χ) protein of human T-cell lymphotropic virus type I (HTLV-I) was produced in quantity in Escherichia coli and purified to >95% homogeneity by reverse-phase high-performance liquid chromatography with a yield of approximately 15 mg protein from 3.3 g wet cell paste of 1.5 liter induced cell culture. The purified recombinant peptide is immunogenic or selectively immunogenic in adult T-cell leukemia patients and individuals who are seropositive normals. Rabbit polyclonal antisera prepared against the purified χ gene fusion peptide react strongly and specifically against the peptide. This approach is highly suitable for scale-up production of abundant and pure HTLV-I reagents for subsequent application in serodiagnostic, functional, and structural approaches relating to the etiology of the virus.     

The expression of hepatitis-C virus antigen by immunohistochemical stain and polymerase chain reaction in corneas of seropositive corneal donors

Background: Of the donor corneas rejected for transplantation, the largest group is that from donors testing seropositive for hepatitis C virus (HCV). In situations of severe shortage in supply of donor corneal tissue, we may consider the use of seropositive donors for transplantation if we can prove with high certainty the absence of HCV RNA in the donor corneal tissue. Polymerase chain reaction (PCR) is a highly sensitive and specific technique for direct detection of HCV RNA and can be used for this purpose. Nevertheless, it is not applicable for routine clinical use in most eye departments due to its unavailability and cost effectiveness.Purpose: To study the possible use of immunohistochemical method for detection of HCV antigen in corneal tissue of seropositive donors and correlate the results with those of PCR. Immunohistochemical methods have not yet been studied in donor corneal tissue.Materials and methods: Eight corneas of 4 seropositive and 8 corneas of 4 seronegative corneal donors were studied by immunohistochemical and PCR methods for the presence of HCV antigen in their corneal tissue and sera.Results: HCV RNA was not detected in the sera and corneal tissue of all seropositive and seronegative corneal donors by either PCR and immunohistochemical methods.Conclusion: Although the study is too small for conclusive results, the correlation between the immunohistochemical and PCR studies for direct detection of HCV antigen in corneal tissue of seropositive donors may raise the possibility of using the immunohistochemical method for screening of donor corneas for the detection of HCV antigen. A larger prospective study investigating the sensitivity, specificity and clinical applicability of the immunohistochemical method is warranted. This revised version was published online in July 2006 with corrections to the Cover Date.     

Isolation of a novel simian T-cell lymphotropic virus from Pan paniscus that is distantly related to the human T-cell leukemia/lymphotropic virus types I and II.

An unusual serological profile against human T-cell leukemia/lymphotropic virus type I and II (HTLV-I and -II) proteins was reported in several human Pygmy tribes in Zaire and Cameroon with serum antibodies reactive with gp21 and p24. Here we describe a similar pattern of serum antibodies in a colony of captive pygmy chimpanzees and the isolation of a novel retrovirus, simian T-cell lymphotropic virus from Pan paniscus (STLVpan-p), from the peripheral blood mononuclear cells of several seropositive animals. Cocultures of peripheral blood mononuclear cells from three seropositive pygmy chimpanzees with human cord blood mononuclear cells led to the expression of an HTLV-I- and HTLV-II-related virus initially demonstrated by electron microscopy. Furthermore, several of these cocultures became immortalized T-cell lines expressing the CD4+ CD8+ DR+ phenotype of mature activated T cells. Southern blotting and DNA sequencing of a PCR fragment of viral DNA from these cell cultures demonstrated a distant evolutionary relationship of these viruses to HTLV-I and -II and distinct from the known STLV isolates. We designated this virus STLVpan-p. A genealogical analysis of the captive pygmy chimpanzees colony, originated from wild-caught animals, revealed a prevalence of seropositive offspring from infected mothers, as also observed with HTLVs. The presence in this old African Great Ape species of a virus which is genetically quite distinct from HTLV-I and -II could provide new insights in the phylogenesis of STLVs and HTLVs and be instrumental in the discovery of related human viruses.