Mycobacterium xenopi multiplies within human macrophages and enhances HIV replication in vitro

Mycobacterium xenopi can cause opportunistic infections, particularly in persons infected with human immunodeficiency virus type 1 (HIV-1). The primary focus of this effort was to determine if M. xenopi isolates could survive and grow in human peripheral blood macrophage (MPhi), and if these isolates could promote the replication of HIV-1 in vitro. M. xenopi bacilli survived and replicated 10-fold within 48 h in human MPhi while avirulent Mycobacterium smegmatis, did not grow within the MPhi. M. xenopi bacilli when cultured with peripheral blood mononuclear cells enhanced HIV-1 replication 30- and 50-fold with the macrophage-tropic HIV-1(Ba-L) and 50- and 75-fold with T-cell-tropic strain HIV-1(LAI) by 6 days post-infection when compared to M. smegmatis. The enhanced HIV replication was associated with increased production of TNF-alpha. Partial inhibition of HIV-1 induction was observed using a neutralizing anti-TNF-alpha monoclonal antibody, pentoxifylline, and matrix metalloproteinase (MMP) inhibitor I. Similar mechanisms of pathogenesis among mycobacterial species may help elucidate better treatment approaches in HIV co-infected persons.

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.

Effects of human T-lymphotropic virus type II on human immunodeficiency virus type 1 phenotypic evolution

Phenotypic change and broader coreceptor usage by HIV-1 have been associated with disease progression. HIV-1 coreceptor usage by primary isolates obtained from HIV-1-infected and HIV-1/HTLV-II-coinfected individuals was determined. HIV-1 was isolated from 15 of 20 HIV-1-infected and 17 of 24 HIV-1/HTLV-II-coinfected individuals. None of the isolates from either the HIV-1-infected or the coinfected group infected CCR5delta32 PBMCs, suggesting that they all were R5-tropic. Further, both spontaneous and PHA-stimulated production of MIP-1beta and RANTES were similar in HIV-1-infected and coinfected individuals. These data indicate that coinfection with HTLV-II has no effect on HIV-1 coreceptor usage or ex vivo beta-chemokine production.

HIV-specific cytotoxic T lymphocytes, HLA-A11, and chemokine-related factors may act synergistically to determine HIV resistance in CCR5 delta32-negative female sex workers in Chiang Rai, northern Thailand

Understanding how highly HIV-exposed individuals remain HIV uninfected may be useful for HIV vaccine design and development of new HIV prevention strategies. To elucidate mechanisms associated with resistance to HIV infection, immunologic and genetic factors were examined in 14 HIV-exposed but persistently seronegative (HEPS) female sex workers from Chiang Rai, northern Thailand and in ethnically matched, HIV-positive (n = 9) and HIV-negative women (n = 9). The HEPS women were identified in a study of commercial sex workers who had an HIV-1 incidence of 20.3 per 100 person-years. A high frequency of HLA-A11 was observed in HEPS women (86%) compared with northern Thai controls (56%). HIV-specific cytotoxic T lymphocyte (CTL) lytic responses were detected in cryopreserved peripheral blood mononuclear cells (PBMCs), using HLA-A-matched subtype E HIV-1 peptides in four of seven (57%) HEPS women, eight of eight HIV-positive women, and zero of nine HIV-negative unexposed controls (p = 0.019 HEPS women vs. HIV-negative controls). CTL lysis levels were low, but responses were detected to peptides from Nef, Pol, Gag, and Env. Nef responses predominated in HEPS women. Compared with controls, HEPS women tended to have higher frequencies of CCR5 promotor 59402GG and SDF-1 3'UTR 801A genotypes known to influence HIV transmission or course of disease. HEPS women also had higher levels of spontaneous RANTES production by PBMCs than other groups. Each of these factors could potentially contribute to HIV resistance. As most HEPS women had one or more of these factors, they may prevent HIV infection synergistically by blocking HIV cell entry, delaying its dissemination, or killing HIV-infected cells.

Cervical and prostate primary epithelial cells are not productively infected but sequester human immunodeficiency virus type 1

Primary prostate and cervical epithelial cells and epithelial cell lines were examined for human immunodeficiency virus type 1 (HIV-1) infection or transmission to peripheral blood mononuclear cells (PBMC). Neither cell-free nor cell-associated HIV-1 infected primary epithelial cells or cell lines. Pretreatment of HIV-1 to enhance CD4-independent entry did not augment infection. Cell surface expression was detected for galactosyl ceramide but not for CC-chemokine receptor 5, CXC-chemokine receptor 4, or CD4. The ability to transfer HIV-1 to resting or activated PBMC was tested by culturing with rinsed or trypsinized and replated HIV-1-exposed epithelial cells. Virus was not recovered from the rinsed or replated cocultures with resting PBMC; however, activated PBMC recovered HIV-1 from rinsed epithelial cells and rarely from replated epithelial cells. Although urogenital epithelial cells are not infected, these data suggest that they can transfer virus to activated immune cells and have implications for sexual transmission of HIV-1.

Involvement of matrix metalloproteinases in human immunodeficiency virus type 1-induced replication by clinical Mycobacterium avium isolates

The role of Mycobacterium avium isolates in modulating human immunodeficiency virus type 1 (HIV-1) replication was examined by use of an in vitro, resting T cell system. Two human clinical isolates (serotypes 1 and 4) but not an environmental M. avium isolate (serotype 2) enhanced HIV-1 replication. The M. avium-induced HIV-1 replication was not associated with cell activation or differential cytokine production or utilization. Addition of matrix metalloproteinase (MMP) inhibitors and their in vivo regulators, tissue inhibitors of metalloproteinases-1 and -2, abrogated M. avium-induced HIV-1 replication 80%-95%. The MMP inhibitors did not have any effect on the HIV-1 protease activity, suggesting that they may affect cellular processes. Furthermore, MMP-9 protein was differentially expressed after infection with clinical M. avium isolates and paralleled HIV-1 p24 production. Collectively, these data suggest that M. avium-induced HIV-1 replication is mediated, in part, through the induction of MMP-9.

Modulation of T-cell responses to a recall antigen in human T-cell leukemia virus type 1-infected individuals

To determine the mechanism of the purified protein derivative (PPD)-specific hyporesponsiveness in Mycobacterium bovis BCG-vaccinated human T-cell leukemia virus type 1 (HTLV-1)-infected individuals, we examined cytokine production in response to PPD in the following four groups of individuals: (i) HTLV-negative, PPD nonresponders (n = 11; NN); (ii) HTLV-negative, PPD responders (n = 18; NP); (iii) HTLV-positive, PPD nonresponders (n = 15; PN); and (iv) HTLV-positive, PPD responders (n = 15; PP). In vitro stimulation with PPD resulted in both proliferative responses and gamma interferon (IFN-gamma) production in NP and PP (P < 0.02), with minimal proliferation and IFN-gamma production in the NN and PN groups. Further, PPD-specific interleukin 10 (IL-10) production was significantly reduced in the PN group (P < 0.01), while the other groups had comparable levels. Cytokine reconstitution experiments demonstrated that while addition of recombinant IL-12 (rIL-12) plus anti-IL-4 restored PPD-specific responses in the NN group, it had no effect in the PN group. However, addition of rIL-12 resulted in the increased production of IFN-gamma in both nonresponder groups (NN and PN), suggesting that the lack of IFN-gamma production was not responsible for the PPD anergy. We conclude that PPD-specific anergy in HTLV-1-infected individuals appears to be due in part to their inability to respond to rIL-12.

Observed differences in virulence-associated phenotypes between a human clinical isolate and a veterinary isolate of Mycobacterium avium

Mycobacterium avium, the most common opportunistic pathogen in patients with AIDS, is frequently isolated from a variety of environmental sources, but rarely can these environmental isolates be epidemiologically linked with isolates known to cause human disease. Using a number of in vitro tissue culture assays, we found significant pathogenic differences between a serotype 4 human clinical M. avium isolate and a serotype 2 veterinary isolate. Cell association of the patient strain with a human intestinal cell line was 1.7 times that of the veterinary strain. Growth of this clinical strain in human peripheral blood mononuclear cell-derived macrophages increased from 12-fold higher than that of the veterinary isolate after 2 days to 200-fold higher after 4 days. By the conclusion of each experiment, lysis of all examined host cell types and accumulation of cell debris were observed in infections with the human isolate, but monolayers remained relatively intact in the presence of the animal isolate. The two strains also differed in the ability to stimulate human immunodeficiency virus replication in coinfected host cells, with p24 antigen levels after 6 days threefold higher in the cells coinfected with the clinical strain than in those infected with the veterinary strain. If the genetic differences responsible for the phenotypes observed in these assays can be identified and characterized, it may be possible to determine which M. avium strains in the environment are potential human pathogens.

Absence of human T-lymphotropic virus type I tax sequences in a population of normal blood donors in the Baltimore, MD/Washington, DC, area: results from a multicenter study

BACKGROUND

It was reported recently that sequences corresponding to the human T-lymphotropic virus type I (HTLV-I) tax gene were detected in peripheral blood mononuclear cells from 8 to 11 percent of healthy blood donors without detectable antibodies to HTLV-I. A multicenter blind study was conducted to determine if these results could be independently confirmed.

STUDY DESIGN AND METHODS

Specimens were collected from 100 anti-HTLV-I-negative healthy blood donors and from 11 anti-HTLV-I- or anti-HTLV-II-positive individuals. All samples were coded and distributed to each of four independent testing laboratories for polymerase chain reaction analysis to detect sequences of the HTLV-I or HTLV-II tax gene, using detailed procedures specified by the laboratory reporting the original observation. Each laboratory also tested a dilution panel of a plasmid containing HTLV-I tax to determine the analytical sensitivity of the procedure.

RESULTS

The analytical sensitivity of the screening methods permitted detection of as few as 1 to 10 copies of the tax gene. However, HTLV-I tax sequences could not be detected in any of the anti-HTLV-I-negative blood donors at more than one test site.

CONCLUSION

HTLV-I tax sequences appear not to be present in this population of 100 blood donors negative for anti-HTLV-I.

Activation of human T-cell leukemia virus type 1 tax gene expression in chronically infected T cells

Expression of human T-cell leukemia virus type 1 (HTLV-1) is regulated both by the HTLV-1 Tax transactivator and by cellular transcriptional factors binding to the viral long terminal repeat (LTR), suggesting that cellular signals may play a role in regulating viral expression. Treatment of cells chronically infected with HTLV-1, which express low levels of HTLV-1 RNAs and Tax protein, with phorbol esters (i.e., phorbol12-myristate 13- acetate [PMA]), phytohemagglutinin (PHA), sodium butyrate, or combinations of cytokines resulted in induction of HTLV- 1 gene expression. PMA or PHA treatment following cotransfection of HTLV-1 Tax expression plasmids resulted in synergistic activation of HTLV-1 LTR-directed gene expression, apparently involving tyrosine ki- nase- mediated pathways. These results suggest that cellular activation stimuli may cooperate with HTLV-1 Tax to enhance expression of integrated HTLV-1 genomes and thus may play a role in the pathogenesis of HTLV-1 disease.

Down-regulation of interleukin-10 expression and production is associated with spontaneous proliferation by lymphocytes from human T lymphotropic virus type II-infected persons

Cytokines from peripheral blood mononuclear cells (PBMC) from human T lymphotropic virus (HTLV)-II-infected persons were studied to delineate the mechanism(s) of spontaneous lymphocyte proliferation (SLP). Culturing HTLV-II-infected PBMC that spontaneously proliferate (SLP+) resulted in greater mRNA expression and production of interferon-gamma, interleukin (IL)-4, and IL-5, with a concomitant decrease in IL-10, than was seen with nonproliferating (SLP ) and normal PBMC. While IL-2 mRNA expression was higher, production was lower in SLP+ PBMC than in SLP and normal PBMC, implying that the proliferating cells are utilizing IL-2. Neutralization of IL-2 resulted in partial inhibition, suggesting that other cytokines also affect SLP. Addition of recombinant IL-10 inhibited the proliferation of SLP+ PBMC. Further, blocking costimulatory signals with monoclonal antibodies against CD80/CD86 resulted in increased IL-10 production with concomitant inhibition of SLP. The mechanism(s) underlying HTLV-II-associated SLP in vitro involve increased utilization of IL-2 and down-regulation of IL-10.

A flash-type bioluminescent immunoassay that is more sensitive than radioimaging: quantitative detection of cytokine cDNA in activated and resting human cells

Because of its high sensitivity, bioluminescence (BL) is an excellent alternative to radioactive quantitation of cytokine RT-PCR-derived products. BL also allows detection of amplicons at cycle numbers not normally detectable using radioactivity. No direct comparisons between these two methods have been made. In this study, the sensitivities of BL using recombinant aequorin, a flash-type luminescent tag capable of detecting signal to attomolar (10(-18) M) levels and radio imaging (RI) were directly compared. In addition, the application of BL for detecting cytokine message from biologic samples was examined. BL was 30- to 60-fold more sensitive than RI in detecting human IL-2 and CD3delta amplicons. This difference was particularly found during low cycle PCR, but was less at higher cycle numbers. The ability of BL to detect differences in cytokine message in stimulated and unstimulated human peripheral blood mononuclear cells was also evaluated. Using linear regression analysis, we observed up to 5,000-fold increases in RT-PCR amplified-mRNA in stimulated cells for IL-1alpha, IL-1beta, IL-2, IL-4, IL-5, IL-6, IL-10 and GM-CSF compared to unstimulated cells. Changes in CD3delta, TNF alpha or IL-12 were not observed or quantitated. We present a novel aequorin-based application of bioluminescent technology to directly quantitate RT-PCR amplicons and to investigate the induction of human cytokine expression. Significant advantages of this sensitive bioluminescent method compared with radioactive methods are its abilities to quantitate amplicons in a PCR cycle range where linear detection is most robust and to analyze products in an automated, open-architecture microtiter plate format.

Transcriptional activation of the intercellular adhesion molecule 1 (CD54) gene by human T lymphotropic virus types I and II Tax is mediated through a palindromic response element

In vitro infection of T cells with human T lymphotropic virus types I and II (HTLV-I and HTLV-II) resulted in constitutive expression of ICAM-1. Higher levels of ICAM-1 mRNA were expressed in HTLV-transformed cell lines (MT-2, MoT, C8166) when compared with uninfected T cell lines (A301). We demonstrate that this activation is conferred through a site on the ICAM-1 promoter that is activated in trans by the Tax protein of HTLV-I and HTLV-II. Enhanced promoter activity was detected when the ICAM-1 construct (-1162/+1) was transfected into HTLV-I-infected (MT-2), HTLV-II-infected (MoT, AI 1050), or an HTLV-I Tax-only-expressing (C8166) cell line as compared to the uninfected T cell line (A3.01). Cotransfection of the uninfected T cell line A3.01 with the ICAM construct along with Tax-I and Tax-II expression plasmid also resulted in increased promoter activity. Furthermore, experiments with deletion constructs of the ICAM-1 promoter region indicated that a region between -88 and -53 bp relative to the transcription start site is sufficient for Tax-inducible CAT expression. This segment includes an 11-bp palindromic segment (TTTCCGGGAAA) that has homology with the IFN-gamma and IL-6 response element. An 11-bp segment containing this regulatory region proved to be sufficient to confer Tax-I and Tax-II inducibility on a heterologous promoter (TK-CAT). Taken together these findings indicate that constitutive expression of ICAM-1 by HTLV-infected cells is influenced by the viral trans-activator protein Tax. This increased expression of ICAM-1 in response to the Tax protein may play an important role in the lymphoproliferation associated with HTLV infection.

Costimulatory effects of T cell proliferation during infection with human T lymphotropic virus types I and II are mediated through CD80 and CD86 ligands

The modulation of expression of CD80 and CD86 on T cells following infection with human T lymphotropic virus (HTLV)-I/II and its functional importance in T-T cell interactions was examined. Infection with HTLV-I/II leads to constitutive expression of CD80 and CD86, concomitant to down-modulation of CD28 on T cells. The CD80/CD86+ HTLV-infected T cells stimulated proliferation of allogeneic and autologous resting T cells, which could be specifically blocked by a soluble CTLA-4Ig chimeric protein, anti-CD80 or anti-CD86, but not by anti-CD54. It was necessary to inhibit interaction with both ligands (CD80 and CD86) to optimally block HTLV-mediated proliferation of allogeneic and autologous resting T cells. Simultaneous addition of anti-CD8O and anti-CD86 Abs also inhibited production of IFN-gamma, TNF-alpha, and IL-4, with no effect on IL-10 production, for both allo- and autologous T cell proliferation. Further, there was a direct correlation between the spontaneous proliferation of lymphocytes from patients infected with HTLV-II and expression of CD80, which could be blocked by simultaneous addition of anti-CD80 and anti-CD86. Taken together, these results suggest that HTLV-infected CD80/CD86+ T cells serve as APCs, leading to a sustained proliferation of T cells, and that both ligands participate in allostimulation, autologous proliferation, as well as spontaneous proliferation of HTLV-II-infected PBMC.

Costimulatory effects of T cell proliferation during infection with human T lymphotropic virus types I and II are mediated through CD80 and CD86 ligands

The modulation of expression of CD80 and CD86 on T cells following infection with human T lymphotropic virus (HTLV)-I/II and its functional importance in T-T cell interactions was examined. Infection with HTLV-I/II leads to constitutive expression of CD80 and CD86, concomitant to down-modulation of CD28 on T cells. The CD80/CD86+ HTLV-infected T cells stimulated proliferation of allogeneic and autologous resting T cells, which could be specifically blocked by a soluble CTLA-4Ig chimeric protein, anti-CD80 or anti-CD86, but not by anti-CD54. It was necessary to inhibit interaction with both ligands (CD80 and CD86) to optimally block HTLV-mediated proliferation of allogeneic and autologous resting T cells. Simultaneous addition of anti-CD8O and anti-CD86 Abs also inhibited production of IFN-gamma, TNF-alpha, and IL-4, with no effect on IL-10 production, for both allo- and autologous T cell proliferation. Further, there was a direct correlation between the spontaneous proliferation of lymphocytes from patients infected with HTLV-II and expression of CD80, which could be blocked by simultaneous addition of anti-CD80 and anti-CD86. Taken together, these results suggest that HTLV-infected CD80/CD86+ T cells serve as APCs, leading to a sustained proliferation of T cells, and that both ligands participate in allostimulation, autologous proliferation, as well as spontaneous proliferation of HTLV-II-infected PBMC.

Infection with human T-lymphotropic virus types I and II results in alterations of cellular receptors, including the up-modulation of T-cell counterreceptors CD40, CD54, and CD80 (B7-1)

To examine the phenotypic alterations associated with human T-lymphotropic virus types I and II (HTLV-I and -II) infection, long-term cell lines (n = 12 HTLV-I cell lines; n = 11 HTLV-II cell lines; n = 6 virus-negative cell lines) were analyzed for the cell surface expression of various lineage markers (i.e., myeloid, progenitor, and leukocyte), integrin receptors, and receptor-counterreceptor (R-CR) pairs responsible for cellular activation. As expected, all cell lines expressed the markers characterizing the leukocyte lineage (CD43, CD44, and CD53). Of the progenitor-myeloid markers examined (CD9, CD13, CD33, CD34, and CD63), only the percent expression of CD9 was significantly increased on HTLV-I and -II-infected cell lines as compared with that on virus-negative cell lines. Analysis of the beta 1 integrin subfamily (CD29, CD49b, CD49d, CD49e, and CD49f) showed no significant change, except that CD49e was significantly decreased on the HTLV-infected cell lines. For the beta 2 integrin subfamily, the cell surface density was increased for CD18 and CD11a, while the CD11c molecule was expressed exclusively on the HTLV-I- and HTLV-II-infected cell lines. Analysis of several R-CR pairs (CD2-CD58, CD45RO-CD22, CD5-CD72, CD11a-CD54, gp39-CD40, and CD28-CD80) demonstrated that comparable levels of expression of the Rs (CD2, CD45RO, CD5, and CD28) and of some of the CRs (CD58, CD22, and CD72) were in all cell lines; however, CD54, CD40, and CD80 were expressed constitutively on the HTLV-I- and HTLV-II-infected cell lines. Functionally, the expression of these R-CR pairs did not appear to affect the autologous proliferation since monoclonal antibodies to these R-CR pairs were not able to inhibit proliferation of the infected cell lines. Taken together, our results indicate that HTLV-I and -II can modulate the expression of several T-cell activation molecules and CRs normally expressed on alternate cell types.

Modulation of HTLV-II-associated spontaneous lymphocyte proliferation by beta 2 integrin CD11a/CD18 involves interaction with its cognate ligand, CD54

In vitro culture of lymphocytes from persons infected by human T-lymphocyte virus type II (HTLV-II) results in spontaneous proliferation in the absence of any exogenous stimuli. The present investigation examined the role of integrin molecules in spontaneous lymphocyte proliferation (SLP) in persons infected with HTLV-II (n = 18) and normal controls (n = 16). Phenotypic analysis of SLP cells on Day 8 demonstrated no change in the surface expression of CD29 (beta 1), CD49b,d,e, and f (alpha-chains) compared with cells from normal controls; however, there was an increase of CD29 expression on SLP cells on Day 8 (77.2 +/- 5.1%) compared with Day 0 (53.2 +/- 3.1%; P < 0.01). Furthermore, addition of extracellular matrix proteins, fibronectin, laminin, or collagen (beta 1 integrin ligands) did not alter either the proliferative responses or the adhesion clusters in either groups. Analysis of beta 2 integrins on SLP cells showed not only an increased cell surface density of both CD18 and CD11a but also differential expansion of CD8+ T-cells coexpressing CD18 (54.0 +/- 10.3%), CD11a (53.7 +/- 8.1%), and S6F1, an epitope of CD11a, (65.3 +/- 7.8%) on Day 8 compared with Day 0 (20.0 +/- 2.5%, 19.3 +/- 1.9%, and 38.0 +/- 7.0%, respectively). Monoclonal antibodies to CD18 and CD11a inhibited SLP by 55 +/- 6.3% in HTLV-II-infected persons in a dose-dependent manner. The inhibition of SLP by anti-beta 2 antibodies was not due to negative signaling, since these antibodies did not inhibit anti-CD3-stimulated proliferation of normal lymphocytes. Moreover, monoclonal antibodies to CD54, the ligand for CD11a, inhibited the SLP in the majority of HTLV-II-infected persons studied. Taken together, these data suggest that SLP by PBL from HTLV-II-infected individuals is mediated through increased expression of beta 2 integrins that can modulate cognate receptor/ligand interactions on the cell surface of autologous proliferating cells.

Cellular localization of CD4 in the human placenta. Implications for maternal-to-fetal transmission of HIV

CD4 is a 55-kDa glycoprotein that serves as an important cellular differentiation Ag and cell signaling protein on T lymphocytes, as well as a principal receptor for HIV-1 on a variety of cell types including lymphocytes. CD4 receptor expression in syncytiotrophoblasts, the principal cellular barrier in the human placenta, has not been clearly defined. Knowledge concerning the expression of the CD4 receptor on placental trophoblasts is important to define potential mechanisms of transmission of the virus between maternal blood and fetal tissues. Both mature and immature placenta (n = 10) were examined using an avidin D-based immunohistochemical procedure that permits clear morphologic distinction of cell types in placental sections. Syncytiotrophoblasts were defined using anti-cytokeratin mAb (AE1/3), whereas endothelial cells in placental villi were distinctly identified using a mAb directed to CD31. Placental Hofbauer cells (macrophages) and other leukocytes were identified by mAb staining of leukocyte common Ag (CD45). CD4 expression (identified by staining with three separate anti-CD4 mAb) was exclusively localized using this immunohistochemical method to leukocytes in placental villi (e.g., Hofbauer cells); however, no CD4 staining was evident in syncytiotrophoblasts, cytotrophoblasts, or villus endothelial cells. Furthermore, immunoaffinity-purified trophoblasts were negative for CD4 receptor expression. CD4 RNA was not identified in purified trophoblasts using both Northern blot assay and a sensitive polymerase chain reaction method to identify CD4 RNA. In addition, time course studies of purified trophoblasts immediately after purification and at 24, 48, and 72 h in culture indicated that CD4 RNA was not present as a transient, but labile transcript in trophoblasts. These data indicate that the transmission of HIV-1 across syncytiotrophoblasts may occur by mechanisms other than by binding the CD4 receptor and that tissue leukocytes (in particular Hofbauer cells) are likely the principal CD4+ cellular target of HIV-1 in the placenta.

Cellular localization of CD4 in the human placenta. Implications for maternal-to-fetal transmission of HIV

CD4 is a 55-kDa glycoprotein that serves as an important cellular differentiation Ag and cell signaling protein on T lymphocytes, as well as a principal receptor for HIV-1 on a variety of cell types including lymphocytes. CD4 receptor expression in syncytiotrophoblasts, the principal cellular barrier in the human placenta, has not been clearly defined. Knowledge concerning the expression of the CD4 receptor on placental trophoblasts is important to define potential mechanisms of transmission of the virus between maternal blood and fetal tissues. Both mature and immature placenta (n = 10) were examined using an avidin D-based immunohistochemical procedure that permits clear morphologic distinction of cell types in placental sections. Syncytiotrophoblasts were defined using anti-cytokeratin mAb (AE1/3), whereas endothelial cells in placental villi were distinctly identified using a mAb directed to CD31. Placental Hofbauer cells (macrophages) and other leukocytes were identified by mAb staining of leukocyte common Ag (CD45). CD4 expression (identified by staining with three separate anti-CD4 mAb) was exclusively localized using this immunohistochemical method to leukocytes in placental villi (e.g., Hofbauer cells); however, no CD4 staining was evident in syncytiotrophoblasts, cytotrophoblasts, or villus endothelial cells. Furthermore, immunoaffinity-purified trophoblasts were negative for CD4 receptor expression. CD4 RNA was not identified in purified trophoblasts using both Northern blot assay and a sensitive polymerase chain reaction method to identify CD4 RNA. In addition, time course studies of purified trophoblasts immediately after purification and at 24, 48, and 72 h in culture indicated that CD4 RNA was not present as a transient, but labile transcript in trophoblasts. These data indicate that the transmission of HIV-1 across syncytiotrophoblasts may occur by mechanisms other than by binding the CD4 receptor and that tissue leukocytes (in particular Hofbauer cells) are likely the principal CD4+ cellular target of HIV-1 in the placenta.

Characterization of human T-lymphotropic virus type I- and II-infected T-cell lines: antigenic, phenotypic, and genotypic analysis

Eighteen long-term T-cell lines were established from peripheral blood mononuclear cells of individuals infected with human T-lymphotropic virus type I (HTLV-I) or II (HTLV-II). These cell lines (10 HTLV-I and 8 HTLV-II), representing diverse pathologic profiles and geographic regions, have been in culture for over 6 months and have constitutively produced p24gag antigen. Antigenic characterization of the cell lines by Western blot analysis demonstrated that all but one produced gag (p24) and env (gp46 or gp52) structural proteins; one HTLV-I-infected cell line exhibited an aberrant protein profile. Phenotypic analysis of the HTLV-infected cell lines demonstrated phenotypes consistent with activated T-cells (CD5+, CD25+, HLA-DR+). The HTLV-I-infected cell lines were predominantly CD4+ (IR, FS, A212, SP, 1657, 1742, 3669, 1996, and 3614), whereas EG was CD8+. The HTLV-II-infected cell lines were either CD4+ (H2A, Y17, G12.1), CD8+ (H1H, H2E, Y03, Y06), or both (H1B). Restriction map analysis and subtyping of the viral genomes demonstrated heterogeneity among these isolates. Of the HTLV-I-infected cell lines, six were subtype II, one was subtype III and, on the basis of additional restriction sites, another subtype, tentatively classified as subtype IV, could be identified for three of the HTLV-I-infected cell lines. Of the HTLV-II-infected cell lines, six were subtype HTLV-IIa and two were subtype HTLV-IIb. While the majority of the cell lines resemble the prototypic HTLV-I-infected (MT-2) and HTLV-II-infected (MoT) cell lines, the antigenic, phenotypic, and genotypic data collectively demonstrate heterogeneity among viral isolates representing diverse geographic regions.

Characterization of a B-cell immunodominant epitope of human T-lymphotropic virus type 1 (HTLV-I) envelope gp46

The immune response elicited by a synthetic peptide derived from an immunodominant external envelope region (Env-5, amino acids 242-257) of human T-lymphotropic virus type 1 (HTLV-I) was tested in a rabbit model of HTLV-I infection. The synthetic peptide elicited a strong antibody response to the HTLV-I envelope protein gp46; however, these antibodies failed to inhibit HTLV-I-mediated cell fusion. Immunized rabbits were not protected from HTLV-I infection as determined by seroconversion to viral core proteins by immunoblot, HTLV-I p24 antigen detection in lymphocyte cultures and polymerase chain reaction for the HTLV-I provirus in lymphocyte DNA. Env-5 peptide immunization failed to induce T-cell lymphocyte proliferative responses in rabbits, but induced antibody responses in T-cell deficient Balb c nu/nu mice suggesting that the antigenic determinant represented by the Env-5 peptide is primarily a B-cell epitope. These results further define an immunodominant epitope of the HTLV-I envelope protein and suggest that potential synthetic peptide vaccines against HTLV-I infection must contain multiple antigens that induce both humoral and cellular immune reactivity.

Detection of simian T-lymphotropic virus type I using the polymerase chain reaction

To develop the polymerase chain reaction (PCR) for the detection of simian T-lymphotropic virus type I (STLV-I) infection, cell lines or peripheral-blood mononuclear cells (PBMC) from 2 non-human primate species [African green monkeys (AGM), Cercopithecus aethiops; baboon, Papio cynocephalus] were evaluated for their STLV-I status using oligonucleotide primer pairs and probes specific for the tax and pol gene regions of the closely related human T-lymphotropic virus type I (HTLV-I). These PCR results were compared with serologic (Western blot assay) and viral culture (p24-antigen capture assay) data. PCR products for both gene regions were detected in established baboon, Japanese macaque and rhesus macaque STLV-I-producing cell lines. STLV-I tax and pol products were also detected in PBMC from 4 of 4 infected AGM and 4 of 4 infected baboons, each of which were also Western-blot-positive and p24-antigen-capture-positive. Of the remaining AGM (n = 7) and baboon (n = 1) which were PCR-negative, each was also Western-blot-negative and p24-antigen-capture-negative. Two seronegative and virus-culture-negative AGM were classified as PCR indeterminate with weak reactivity using tax primers. These primer pairs failed to amplify DNA from uninfected human PBMC, an uninfected human lymphoid cell line, a simian immunodeficiency virus macaque (SIVmac251)-infected cell line and a simian-retrovirus-type-D(SRV-D)-infected cell line. HTLV-II-pol-specific primer pairs failed to amplify DNA from STLV-I-infected cell lines and PBMC from STLV-I-infected monkeys. Further, HTLV-I pol and tax primer pairs successfully amplified RNA from HTLV-I- and STLV-I-infected cell lines by reverse transcriptase (RT)-PCR. We have demonstrated excellent specificity in the detection of STLV-I by PCR using these HTLV-I-derived primers and probes. Additionally, our data suggest that the tax and pol gene regions are conserved between HTLV-I and STLV-I strains found among these diverse species of non-human primates.

A rapid microassay for measuring the luminol-dependent chemiluminescent response in canine whole blood

A microassay for the luminol-dependent chemiluminescence (CL) response in canine whole blood was developed to measure indirectly the oxidative metabolism of peripheral blood leukocytes. Fifty microliters of blood were mixed with 705 microliters of Hank's balanced salt solution containing 25 mM Hepes and 1.3 x 10(-4) M luminol. This mixture was allowed to equilibrate for 5 min after which 60 microliters of latex beads (0.801 microns diameter) were added as a stimulant, and the CL response was monitored continuously for 5 min at 37 degrees C using a luminometer. The whole blood CL response was significantly correlated (r = 0.784, P less than 0.01, n = 14) with the number of neutrophils in the peripheral blood. Further, the whole blood CL response was abolished by the depletion of neutrophils after passing the blood through an adherence column and by the addition of sodium azide. The relative chemiluminescent light unit (RCLU) was a reliable marker for comparing each peak value in different samples. The coefficient of variation (CV) of repetitive samples was 9.87%, and the CV of 14 normal dogs was 15.7%. This method is useful and applicable for screening the CL response in canine whole blood.

Lymphocyte and neutrophil dysfunction associated with hepatitis B virus and hepatitis non-A, non-B virus infection in the chimpanzee

Chimpanzees were examined for the effect of viral hepatitis infections on specific and nonspecific immune response mechanisms. The data suggest that infection with either hepatitis B virus or hepatitis non-A, non-B virus may result in suppression of cellular immune response components. Mitogen-induced lymphocyte proliferation was lower in virus-infected chimpanzees than in naive animals. Neutrophils from virus infected animals exhibited decreased or altered chemiluminescence kinetics.

Subunit vaccine protects Macaca nemestrina (pig-tailed macaque) against simian T-cell lymphotropic virus type I challenge

Five macaques received two vaccinations consisting of soluble human T-cell lymphotropic virus type I proteins from a cell/serum-free human T-cell lymphotropic virus type I-producing cell line. Five other macaques were vaccine controls. All were challenged with a simian T-cell lymphotropic virus type I-producing cell line. The vaccinated macaques generated a strong serological response to challenge as opposed to the control macaques. Western blot analysis of the sera showed that both groups recognized gag and env proteins, but the vaccinate's sera reacted better to the env proteins. Additionally, the antibody produced by both groups had antibody-dependent, complement-mediated cytotoxic activity toward both human and simian T-cell lymphotropic virus type I-infected target cells. The responses of lymphocytes and neutrophils, as measured by lymphocyte blast transformation and chemiluminescence response, respectively, showed no apparent difference between the vaccinates and controls. Testing for reverse transcriptase in lymphocyte supernatants revealed that the controls contained reverse transcriptase activity, while the vaccinates remained negative. The data presented here demonstrate that the vaccine was successful in protecting Macaca nemestrina from simian T-cell lymphotropic virus type I infection.

Inhibition of phorbol ester-induced neutrophil chemiluminescence by FeLV

Receptor-mediated activation is accompanied by phospholipid metabolism and by calcium fluctuation resulting in a chemiluminescence (CL) response in the neutrophil. This pathway involves activation of protein kinase C (PKC) and the NADPH oxidase. Artificial stimulants such as phorbol esters, specifically 12-O-tetradecanylphorbol-13-acetate (TPA), circumvent the receptor-mediated pathway and activate PKC resulting in a measurable CL response. Neutrophils from feline leukemia virus (FeLV) exposed cats were tested for their ability to generate a TPA-induced CL response. As compared to the non-FeLV-exposed specific-pathogen-free (SPF) control cat neutrophil CL responses, both viremic and nonviremic FeLV-exposed cats showed significant decreases in their CL responsiveness. Neither ultraviolet light-inactivated FeLV (UV-FeLV) nor protein components (FeLV-p15E and FeLV-p27) caused a significant decrease in the CL responses of the SPF cat neutrophils. The suppressed TPA-induced CL response from FeLV-infected cats may involve an intracellular mechanism not affected in vitro by exposure of the neutrophil to the virus or viral components.

FeLV-induced immunosuppression through alterations in signal transduction: down regulation of protein kinase C

Activation of protein kinase C by a phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (TPA), was shown to stimulate the respiratory burst in normal cat neutrophils. Neutrophils from feline leukemia virus (FeLV)-exposed viremic and nonviremic cats had significant suppression of their respiratory burst when stimulated with TPA. The addition of whole ultraviolet light-inactivated FeLV and FeLV proteins to normal cat neutrophils produced no significant suppression of the respiratory burst. These data suggest two possible mechanisms for suppression. The first is partially due to viral alterations of the neutrophil as seen in viremic cats, but, because exogenously applied FeLV or FeLV proteins had no effect on the respiratory burst, an additional mechanism is present. The second mechanism may be caused by a latent FeLV infection residing in nonviremic cat bone marrows which alters their immune system, resulting in immunosuppression.

FeLV-induced immunosuppression through alterations in signal transduction: changes in intracellular free calcium levels

Feline leukemia virus (FeLV) is a retrovirus with immunosuppressive properties. The mechanism(s) of immunosuppression is unknown. Calcium has been shown to be a second messenger in cellular activation and regulation. This study was designed to determine whether FeLV alters intracellular free calcium (IFC) levels in an FeLV-infected feline lymphoid cell line. Control cells and FeLV-infected cells were exposed to Concanavalin A, formyl-L-methionyl-L-leucyl-L-phenylalanine, and leukotriene B4. The basal IFC and post-stimulation IFC levels were recorded using Fura 2 AM and a luminescence spectrometer. Data collected indicate that FeLV-infected cells have a higher basal level of IFC and a reduced amount of increase in IFC after stimulation when compared to the control cells. The results would seem to indicate retrovirus-mediated interference occurring in the intracellular calcium signaling process.

Immunodeficiency in latent feline leukemia virus infections

Challenge of naive experimental animals with a retroviral inoculum may result in one of two broad sequelae. The first is the establishment of an appropriate humoral and cellular immune response leading to a condition of immunity to subsequent infection with the retrovirus. Alternatively, the host may fail to develop a successful immune response, resulting in a chronic viremia associated with immunosuppression and ultimately death due to secondary pathogens. An alternate disease course is the establishment of a latent infection characterized by the presence of neutralizing antibody and strong cellular immune reactivity. Recent data from the feline leukemia virus (FeLV) system suggest that cats infected with this virus may develop immunosuppression in the form of persistent neutrophil dysfunction. The potential effect of this cellular dysfunction is the possible susceptibility of the host to the same opportunistic pathogens which are responsible for the increased mortality noted in chronic FeLV infections. These data demonstrate that persistent retroviremia is not essential for the establishment of immunosuppression. This overview presents data accumulated from the feline model of the human acquired immunodeficiency syndrome (AIDS) and discusses its relationship to human retroviral infections.