HIV-1 in trophoblastic and villous Hofbauer cells, and haematological precursors in eight-week fetuses

In vitro infection of human placental trophoblast by wild-type vaccinia virus and recombinant virus expressing HIV envelope glycoprotein

Short-time (< or = 7 days) cultures of trophoblast mononuclear cells isolated from term placentae were challenged with vaccinia virus. Cytopathic effects were induced in crude placental cell preparations as well as in cultures established after negative immunosorting of major histocompatibility complex class I epitope-expressing cells, i.e. cultures exclusively derived from villous cytotrophoblast according to our present state of knowledge. The trophoblast in vitro supported a full replicative cycle of both wild-type viruses and a recombinant clone serving as a vector for the human immunodeficiency virus type 1 envelope gene. Results may shed light on mechanisms involved in the rarely observed foetal damage caused by smallpox vaccination during pregnancy.

Laboratory methods for early detection of human immunodeficiency virus type 1 in newborns and infants

Cumulative data on serological testing of newborns and infants have shown that (i) maternal and newborn anti-HIV-1 IgG titers are high at delivery, which may explain the persistence of antibody in the infants of seropositive mothers; (ii) in some situations, serial HIV-1 antibody testing may identify infected infants; and (iii) detection of anti-HIV-1 IgA or IgM is specific for infection but the sensitivity of this assay may be compromised in certain situations, such as when infected infants are hypogammaglobulinemic or when the rise and fall of HIV-1-specific IgM synthesis following acute infection has been completed before delivery of the infant. Cumulative data on PCR, viral culture, and tests for antigen in newborns and infants have shown that (i) among all age groups, viral culture is probably the most specific test available for detection of HIV-1, as PCR and the p24 antigen test may (though rarely) give false-positive results; (ii) the sensitivity of these tests increases in the order of antigen, culture, and PCR, with relatively insensitive results in the first 3 months of life for all of these tests; (iii) the sensitivity of all of these tests improves and approximates 90 to 100% when infants over 6 months of age are tested; and (iv) data regarding the sensitivity, specificity, and usefulness of these virological assays in infants under 3 months of age are very scant and inconclusive.

Vertical transmission of human immunodeficiency virus (HIV) infection. Reactivity of maternal sera with glycoprotein 120 and 41 peptides from HIV type 1

The observation that approximately 70% of HIV-infected pregnant women do not transmit infection vertically suggests that antibody therapy may be effective in the prevention of transmission of HIV infection from mother to child. Currently, there is an incomplete understanding of the processes involved in vertical transmission of HIV infection. The elucidation of the serological basis of maternal immunity as it relates to protection from vertical transmission is the goal of this study. We have screened 20 maternal sera from HIV+ individuals of known vertical transmission status for reactivity with 31 peptides spanning the entire envelope glycoprotein of HIV-1. Of interest was reactivity to regions outside of the V3 loop of gp120. The findings have been examined in relationship to transmission status, as well as to in vitro anti-HIV-1 biological activity. Our results indicate that lack of vertical transmission is correlated with high viral neutralization activity, but not with antisyncytial activity nor with binding to the V3 peptides examined in this study. Also, the transmission group bound to fewer gp41 peptides when compared with the nontransmission group, suggesting that immune responses to gp41 may be important in preventing transmission. These findings may provide insights into the design of passive immunotherapies.

Primary cultures of endothelial cells from the human liver sinusoid are permissive for human immunodeficiency virus type 1

Human endothelial cells isolated from hepatic sinusoids were infected in vitro with human immunodeficiency virus type 1 (HIV-1). An early sign of infection occurring in the culture was the formation of multinucleated cells. By double-labeling immunofluorescence, 5-15% of the cells recognized as endothelial cells owing to the presence of von Willebrand factor were found to contain HIV p24 and gp120 antigens after 2 weeks. Reverse transcriptase activity was released into the medium, and different steps in the process of viral budding were observed by electron microscopy. The virus produced by the endothelial cells was found to be infectious for CEM cells, a human T-cell line. CD4 molecules are present at the surface of the endothelial cells, as demonstrated by immunogold-silver staining and backscattered electron imaging. Treatment with an anti-CD4 antibody abolished productive infection of the sinusoidal endothelial cells. The possibility that endothelial cells of the liver sinusoid are infected in vivo with HIV remains to be clearly shown.

Immunohistochemical localization of human immunodeficiency virus p24 antigen in placental tissue

As human immunodeficiency virus (HIV) infection spreads into the heterosexual population, perinatally acquired HIV infection will increase in incidence, and knowledge of the mechanism of this transfer is important. We have used immunoperoxidase techniques to detect HIV p24 antigen in formalin-fixed, paraffin-embedded placental tissue from nine known HIV serologically positive mothers. In four of these cases we have detected evidence or viral antigen in placental Hofbauer cells, vascular endothelium, or intermediate trophoblast. The implications for understanding the mode of transfer of infection to the fetus are discussed.

Human trophoblast cells express CD4 and are permissive for productive infection with HIV-1

The European collaborative study of HIV-infected pregnant women in Europe now indicates a 13% risk of fetal HIV infection (originally thought to be about 30%, and possibly higher in some countries). Several reports suggest trans-placental passage. However, the detailed mechanisms associated with such vertical transmission have not yet been clarified. We have examined the possibility that HIV enters placental tissue from maternal blood via binding to CD4 and Fc receptors (FcR) at the trophoblast level, allowing intraplacental infection. Here we report the detection of several FcR with distinct localization in the placental villus as well as CD4 surface expression on human trophoblast cells. In addition, we show that trophoblastic cells interact specifically with the gp120/gp160 viral envelope protein. By their tissue localization, these receptors could be responsible for the entry of HIV into the fetal placental cells. Furthermore, purified placental cells can be directly infected by HIV in vitro, and the infection is inhibited by soluble CD4. This suggests a crucial role of the CD4 receptor but an additional way of entry cannot be excluded. Such an in vitro model may be suitable for further studies concerning placental HIV transmission and its prevention.

Vertical transmission

Since AIDS was first described in children, much has been learnt about the epidemiology, clinical presentations and natural history of perinatally acquired HIV disease. As yet, several questions remain unanswered about the pathogenesis of vertical transmission, the relative risk associated with each mode of transmission, the rate of transmission from mother to child, and the factors that might contribute to the efficiency of transmission. Data presented thus far suggest that intrauterine exposure poses the greatest risk, but more recent reports have reopened speculation that infection could occur at or around the time of delivery. The prospects for intervention, to stop transmission from mother to child, rest on the ability to identify HIV-infected women; the knowledge of how and when the virus infects the fetus; and how to identify, as early as possible, those truly infected infants. Resources should therefore be set aside for routine screening for HIV in antenatal women. There is also a need to quantify the contribution made by intrauterine versus intrapartum events. Lastly, promising new techniques designed to detect neonatal HIV infection must be properly evaluated against standard methods, and correlated with clinical outcome. Only then can the efficacy of antiretroviral therapy be tried, to prevent vertical transmission.

Possible transplacental transmission of human papillomaviruses

OBJECTIVE

The objective of this study was to examine the possibility of intrauterine human papillomavirus infection of fetuses by transplacental transmission of human papillomavirus before delivery.

STUDY DESIGN

Specimens of cervicovaginal cells and peripheral blood mononuclear cells were obtained from 52 consecutive pregnant women in the third trimester of pregnancy. Cord blood specimens were also obtained from the neonates born to these mothers. Presence of human papillomavirus types 16 and 18 deoxyribonucleic acid was analyzed by an in vitro enzymatic deoxyribonucleic acid amplification method.

RESULTS

Human papillomavirus type 16 deoxyribonucleic acid was found in 6 (11.5%) cervicovaginal and in 9 (17.3%) peripheral blood mononuclear cell specimens. Seven cord blood specimens from neonates born to mothers who were positive for peripheral blood mononuclear cell human papillomavirus type 16 deoxyribonucleic acid were found to contain human papillomavirus type 16 deoxyribonucleic acid. One cervicovaginal and two peripheral blood mononuclear cell specimens contained human papillomavirus type 18 deoxyribonucleic acid, but none of the cord blood specimens contained human papillomavirus type 18 deoxyribonucleic acid.

CONCLUSION

These results seem to suggest possible transplacental transmission of the virus and the potential association of such transmission with the status of human papillomavirus in peripheral blood mononuclear cells.

High risk of HIV-1 infection for first-born twins. The International Registry of HIV-exposed Twins

To examine the epidemiology and natural history of mother-to-infant transmission of human immunodeficiency virus type 1 (HIV-1), especially genetic and intrapartum exposure factors, we obtained data on twins and triplets born to women infected with the virus. 40 investigators in nine countries contributed demographic, clinical, and epidemiological data on 100 sets of twins and 1 set of triplets. Among the 66 evaluable sets, HIV-1 infection was more common in first-born than in second-born twins (p = 0.004). In 22 sets, only one twin was infected (18 first-born, 4 second-born). 50% of first-born twins delivered vaginally and 38% of first-born twins delivered by caesarean were infected, compared with 19% of second-born twins delivered by either route. HIV-1 infection status tended to be concordant in more monozygotic (14 of 17 sets) than dizygotic (26 of 43) sets, but the frequency and clinical signs of HIV-1-related disease were similar in only 3 of the 10 sets with both children infected. These findings suggest that some infants may be infected in utero before labour but that a substantial proportion of HIV-1 transmission occurs as the first twin encounters the cervix and birth canal. Such measures as cleansing of the birth canal and caesarean delivery before membrane rupture might reduce the risk of transmission for infants born to HIV-1-infected women and should be the subjects of controlled clinical trials. Caesarean section should not be regarded as a wholly preventive measure, however, since substantial proportions of both first-born and second-born twins delivered in this way were infected.

Intracellular sequestration and transmission of HIV-1 in pregnancy

30-50% of infants born to HIV-1 seropositive mothers are infected. Although a vertical transmission of the virus to the foetus via trophoblastic cells and mechanisms of its access thereof have been made, one of several questions which remains is: how do HIV-1 infected cells of monocyte/macrophage (MM) lineage, i.e. Hofbauer cells, which facilitate viral transmission, avoid cytolytic destruction vs. that which occurs in infected CD4+ T-cells and serve as a reservoir for virus, wherein it replicates? Recent studies of transglutaminases (TGases), a ubiquitous family of Ca(2+)-dependent peptide ligases catalyzing the post-translational covalent cross-linking of proteins and incorporation of amines into proteins have revealed a unique spectrum of immunoregulatory (IR) properties. In consonance with these studies, the biochemical and immunohistochemical identification of decidual and placental TGases, and their associated IR properties, and earlier studies of uterine and placental macrophages, a hypothesis is purposed to account for the intracellular assembly and accumulation of HIV-1 within cells of MM lineage, and transmission therefrom, in pregnancy.

HIV-I infection in perinatally exposed siblings and twins. The Italian Register for HIV Infection in Children

In a multicentre study on perinatal HIV-I infection including 1493 children born from 1471 pregnancies to 1415 infected mothers, 22 twin pairs and 56 sibships (115 children) were recorded. The frequency of twin pregnancies was 1.5 (22/1471) and 3.9% (56/1415) seropositive women had more than one at risk pregnancy. In 18 twin pairs with a known infection status nine of the 36 children (25%) were infected. Discordance in infection status was present in only one (5.5%) dizygous pair. A high relative risk of infection (23.1) in a twin was observed when the other was infected. Infection was unrelated to gestational age, mode of delivery, or birth weight. Infection status was defined in 41 sibships (84 children including one first born twin pair and one third born child). When the first born was infected, 11/26 (42.3%) second born children were also infected, whereas this happened in only 2/16 (12.5%) second or third born children when the first born was uninfected. Two out of nine first born (22.2%) and 5/21 (23.8%) second born children prospectively followed up from birth acquired the infection. Results of this study demonstrate that neither twin nor second pregnancies are at increased risk of mother to child HIV-I transmission. Overall data suggest that non-casual factors in mother and/or child influence perinatal infection.

Cell-mediated infection of human placental trophoblast with HIV in vitro

In order to investigate how human immunodeficiency virus (HIV) gains entry to the placenta, we have performed in vitro experiments in which highly purified trophoblast cells isolated from term human placentas were examined for their susceptibility to HIV infection. Trophoblast cells were exposed to cell-free HIV-1 for up to 24 h, after which the cultures were monitored by p24 antigen capture assay, reverse transcriptase assay, and electron microscopy for evidence of virus uptake and replication. None was found. In the second series of experiments, trophoblast cells were cocultured with HIV-infected MOLT-4 cells for 24 h, stained using an anti-HIV antibody, and examined by immunofluorescence microscopy. The MOLT cells were strongly positive, as expected, but many trophoblast colonies also showed a punctate staining pattern. Examination of similar cultures using the electron microscope revealed MOLT cells adherent to trophoblast but no evidence of cell-cell fusion. Virions were observed in coated pits at the trophoblast cell surface and in endosomes or multivesicular bodies in the cytoplasm. These observations are consistent with an endocytosis-mediated mechanism of virus entry. Virions were also observed budding from the trophoblast plasma membrane, indicating that these cells can support HIV replication. To our knowledge, these results show for the first time that HIV can infect placental trophoblast cells in vitro. The results suggest that the placenta could become infected with HIV by the interaction of virus-infected maternal lymphocytes with syncytiotrophoblast bordering the maternal blood in the intervillous space.

Human immunodeficiency virus type 1 infection of human placenta: potential route for fetal infection

To determine the potential role of the placenta in transmission of human immunodeficiency virus (HIV) from mother to fetus, the ability of human placental tissue to support HIV type 1 (HIV-1) infection was examined. HIV-1-seronegative first-trimester placentas were maintained in culture and infected with HIV-1. Virus production, measured by HIV-1 antigen release into the supernatant, and HIV-1 DNA, identified by polymerase chain reaction, were detected for at least 12 days postinfection. Western immunoblot analysis showed Gag proteins, precursor p55, and cleavage products p24 and p17 in HIV-1-infected tissues. Double labeling of placental villi with antibodies to CD4 and placental trophoblast-specific alkaline phosphatase indicated that trophoblasts express CD4 antigen. Additionally, immunostaining of HIV-1-infected tissues with anti-p24 antibodies demonstrated HIV-1 protein expression in placental trophoblasts. Evaluation of human chorionic gonadotropin and progesterone production by the placental cultures indicated that there was a 90% decrease in human chorionic gonadotropin and a 70% decrease in progesterone production in HIV-1-infected cultures in comparison with controls. These data demonstrate that trophoblastic cells of human placenta tissue express CD4 and are susceptible to HIV-1 infection; also, placental endocrine function is decreased by HIV-1 infection. Thus, the placenta may serve as a reservoir of HIV-1 infection during pregnancy contributing to infection of the fetus, and decreased placental hormone production may result in impaired fetal development.

Human transformed trophoblast-derived cells lacking CD4 receptor exhibit restricted permissiveness for human immunodeficiency virus type 1

We investigated the nature of interaction of the malignantly transformed cell lines of trophoblast origin BeWo, JAR, and JEG-3 with three different human immunodeficiency virus type 1 (HIV-1) isolates (RF, 3B, and NDK). After inoculation with cell-free virus, the persistence of infection was determined for 1 month by monitoring the presence of viral DNA in the cells by the polymerase chain reaction (PCR). Furthermore, the infectious virus in the culture supernatant was assayed with CEM-SS cells, and attempts to rescue the virus by cocultivation with CEM-SS cells were made. Appraised on the basis of the relative amount of viral DNA and the frequency of positive cocultivation. JEG-3 was the most permissive and BeWo was the least permissive cell line. However, when the cells were transfected with two biologically active molecular clones of HIV-1, the BRU and NDK isolates, all three cell lines turned out to support the production of mature virus progeny to the same extent. The abundance of viral DNA sequences in the infected cells varied with the isolate, showing an overall decline from RF to NDK. The amount of viral DNA in the cells and its expression decreased during the period of observation; this decrease was mirrored in an erosion of the virus recovery rate at cocultivation from 71% recovery on day 8 to failure of isolation on day 32. None of the cell lines expressed detectable amounts of cell surface CD4 molecules when assayed by flow microfluorometry and direct radioimmunoassay. Northern (RNA) blot hybridization analysis of both the total RNA and the mRNA did not reveal any CD4-specific message: nonetheless, by using the PCR, sequences specifically related to the CD4 gene were uncovered. The data demonstrate that the trophoblast-derived cell lines are susceptible to infection with HIV and that they support transient viral replication in the initial phases of infection. However, the latent form of infection may persist over a period of several weeks.

Viral infections of the developing nervous system

Both clinical and experimental studies indicate that viruses can interact with the developing nervous system to produce a spectrum of neurological damage and brain malformations. Following infection of the pregnant woman, virus may indirectly or directly involve the fetus. Direct involvement is generally due to transplacental passage of the virus and invasion of fetal tissue. Resultant disease is determined by a variety of virus-host factors, including the developmental stage of the fetus at the time it is infected, the neural cell populations which are susceptible to infection, the consequent virus-infected cell interactions, and the mechanism and timing of viral clearance. There is a growing list of human viruses which injure the developing nervous system. There are also several experimental models in which congenital viral infections have been shown to result in a variety of brain malformations but with no evidence of the prior infection remaining at the time of birth.

Replication of human immunodeficiency virus type 1 in primary cultured placental cells

The role of placental cells in transplacental transmission of human immunodeficiency virus type 1 (HIV 1) was investigated. Placental macrophages and trophoblasts, which together represent the main cell components of the placenta, were cultivated separately and then compared to foetal monocyte-derived macrophages for susceptibility to HIV 1 infection. Placental macrophages treated with granulocyte-macrophage colony-stimulating factor (GM-CSF) were less easily infected with HIV 1 than were GM-CSF-treated foetal monocyte-derived macrophages. HIV 1 replication in cocultures consisting of infected placental macrophages together with a highly HIV 1-permissive cell line (CEM) was detected persistently for at least 6 weeks by reverse transcriptase assay, even though placental macrophages expressed no detectable CD4 receptor, as indicated by indirect immunofluorescence. HIV 1-specific DNA sequences were also detected in infected placental macrophages. Trophoblasts exhibited no detectable CD4 expression and did not support the replication of HIV 1, although low levels of HIV 1-specific DNA sequences could be detected in infected trophoblasts. Placental macrophages or trophoblasts (or both) may thus play an important role in transplacental HIV 1 transmission.

Epidemiology of pediatric HIV infection

Perinatal transmission of human immunodeficiency virus (HIV) continues to increase. In 1989 alone, it is estimated that 1750 infected children were born in the United States. Although transmission is spreading to areas outside the cities originally most affected, these cities continue to bear the greatest toll. Adolescents may be particularly vulnerable to HIV infection; education and counseling are critical for controlling the epidemic in this age group.