Correlation of virus load and soluble L-selectin, a marker of immune activation, in pediatric HIV-1 infection

The Role of L-Selectin in HIV Infection

HIV envelope glycoprotein is the most heavily glycosylated viral protein complex identified with over 20 glycans on its surface. This glycan canopy is thought to primarily shield the virus from host immune recognition as glycans are poor immunogens in general, however rare HIV neutralizing antibodies nevertheless potently recognize the glycan epitopes. While CD4 and chemokine receptors have been known as viral entry receptor and coreceptor, for many years the role of viral glycans in HIV entry was controversial. Recently, we showed that HIV envelope glycan binds to L-selectin in solution and on CD4 T lymphocytes. The viral glycan and L-selectin interaction functions to facilitate the viral adhesion and entry. Upon entry, infected CD4 T lymphocytes are stimulated to progressively shed L-selectin and suppressing this lectin receptor shedding greatly reduced HIV viral release and caused aggregation of diminutive virus-like particles within experimental infections and from infected primary T lymphocytes derived from both viremic and aviremic individuals. As shedding of L-selectin is mediated by ADAM metalloproteinases downstream of host-cell stimulation, these findings showed a novel mechanism for HIV viral release and offer a potential new class of anti-HIV compounds.

Intestinal Damage and Inflammatory Biomarkers in Human Immunodeficiency Virus (HIV)-Exposed and HIV-Infected Zimbabwean Infants

Background

Disease progression is rapid in human immunodeficiency virus (HIV)–infected infants. Whether intestinal damage and inflammation underlie mortality is unknown.

Methods

We measured plasma intestinal fatty acid binding protein (I-FABP), soluble CD14 (sCD14), interleukin 6 (IL-6), and C-reactive protein (CRP) at 6 weeks and 6 months of age in 272 HIV-infected infants who either died (cases) or survived (controls), and in 194 HIV-exposed uninfected (HEU) and 197 HIV-unexposed infants. We estimated multivariable odds ratios for mortality and postnatal HIV transmission for each biomarker using logistic regression.

Results

At 6 weeks, HIV-infected infants had higher sCD14 and IL-6 but lower I-FABP than HIV-exposed and HIV-unexposed infants (P < .001). CRP was higher in HIV-exposed than HIV-unexposed infants (P = .02). At 6 months, HIV-infected infants had highest sCD14, IL-6, and CRP concentrations (P < .001) and marginally higher I-FABP than other groups (P = .07). CRP remained higher in HIV-exposed vs HIV-unexposed infants (P = .04). No biomarker was associated with mortality in HIV-infected infants, or with odds of breast-milk HIV transmission in HIV-exposed infants.

Conclusions

HIV-infected infants have elevated inflammatory markers by 6 weeks of age, which increase over time. In contrast to adults and older children, inflammatory biomarkers were not associated with mortality. HEU infants have higher inflammation than HIV-unexposed infants until at least 6 months, which may contribute to poor health outcomes.

Brief Report: L-Selectin (CD62L) Is Downregulated on CD4+ and CD8+ T Lymphocytes of HIV-1-Infected Individuals Naive for ART

The expression of L-selectin (CD62L) in HIV-1 infection has not been extensively investigated. Here, we measured CD62L expression on T-cell subsets of HIV-1-infected individuals naive for antiretroviral therapy (ART-naive) or receiving therapy (ART), and seronegative control subjects (HIV-neg). We found reduced frequencies of CD62L(+) cells among CD4(+) and CD8(+) T cells from ART-naive as compared with ART and HIV-neg groups, particularly within naive and central memory subsets. CD62L expression on T cells inversely correlated with viral load and rapidly increased after ART initiation. Plasma sCD62L levels did not correlate with CD62L expression, being higher in all HIV-1-infected individuals as compared with HIV-neg subjects. Finally, CD62L downregulation was found associated with the expression of the CD38 activation marker in CD8(+) T cells, but not in CD4(+) T cells. We suggest that CD62L downregulation due to unconstrained HIV-1 replication may have important consequences for T-cell circulation and function and for disease progression.

Baseline Inflammatory Biomarkers Identify Subgroups of HIV-Infected African Children With Differing Responses to Antiretroviral Therapy

BACKGROUND

Identifying determinants of morbidity and mortality may help target future interventions for human immunodeficiency virus (HIV)-infected children.

METHODS

CD4(+) T-cell count, HIV viral load, and levels of biomarkers (C-reactive protein, tumor necrosis factor α [TNF-α], interleukin 6 [IL-6], and soluble CD14) and interleukin 7 were measured at antiretroviral therapy (ART) initiation in the ARROW trial (case-cohort design). Cases were individuals who died, had new or recurrent World Health Organization clinical stage 4 events, or had poor immunological response to ART.

RESULTS

There were 115 cases (54 died, 45 had World Health Organization clinical stage 4 events, and 49 had poor immunological response) and 485 controls. Before ART initiation, the median ages of cases and controls were 8.2 years (interquartile range [IQR], 4.4-11.4 years) and 5.8 years (IQR, 2.3-9.3 years), respectively, and the median percentages of lymphocytes expressing CD4 were 4% (IQR, 1%-9%) and 13% (IQR, 8%-18%), respectively. In multivariable logistic regression, cases had lower age-associated CD4(+) T-cell count ratio (calculated as the ratio of the subject's CD4(+) T-cell count to the count expected in healthy individuals of the same age; P < .0001) and higher IL-6 level (P = .002) than controls. Clustering biomarkers and age-associated CD4(+) and CD8(+) T-cell count ratios identified 4 groups of children. Group 1 had the highest frequency of cases (41% cases; 16% died) and profound immunosuppression; group 2 had similar mortality (23% cases; 15% died), but children were younger, with less profound immunosuppression and high levels of inflammatory biomarkers and malnutrition; group 3 comprised young children with moderate immunosuppression, high TNF-α levels, and high age-associated CD8(+) T-cell count ratios but lower frequencies of events (12% cases; 7% died); and group 4 comprised older children with low inflammatory biomarker levels, lower HIV viral loads, and good clinical outcomes (11% cases; 5% died).

CONCLUSIONS

While immunosuppression is the major determinant of poor outcomes during ART, baseline inflammation is an additional important factor, identifying a subgroup of young children with similar mortality. Antiinflammatory interventions may help improve outcomes.

HIV-1 Nef and Vpu Interfere with L-Selectin (CD62L) Cell Surface Expression To Inhibit Adhesion and Signaling in Infected CD4+ T Lymphocytes

Leukocyte recirculation between blood and lymphoid tissues is required for the generation and maintenance of immune responses against pathogens and is crucially controlled by the L-selectin (CD62L) leukocyte homing receptor. CD62L has adhesion and signaling functions and initiates the capture and rolling on the vascular endothelium of cells entering peripheral lymph nodes. This study reveals that CD62L is strongly downregulated on primary CD4(+) T lymphocytes upon infection with human immunodeficiency virus type 1 (HIV-1). Reduced cell surface CD62L expression was attributable to the Nef and Vpu viral proteins and not due to increased shedding via matrix metalloproteases. Both Nef and Vpu associated with and sequestered CD62L in perinuclear compartments, thereby impeding CD62L transport to the plasma membrane. In addition, Nef decreased total CD62L protein levels. Importantly, infection with wild-type, but not Nef- and Vpu-deficient, HIV-1 inhibited the capacity of primary CD4(+) T lymphocytes to adhere to immobilized fibronectin in response to CD62L ligation. Moreover, HIV-1 infection impaired the signaling pathways and costimulatory signals triggered in primary CD4(+) T cells by CD62L ligation. We propose that HIV-1 dysregulates CD62L expression to interfere with the trafficking and activation of infected T cells. Altogether, this novel HIV-1 function could contribute to virus dissemination and evasion of host immune responses.

IMPORTANCE

L-selectin (CD62L) is an adhesion molecule that mediates the first steps of leukocyte homing to peripheral lymph nodes, thus crucially controlling the initiation and maintenance of immune responses to pathogens. Here, we report that CD62L is downmodulated on the surfaces of HIV-1-infected T cells through the activities of two viral proteins, Nef and Vpu, that prevent newly synthesized CD62L molecules from reaching the plasma membrane. We provide evidence that CD62L downregulation on HIV-1-infected primary T cells results in impaired adhesion and signaling functions upon CD62L triggering. Removal of cell surface CD62L may predictably keep HIV-1-infected cells away from lymph nodes, the privileged sites of both viral replication and immune response activation, with important consequences, such as systemic viral spread and evasion of host immune surveillance. Altogether, we propose that Nef- and Vpu-mediated subversion of CD62L function could represent a novel determinant of HIV-1 pathogenesis.

Involvement of neutrophil hyporesponse and the role of Toll-like receptors in human immunodeficiency virus 1 protection

OBJECTIVES

Neutrophils contribute to pathogen clearance through pattern recognition receptors (PRRs) activation. However, the role of PRRs in neutrophils in both HIV-1-infected [HIV-1(+)] and HIV-1-exposed seronegative individuals (HESN) is unknown. Here, a study was carried out to evaluate the level of PRR mRNAs and cytokines produced after activation of neutrophils from HIV-1(+), HESN and healthy donors.

METHODS

The neutrophils were stimulated with specific agonists for TLR2, TLR4 and TLR9 in the presence of HIV-1 particles. Pro-inflammatory cytokine production, expression of neutrophil activation markers and reactive oxygen species (ROS) production were analyzed in neutrophils from HESN, HIV-1(+) and healthy donors (controls).

RESULTS

We found that neutrophils from HESN presented reduced expression of PRR mRNAs (TLR4, TLR9, NOD1, NOD2, NLRC4 and RIG-I) and reduced expression of cytokine mRNAs (IL-1β, IL-6, IL-18, TNF-α and TGF-β). Moreover, neutrophils from HESN were less sensitive to stimulation through TLR4. Furthermore, neutrophils from HESN challenged with HIV-1 and stimulated with TLR2 and TLR4 agonists, produced significantly lower levels of reactive oxygen species, versus HIV-1(+).

CONCLUSIONS

A differential pattern of PRR expression and release of innate immune factors in neutrophils from HESN is evident. Our results suggest that lower neutrophil activation can be involved in protection against HIV-1 infection.

Specific loss of cellular L-selectin on CD4(+) T cells is associated with progressive multifocal leukoencephalopathy development during HIV infection

HIV(+) progressive multifocal leukoencephalopathy (PML) patients had a significantly lower expression of CD62L on CD4(+) T cells (P < 0.001) when compared with HIV(+) patients who did not develop PML. CD62L expression on CD4(+) T cells did not correlate with parameters such as CDC stage, CD4(+) cell percentage (of total CD3(+) T cells), CD4(+) cell counts, virus count, or clinical parameters. Measurement of CD62L might provide a biomarker for PML risk and could prompt a treatment change and/or close monitoring.

Soluble adhesion molecules as markers for sepsis and the potential pathophysiological discrepancy in neonates, children and adults

Sepsis is a severe and life-threatening systemic inflammatory response to infection that affects all populations and age groups. The pathophysiology of sepsis is associated with aberrant interaction between leukocytes and the vascular endothelium. As inflammation progresses, the adhesion molecules that mediate these interactions become shed from cell surfaces and accumulate in the blood as soluble isoforms that are being explored as potential prognostic disease biomarkers. We critically review the studies that have tested the predictive value of soluble adhesion molecules in sepsis pathophysiology with emphasis on age, as well as the underlying mechanisms and potential roles for inflammatory shedding. Five soluble adhesion molecules are associated with sepsis, specifically, E-selectin, L-selectin and P-selectin, intercellular adhesion molecule-1 and vascular cell adhesion molecule-1. While increased levels of these soluble adhesion molecules generally correlate well with the presence of sepsis, their degree of elevation is still poorly predictive of sepsis severity scores, outcome and mortality. Separate analyses of neonates, children and adults demonstrate significant age-dependent discrepancies in both basal and septic levels of circulating soluble adhesion molecules. Additionally, a range of both clinical and experimental studies suggests protective roles for adhesion molecule shedding that raise important questions about whether these should positively or negatively correlate with mortality. In conclusion, while predictive properties of soluble adhesion molecules have been researched intensively, their levels are still poorly predictive of sepsis outcome and mortality. We propose two novel directions for improving clinical utility of soluble adhesion molecules: the combined simultaneous analysis of levels of adhesion molecules and their sheddases; and taking age-related discrepancies into account. Further attention to these issues may provide better understanding of sepsis pathophysiology and increase the usefulness of soluble adhesion molecules as diagnostic and predictive biomarkers.

L-selectin and P-selectin are novel biomarkers of cervicovaginal inflammation for preclinical mucosal safety assessment of anti-HIV-1 microbicide

A major obstacle thwarting preclinical development of microbicides is the lack of a validated biomarker of cervicovaginal inflammation. Therefore, the present study aims to identify novel noninvasive soluble markers in a murine model for assessment of microbicide mucosal safety. By performing cytokine antibody array analysis, we identified two adhesion molecules, L-selectin and P-selectin, which significantly increased when mucosal inflammation was triggered by nonoxynol-9 (N9), an anti-HIV-1 microbicide candidate that failed clinical trials, in a refined murine model of agent-induced cervicovaginal inflammation. We found that patterns of detection of L-selectin and P-selectin were obviously different from those of the two previously defined biomarkers of cervicovaginal inflammation, monocyte chemotactic protein 1 (MCP-1) and interleukin 6 (IL-6). The levels of these two soluble selectins correlated better than those of MCP-1 and IL-6 with the duration and severity of mucosal inflammation triggered by N9 and two approved proinflammatory compounds, benzalkonium chloride (BZK) and sodium dodecyl sulfate (SDS), but not by two nonproinflammatory compounds, carboxymethyl celluose (CMC; microbicide excipients) and tenofovir (TFV; microbicide candidate). These data indicated that L-selectin and P-selectin can serve as additional novel cervicovaginal inflammation biomarkers for preclinical mucosal safety evaluation of candidate microbicides for the prevention of infection with HIV and other sexually transmitted pathogens.

Various viral compartments in HIV-1-infected mothers contribute to in utero transmission of HIV-1

Perinatal HIV transmission occurs in utero or intrapartum. The mechanisms and timing of transmission are not clearly understood. To compare the genetic sequences of the V3 envelope region of infant's plasma HIV to that of the mother's plasma, peripheral blood mononuclear cells (PBMC) and vaginal secretions, and correlate with timing of transmission. All 3 infants had a positive HIV PCR in the first days of life, thus classified as in utero infections. In the first mother-infant pair, two different variants were present in the infant, one correlating with maternal PBMC virus and highly homologous to virus from vaginal secretions and the other identical to sequences in maternal plasma. In the second pair, the infant plasma virus was similar to that of maternal PBMC. In the third pair, the cord blood and infant plasma virus were highly similar to maternal vaginal virus. The presence of more than one HIV variant from the maternal blood and from the vaginal compartment in the cord blood of infants presumably infected in utero could point to more than one episode of transmission or, alternatively, to transmission of PBMC virus.

Mother-to-child transmission of HIV: pathogenesis, mechanisms and pathways

More than 400,000 children were infected with (HIV-1) worldwide in 2008, or more than 1000 children per day. Mother-to-child transmission (MTCT) of HIV-1 is the most important mode of HIV acquisition in infants and children. MTCT of HIV-1 can occur in utero, intrapartum, and postnatally through breastfeeding. Great progress has been made in preventing such transmission, through the use of antiretroviral prophylactic regimens to the mother during gestation and labor and delivery and to either mother or infant during breast feeding. The timing and mechanisms of transmission, however, are multifactorial and remain incompletely understood. This article summarizes what is known about the pathogenetic mechanisms and routes of MTCT of HIV-1, and includes virologic, immunologic, genetic, and mucosal aspects of transmission.

Massive infection and loss of CD4+ T cells occurs in the intestinal tract of neonatal rhesus macaques in acute SIV infection

Rapid, profound, and selective depletion of memory CD4+ T cells has now been confirmed to occur in simian immunodeficiency virus (SIV)-infected adult macaques and human immunodeficiency virus (HIV)-infected humans. Within days of infection, marked depletion of memory CD4+ T cells occurs primarily in mucosal tissues, the major reservoir for memory CD4+ T cells in adults. However, HIV infection in neonates often results in higher viral loads and rapid disease progression, despite the paucity of memory CD4+ T cells in the peripheral blood. Here, we examined the immunophenotype of CD4+ T cells in normal and SIV-infected neonatal macaques to determine the distribution of naive and memory T-cell subsets in tissues. We demonstrate that, similar to adults, neonates have abundant memory CD4+ T cells in the intestinal tract and spleen and that these are selectively infected and depleted in primary SIV infection. Within 12 days of SIV infection, activated (CD69+), central memory (CD95+CD28+) CD4+ T cells are marked and persistently depleted in the intestine and other tissues of neonates compared with controls. The results in dicate that "activated" central memory CD4+ T cells are the major target for early SIV infection and CD4+ T cell depletion in neonatal macaques.

Mother-to-child transmission of HIV-1: timing and implications for prevention

This article provides a synthesis of clinical trial data with an aim to deduce the timing of mother-to-child transmission of HIV-1. Because transmission of the infection to the infant through breastfeeding is one of the main challenges in fighting paediatric HIV/AIDS in the developing world, we present separate estimates for the timing of HIV transmission for non-breastfeeding and breastfeeding populations. Our estimates predict that, for non-breastfeeding populations, 50% of HIV infections are transmitted to the infant at the very end of pregnancy, near to the time of labour. For breastfeeding populations, the postnatal period accounts for most of the HIV infections transmitted to the infant. We discuss the potential benefit of exclusive breastfeeding for the first 6 months of life as a policy to decrease the magnitude of HIV transmission. Furthermore, we present the hypothesis, based on recent research findings of viral latency, that the time when a fetus initially encounters the virus might not be when infection is established. We discuss the implications of this hypothesis and how it could lead to new interventions for the prevention of mother-to-child HIV transmission.

In vivo effects of HIV-1 exposure in the presence and absence of single-dose nevirapine on cellular plasma activation markers of infants born to HIV-1-seropositive mothers

Short-course antiretroviral drug regimens reduce the risk of mother-to-child transmission of HIV-1, but mechanisms affording protection of such interventions remain poorly defined. Because T-cell activation is an important factor in productive HIV-1 infection, we tested the hypothesis that single-dose nevirapine (NVP) reduces immune activation, which in turn reduces the likelihood of transmission. We compared concentrations of cord and maternal blood plasma immune activation markers, neopterin, beta2-microglobulin, and soluble l-selectin, in 2 groups of HIV-1-exposed newborns whose mothers either received NVP at the onset of labor or who only received NVP as postexposure prophylaxis within 72 hours of birth and among HIV-unexposed controls. In utero exposure of the infant to HIV-1, regardless of NVP exposure, led to demonstrable increases in immune activation markers, this being most notable in the presence of preexisting infection. Contrary to what was hypothesized, immune activation was increased by prebirth exposure to single-dose NVP, with this effect being enhanced in infants already infected at birth. Our data suggest that reductions in immune activation do not explain transmission prevention effects of single-dose NVP. Our data also suggest a biological explanation for why HIV-1-infected infants exposed perinatally to antiretroviral drugs might experience hastened disease progression, namely, in some HIV-1-infected individuals, NVP may synergize with HIV-1 to enhance an environment that favors increased HIV-1 replication.

Early virological events in various tissues of newborn monkeys after intrarectal infection with pathogenic simian human immunodeficiency virus

Children infected with human immunodeficiency virus type 1 often have higher viral loads and progress to acquired immunodeficiency syndrome more rapidly than adults. In our previous study of simian-human immunodeficiency virus (SHIV)-infected adult monkeys, immature CD4CD8 double-positive T cells in the thymus and jejunum decreased faster than mature CD4 single-positive T cells. Here, we examined the effect of virus replication on immature T cells from the same SHIV-inoculated newborn monkeys having more immature T cells than adults. The infectious viruses were more abundantly detected in the thymus than in other tissues at both 13 and 26 days post-infection (dpi). However, mature CD4(+) T cells in the thymus declined after 13 dpi and immature CD3(-) CD4 single-positive T cells remained at 26 dpi. These results suggested that many immature CD4(+) T cells in the thymus of newborns support the production of infectious viruses even after the depletion of mature CD4(+) T cells.

Soluble L-selectin, a marker of immune activation, in neonatal infection

L-Selectin is an adhesion molecule shed from the surface of lymphocytes and granulocytes upon activation. Soluble L-selectin in the plasma can thus reflect immune activation and is elevated in several pathological states. Our objective was to evaluate plasma levels of L-selectin as an immune activation marker in neonates and to determine whether it can serve as a marker of infection, either neonatal or congenital, or if it is affected by the mode of delivery and obstetrical or perinatal complications. A solid-phase ELISA was used on 89 sera from neonates less than 2 days of age, according to the manufacturer's instructions. Levels of soluble L-selectin in the neonate were lower than those of older infants and children and comparable to the levels seen in adults. There was no difference between levels of soluble L-selectin of premature (median, 1172 ng/ml) and full-term babies (median, 1151 ng/ml) or between babies born via vaginal (median, 1233 ng/ml) or cesarean delivery (median, 1146 ng/ml). Conditions such as preeclampsia or administration of steroids to the mother did not affect the levels of L-selectin in the neonate. In contrast, the presence of maternal clinical chorioamnionitis resulted in an increase in levels of L-selectin in the neonate (median, 1377 vs 1072 ng/ml, p = 0.02), as did neonatal sepsis (median, 1331 vs 1149 ng/ml, p = 0.026). Soluble L-selectin, and thus immune activation level, is highest in neonates with neonatal infection and needs to be further evaluated as a surrogate marker for diagnosing sepsis in the neonate.

Simian immunodeficiency virus infection in neonatal macaques

Children with human immunodeficiency virus infection often have higher viral loads and progress to AIDS more rapidly than adults. Since the intestinal tract is a major site of early viral replication and CD4(+) T-cell depletion in adults, we examined the effects of simian immunodeficiency virus (SIV) on both peripheral and intestinal lymphocytes from 13 neonatal macaques infected with SIVmac239. Normal neonates had more CD4(+) T cells and fewer CD8(+) T cells in all tissues than adults. Surprisingly, neonates had substantial percentages of CD4(+) T cells with an activated, memory phenotype (effector CD4(+) T cells) in the lamina propria of the intestine compared to peripheral lymphoid tissues, even when examined on the day of birth. Moreover, profound and selective depletion of jejunum lamina propria CD4(+) T cells occurred in neonatal macaques within 21 days of infection, which was preceded by large numbers of SIV-infected cells in this compartment. Furthermore, neonates with less CD4(+) T-cell depletion in tissues tended to have higher viral loads. The persistence of intestinal lamina propria CD4(+) T cells in some neonates with high viral loads suggests that increased turnover and/or resistance to CD4(+) T-cell loss may contribute to the higher viral loads and increased severity of disease in neonatal hosts.

Expression patterns of phenotypic markers on lymphocytes from human immunodeficiency virus type 2-infected baboons

The development of AIDS in HIV-1-infected humans is associated with profound changes in the expression patterns of lymphocyte phenotypic markers associated with increased immune activation and with decreased recall immune responses. In assessing these immunologic changes in an animal model, we characterized the expression patterns of immune activation markers on lymphocyte subsets during the acute, chronic, and end stages of HIV-2 infection in baboons. Using flow cytometry, we identified 21 human-specific monoclonal antibodies that were cross-reactive with baboon lymphocytes; however, expression of only 2 of these markers was altered significantly after HIV-2 infection. We found an increase in baboon class II antigen (as measured by anti-HLA-DR) in the CD4(+) T cell subset within 8 weeks of infection (p = 0.045). Moreover, after 1 year of infection, CD11b was downregulated on CD8(+) T lymphocytes (p = 0.027). This downregulation of CD11b was consistently observed in all of the groups of baboons that were chronically infected with three different HIV-2 isolates. In addition, we found substantial downregulation of the interleukin 2 receptor (CD25) and upregulation of class II antigen on CD8(+) lymphocytes in a baboon with an AIDS-like disease. These and other phenotypic markers of immune activation may facilitate characterization of the immunopathogenesis of AIDS in nonhuman primate animal models.

Human immunodeficiency virus (HIV)-specific cellular immune responses in newborns exposed to HIV in utero

Significant immunological changes are associated with intrauterine human immunodeficiency virus (HIV) encounter among uninfected infants of HIV-infected mothers. Peripheral blood cells of more than one-third of these exposed-uninfected infants proliferate and produce IL-2 after stimulation with HIV, and HIV-specific CD4+ T helper cell responses can be quantified in nearly all when sensitive intracellular cytokine assays are used. HIV-specific CD8+ cytotoxic T lymphocyte responses can be elicited in some, although less frequently. It is difficult to demonstrate that these responses are components of protective immunity and not simply epiphenomena of exposure. However, HIV-specific responses are associated with lack of infection, even with prolonged reexposure through breast-feeding. Elevations in nonspecific markers of immune activation provide further corroboration, as do similar findings in adults, consistent across all known routes of HIV transmission. Many questions remain, but much can be learned from this special population that may be informative for development of effective immunity in response to HIV vaccines.

Altered expression of L-selectin (CD62L) on polymorphonuclear neutrophils of children vertically infected with human immunodeficiency virus type 1

The expression of the leukocyte adhesion molecule L-selectin (CD62L) on polymorphonuclear neutrophils (PMN) and circulating levels of the soluble form of the receptor (sCD62L) were determined for a group of HIV-1-infected children, categorized as having mild or severe disease, and a group of uninfected control children. The fluorescence intensity of CD62L on PMN was significantly reduced in the HIV-1-infected children with mild disease compared to the uninfected controls. The proportion of lymphocytes expressing CD62L, as well as their corresponding fluorescence intensities, was significantly reduced in both the mild and the severe disease groups compared to the uninfected children, while peripheral levels of sCD62L were significantly elevated in the HIV-1-infected children with mild and severe disease compared to the controls. Altered cell migration resulting from reduced expression of CD62L may be an important contributor to the increased susceptibility to secondary microbial infections seen in HIV-1-infected children.