Increased IFN-γ production by NK and CD3+/CD56+ cells in sexually HIV-1-exposed but uninfected individuals

Specific phenotypic and functional features of natural killer cells from HIV-infected long-term nonprogressors and HIV controllers

BACKGROUND

Recent evidence suggests that natural killer (NK) cells play a crucial role in the HIV pathogenesis. Long-term nonprogressor (LTNP) and HIV controllers are rare HIV-infected patients who control viral replication and show delayed disease progression. They represent fascinating models of natural protection against disease progression and for studying the immunological response to the virus.

METHODS

We have conducted an extensive analysis of the phenotypic and functional properties of CD56, CD56 and CD56/CD16 NK cell subsets from LTNP and HIV-controllers, and compared them with HIV progressors and healthy donors.

RESULTS

Hierarchical clustering analysis of NK phenotypic markers revealed that LTNP and HIV controllers, exhibit peculiar phenotypic features, associated with high levels of interferon-g, activation markers, and cytolytic activity in CD3CD56 NK cells against K562 target cells. More importantly, cytolytic activity against autologous CD4 T cells is abrogated after treatment with anti-NKp44L mAb, in LTNP and HIV progressors, suggesting a key role of NKp44L. In contrast, in HIV controllers and healthy donors, NKp44L expression on CD4 T cells and autologous NK lysis were both poorly detected.

CONCLUSIONS

These results show that NK cells from LTNP and HIV controllers display phenotypic and functional features and suggest a consistent continuous involvement of the innate immune response in the failure to control viral replication. Collectively, these data may have important implication in the design of new anti-HIV therapeutical strategies based on the particular functional activity of NK cells.

Cytokine secretion is distinct from secretion of cytotoxic granules in NK cells

NK cells are renowned for their ability to kill virally infected or transformed host cells by release of cytotoxic granules containing granzymes and perforin. NK cells also have important regulatory capabilities chiefly mediated by secretion of cytokines, such as IFN-gamma and TNF. The secretory pathway for the release of cytokines in NK cells is unknown. In this study, we show localization and trafficking of IFN-gamma and TNF in human NK cells in compartments and vesicles that do not overlap with perforin or other late endosome granule markers. Cytokines in post-Golgi compartments colocalized with markers of the recycling endosome (RE). REs are functionally required for cytokine release because inactivation of REs or mutation of RE-associated proteins Rab11 and vesicle-associated membrane protein-3 blocked cytokine surface delivery and release. In contrast, REs are not needed for release of perforin from preformed granules but may be involved at earlier stages of granule maturation. These findings suggest a new role for REs in orchestrating secretion in NK cells. We show that the cytokines IFN-gamma and TNF are trafficked and secreted via a different pathway than perforin. Although perforin granules are released in a polarized fashion at lytic synapses, distinct carriers transport both IFN-gamma and TNF to points all over the cell surface, including within the synapse, for nonpolarized release.

TLR activation pathways in HIV-1-exposed seronegative individuals

TLRs trigger innate immunity that recognizes conserved motifs of invading pathogens, resulting in cellular activation and release of inflammatory factors. The influence of TLR activation on resistance to HIV-1 infection has not been investigated in HIV-1 exposed seronegative (ESN) individuals. PBMCs isolated from heterosexually ESN individuals were stimulated with agonists specific for TLR3 (poly I:C), TLR4 (LPS), TLR7 (imiquimod), and TLR7/8 (ssRNA40). We evaluated expression of factors involved in TLR signaling cascades, production of downstream effector immune mediators, and TLR-expression in CD4+ and CD14+ cells. Results were compared with those obtained in healthy controls (HCs). ESN individuals showed: 1) comparable percentages of CD14+/TLR4+ and CD4+/TLR8+ CD14+/TLR8+ cells; 2) higher responsiveness to poly I:C, LPS, imiquimod, and ssRNA40 stimulation, associated with significantly increased production of IL-1beta, IL-6, TNF-alpha, and CCL3; 3) augmented expression of mRNA specific for other targets (CCL2, CSF3, CSF2, IL-1alpha, IL-8, IL-10, IL-12, cyclooxygenase 2) demonstrated by broader TLRs pathway expression analyses; and 4) increased MyD88/MyD88s(short) ratio, mainly following TLR7/8 stimulation. We also compared TLR-agonist-stimulated cytokine/chemokine production in CD14+ PBMCs and observed decreased IFN-beta production in ESN individuals compared with HCs upon TLR7/8-agonist stimulation. These data suggest that TLR stimulation in ESN individuals results in a more robust release of immunologic factors that can influence the induction of stronger adaptive antiviral immune responses and might represent a virus-exposure-induced innate immune protective phenotype against HIV-1.

Innate immune responses in primary HIV-1 infection

PURPOSE OF REVIEW

Events occurring in acute HIV-1 infection are now recognized to be critical determinants of the subsequent disease course. Innate responses constitute the first line of defence against pathogens, and also play a key role in triggering the early adaptive response; as such, the innate responses activated in acute HIV-1 infection and their contribution to control of viral replication or disease pathogenesis are the focus of much current research. We review recent advances in this area.

RECENT FINDINGS

Dendritic cell subsets can play pleiotropic roles in acute HIV-1 infection, with in-vitro studies illustrating that HIV-dendritic cell interactions may have outcomes as diverse as virion destruction, virus dissemination, T-cell triggering or subversion of dendritic cell functions. Natural killer cells can be activated in acute HIV-1 infection, and mounting evidence suggests that they contribute to determining the ensuing course of disease; however, much remains to be learned about how they mediate their effects.

SUMMARY

The importance of innate responses as determinants of the outcome of HIV infection is increasingly evident, but more work is needed to understand how innate immunity can be harnessed to combat this infection.

Sexual transmission of HIV-1

HIV-1 transmission occurs in a limited number of ways all of which are preventable. Overall, the risk of HIV-1 transmission following a single sexual exposure is low especially in comparison with other sexually transmitted infections (STIs); with estimates of the average probability of male to female HIV-1 transmission only 0.0005-0.0026 per coital act. The risk of acquiring HIV-1 from a single contact varies enormously and is dependant upon the infectiousness of the HIV-1 positive individual and the susceptibility to HIV-1 of their sexual partner. An understanding of the determinants of HIV-1 transmission is important not only to assess the infection risk to an individual when exposed to the virus (e.g. to determine the provision of post exposure prophylaxis), but also to make accurate predictions on the potential spread of HIV-1 infection in a population and to direct appropriate targeted prevention strategies. In this review article we summarise the current literature on the major worldwide source of HIV-1 acquisition, sexual transmission. This article forms part of a special issue of Antiviral Research marking the 25th anniversary of antiretroviral drug discovery and development, Vol 85, issue 1, 2010.

Human uterine natural killer cells but not blood natural killer cells inhibit human immunodeficiency virus type 1 infection by secretion of CXCL12

Natural killer (NK) cells derived from the human female reproductive tract (FRT) are phenotypically and functionally distinct from those obtained from peripheral blood. Because the FRT is a primary site of human immunodeficiency virus type 1 (HIV-1) infection in women, we determined whether soluble factors secreted by uterine-derived NK (uNK) cells inhibit HIV-1 infection. Clonal populations of uNK cells were activated with interleukin-12 (IL-12) and IL-15, and conditioned media (CM) from these cultures evaluated for their ability to inhibit infection of cells by HIV-1(IIIB), HIV-1(NL4.3), and HIV-1(HC4) (X4-tropic) or HIV-1(BaL) (R5-tropic) viruses. We found that soluble factors secreted by activated uNK cells significantly inhibited X4-tropic virus infection of TZM-bl cells, peripheral blood mononuclear cells, and primary human endometrial cells, but not infection by HIV-1(BaL). In contrast, CM from peripheral blood NK (bNK) cells did not inhibit HIV-1 infection of cells. Analysis of factors secreted from uNK clones with anti-HIV-1 activity demonstrated significantly higher levels of CXCL12 compared to uNK clones without this activity, and the HIV inhibitory activity was neutralized by antibodies to CXCL12. Collectively, these data demonstrate that human uNK cells release chemokines with anti-HIV-1 activity for X4-tropic strains and this suggest that these chemokines may contribute to the inhibition of X4-tropic strain transmission across mucosal tissues.

Cutting Edge: Unusual NK cell responses to HIV-1 peptides are associated with protection against maternal-infant transmission of HIV-1

Most infants exposed to HIV-1 in utero and at delivery do not acquire infection. We show that mothers and infants who have CD3-negative cells that respond to HIV-1 peptides are substantially less likely to transmit and acquire infection, respectively. The CD3-negative cells, shown to be NK cells, respond with remarkable specificity and high magnitude to HIV-1 peptides from Env (envelope) and Reg (regulatory) protein regions, as measured by a whole blood intracellular cytokine assay only in the context of HIV-1 infection or exposure. These findings identify an important new measure of protective immunity to HIV-1 that highlights the importance of innate immunity in preventing the establishment of HIV-1 infection.

Imbalance of naive and memory T lymphocytes with sustained high cellular activation during the first year of life from uninfected children born to HIV-1-infected mothers on HAART

The immune consequences of in utero HIV exposure to uninfected children whose mothers were submitted to highly active antiretroviral therapy (HAART) during gestation are not well defined. We evaluated 45 HIV-exposed uninfected (ENI) neonates and 45 healthy unexposed control (CT) neonates. All HIV-infected mothers received HAART during pregnancy, and the viral load at delivery was <50 copies/mL for 56.8%. Twenty-three ENI neonates were further evaluated after 12 months and compared to 23 unexposed healthy age-matched infants. Immunophenotyping was performed by flow cytometry in cord and peripheral blood. Cord blood lymphocyte numbers did not differ between groups. However, ENI neonates had a lower percentage of naive T cells than CT neonates (CD4+, 76.6 vs 83.1%, P < 0.001; CD8+, 70.9 vs 79.6%, P = 0.003) and higher percentages of central memory T cells than CT neonates (CD4+, 13.9 vs 8.7%, P < 0.001; CD8+, 8.6 vs 4.8%, P = 0.001). CD38 mean fluorescence intensity of T cells was higher in ENI neonates (CD4+, 62.2 vs 52.1, P = 0.007; CD8+, 47.7 vs 35.3, P < 0.001). At 12 months, ENI infants still had higher mean fluorescence intensity of CD38 on T cells (CD4+, 34.2 vs 23.3, P < 0.001; CD8+, 26.8 vs 19.4, P = 0.035). Despite effective maternal virologic control at delivery, HIV-exposed uninfected children were born with lower levels of naive T cells. Immune activation was present at birth and remained until at least 12 months of age, suggesting that in utero exposure to HIV causes subtle immune abnormalities.

Increased levels of human beta-defensins mRNA in sexually HIV-1 exposed but uninfected individuals

Protection against HIV-1 infection in exposed seronegative (ESN) individuals likely involves natural resistance mechanisms that have not been fully elucidated. Human beta defensins (HBD) are antimicrobial peptides found primarily in mucosae, the main ports of HIV entry. HBD-2 and 3 mRNA are induced by HIV-1 in human oral epithelial cells and exhibit strong anti-HIV-1 activity; in addition, polymorphisms in the DEFB1 gene, which encodes HBD-1, have been associated with resistance/susceptibility to different infections, including HIV-1. Here, we have assessed the association of HBD expression with the ESN phenotype. Peripheral blood and vaginal/endocervical and oral mucosal samples were taken from 47 ESN, 44 seropositive (SP) and 39 healthy controls (HC). HBD-1, 2 and 3 mRNA copy numbers were quantified by real time RT-PCR and A692G/G1654A/A1836G polymorphisms in the DEFB1 gene were detected by restriction fragment length polymorphisms and confirmed by nucleotide sequencing. ESN expressed significantly greater mRNA copy numbers of HBD-2 and 3 in oral mucosa than HC; p=0.0002 and p=0.007, respectively. mRNA copy numbers of HBD-1, 2 and 3 in vaginal/endocervical mucosa from ESN and HC were similar. Homozygosity for the A692G polymorphism was significantly more frequent in ESN (0.39) than in SP (0.05) (p=0.0002). In summary, ESN exhibited enhanced mucosal expression of the innate defense genes HBD-2 and 3; however, additional studies are required to verify these results and the potential association of the A692G polymorphism to the relative resistance of ESN to HIV-1 infection.

Potentially exposed but uninfected individuals produce cytotoxic and polyfunctional human immunodeficiency virus type 1-specific CD8(+) T-cell responses which can be defined to the epitope level

We measured CD8(+) T-cell responses in 12 potentially exposed but uninfected men who have sex with men by using cytokine flow cytometry. Four of the individuals screened exhibited polyfunctional immune responses to human immunodeficiency virus type 1 Gag or Vif. The minimum cytotoxic T lymphocyte epitope was mapped in one Gag responder.

IL-21 augments natural killer effector functions in chronically HIV-infected individuals

OBJECTIVE

This study addresses the interleukin (IL)-21 effects on resting peripheral blood natural killer (NK) cells in chronically HIV-infected individuals.

DESIGN

The effects of IL-21 on perforin expression, proliferation, degranulation, interferon (IFN)-gamma production, cytotoxicity and induction of STAT phosphorylation in NK cells were determined in vitro.

METHODS

Peripheral blood mononuclear cells from HIV-infected and healthy individuals were incubated in vitro for 6 h, 24 h or 5 days with IL-21 or IL-15. Percentages of perforin, IFN-gamma, CD107a, NKG2D and STAT3-5 positive cells were determined within NK cell populations. K562 cells were used as target cells in NK cytotoxicity assay.

RESULTS

Frequency of CD56 cells in chronically HIV-infected individuals was diminished. Perforin expression in CD56 and CD56 was comparable in healthy and HIV-infected individuals. IL-15 upregulated perforin expression primarily in CD56 NK cells, whereas IL-21 upregulated perforin in both NK subsets. IL-21 and IL-15 upregulated CD107a and IFN-gamma, as well as NK cytotoxicity. IL-15 predominantly activated STAT5, whereas IL-21 activated STAT5 and STAT3. IL-15, but not IL-21 increased NK cell proliferation in uninfected and HIV-infected individuals.

CONCLUSION

IL-21 augments NK effector functions in chronically HIV-infected individuals and due to its perforin enhancing properties it has potential for immunotherapy or as a vaccine adjuvant.

A combined genotype of KIR3DL1 high expressing alleles and HLA-B*57 is associated with a reduced risk of HIV infection

OBJECTIVES

Coexpression of certain combinations of natural killer cell receptor KIR3DL1 and HLA-B alleles is associated with slower time to AIDS. The strongest protection in terms of disease outcome in KIR3DL1 homozygotes (3DL1 hmz) is coexpression of HLA-B*57 and a set of KIR3DL1 genotypes (3DL1*h/*y) lacking alleles expressed at low levels on natural killer cells. We questioned whether this allele combination could also influence resistance to infection.

DESIGN

The genetic distribution of 3DL1*h/*y and HLA-B*57 was compared in 41 HIV-exposed uninfected and 186 recently HIV-infected 3DL1 hmz.

METHODS

KIR3DL1 subtyping was performed by sequencing the exons 3, 4, 5, 7-9. The major histocompatibility complex class IB locus was typed by sequence specific oligonucleotide PCR and sequencing to resolve Bw4 and Bw6 alleles and the amino acid present at position 80.

RESULTS

Percentage carriers of HLA-B*57 in HIV-exposed uninfected and individuals in a primary infection cohort was 12.2 and 4.3%, respectively (P = 0.0631), whereas that of 3DL1*h/*y was similar in both populations (P = 0.221). The 3DL1*h/*y-HLA-B*57 combined genotype was more frequent in exposed uninfected individuals (12.2%) than individuals in primary infection (2.7%) (P = 0.019; odds ratio, 5.03; 95% confidence intervals, 1.38-18.3).

CONCLUSION

Coexpression of 3DL1*h/*y and B*57, which has been associated with a reduced risk of progressing to AIDS in HIV-infected individuals also lowers the risk of HIV infection in exposed uninfected individuals.

Activation of interferon response genes and of plasmacytoid dendritic cells in HIV-1 positive subjects with GB virus C co-infection

GB virus C (GBV-C) coinfection has a protective role in Human Immunodeficiency Virus (HIV) infection, and increases the duration of suppression of HIV-1 viremia in patients under Highly Active Anti-Retroviral Therapy (HAART). Since innate antiviral response may be involved in the protection, we analyzed the possible role of GBV-C as activator of innate immunity. To this aim, we measured the extent of activation of the interferon (IFN) system and of circulating Dendritic Cells (DC) in vivo, and the ability of GBV-C to activate these functions in vitro. Activation of IFN system and of circulating DC was compared in GBV-positive and -negative HIV-1 co-infected patients with HAART-driven suppression of HIV-1 viremia. Endogenous levels of IFN-gamma and RNA-dependent protein kinase (PKR) mRNA were significantly higher in peripheral blood mononuclear cells (PBMC) from GBV-C-positive when compared to GBV-C-negative patients. IFN-gamma expression was correlated with all the Interferon response genes (IRGs) and with GBV-C viremia. The frequency of circulating plasmacytoid DC (pDC) expressing the CD80 activation marker was increased in GBV-C-positive patients, and was correlated with GBV-C viral load. In vitro experiments indicated that GBV-C is able to induce IFN-gamma expression in PBMC. In addition, in PBMC cultures GBV-C induced an increase of CD80 expression by pDC, that was reduced by antibody to IFN-gamma. Our data indicate that in HIV-positive patients GBV-C coinfection promotes the activation of IFN-gamma and downstream IRG expression, as well as with the activation/maturation of circulating pDC. GBV-C-driven IFN-gamma activation is, at least in part, responsible for the increased maturation of pDC. This crosstalk may suggest a role for GBV-C coinfection in boosting the innate antiviral response to HIV infection.

Infection with Vpr-positive human immunodeficiency virus type 1 impairs NK cell function indirectly through cytokine dysregulation of infected target cells

Human immunodeficiency virus type 1 (HIV-1) infection has been implicated in impairing various aspects of NK cell function in viremic condition, and several viral factors contribute to these defects. Here, we evaluated the effect of HIV-1 Vpr on NK cell cytolytic function and cytokine (gamma interferon [IFN-gamma]) production in the context of infection and exposure. Our data indicate that NK cells derived from a peripheral blood mononuclear cell culture infected in vitro with HIV-1 vpr(+) virus or exposed to recombinant Vpr protein exhibited reduced target cell killing in conjunction with diminished expression of CD107a and reduced IFN-gamma production compared to their Vpr-negative counterparts. This Vpr-induced NK cell defect is in part through differential regulation of interleukin-12 and transforming growth factor beta production by the infected target cells and concomitant activation of Smad3 signaling pathway. Collectively, these results illustrate the ability of Vpr to impair NK cell-mediated innate immune functions indirectly by dysregulating multiple cytokines in the infected target cells, thus increasing disease severity and affecting the final outcome in HIV-1 infection.

Increased proportion of KIR3DS1 homozygotes in HIV-exposed uninfected individuals

OBJECTIVES

Natural killer (NK) cell activity is increased in individuals who remain uninfected despite repeated exposures to HIV. Given that a combined major histocompatibility complex (MHC) class I and killer immunoglobulin-like receptor (KIR) KIR3D genotype has been linked to rate of HIV disease progression, we assessed whether these genotypes played a role in protection from infection.

DESIGN

The study genotyped 80 HIV-exposed uninfected (EU) and 304 subjects in HIV primary infection (PI) at the MHC class IB and KIR3DS/L1 loci.

METHODS

KIR3D genotyping was performed by sequence-specific primer polymerase chain reaction using two pairs of specific primers for each locus. The MHC class IB locus was typed by sequence-specific oligonucleotide polymerase chain reaction and sequencing to resolve Bw4 and Bw6 alleles and the amino acid present at position 80.

RESULTS

Comparison of the genetic distribution of KIR3D, HLA Bw4 and HLA Bw4-I80 genotypes in EU versus PI subjects reveal an increased proportion of KIR3DS1 homozygotes in EU (11/80, 13.8%) compared to subjects in PI (16/304, 5.3%). Analyses of combined MHC class I and KIR3D expression show no differences between the two populations.

CONCLUSIONS

Homozygosity for the activating NK receptor KIR3DS1, may contribute to the more active NK cell function observed in EU and their relative resistance to HIV infection.

Conferral of enhanced natural killer cell function by KIR3DS1 in early human immunodeficiency virus type 1 infection

A flurry of recent reports on the role of activating and inhibitory forms of the killer cell immunoglobulin-like receptors (KIR) in natural killer (NK) cell activity against human immunodeficiency virus type 1 (HIV-1) have yielded widely divergent results. The role of the activating NK receptor encoded by the KIR3DS1 allele and its putative ligands, members of the HLA class I Bw4Ile80 cluster, in early HIV-1 disease is controversial. We selected 60 treatment-naïve adults for study from the OPTIONS cohort of individuals with early HIV-1 infection in San Francisco. We performed NK cell functional assays measuring gamma interferon (IFN-gamma) and CD107a expression by NK cells in the unstimulated state and after stimulation by the major histocompatibility complex class I-deficient 721.221 B-lymphoblastoid cell line. In addition, we measured CD38 expression (a T-cell activation marker) on T and NK cells. Persons who have at least one copy of the KIR3DS1 gene had higher IFN-gamma and CD107a expression in the unstimulated state compared to those who do not possess this gene. After stimulation, both groups experienced a large induction of IFN-gamma and CD107a, with KIR3DS1 carriers achieving a greater amount of IFN-gamma expression. Differences in effector activity correlating with KIR3DS1 were not attributable to joint carriage of HLA Bw4Ile80 and KIR3DS1. We detected a partial but not complete dependence of KIR3DS1 on the members of B*58 supertype (B*57 and B*58) leading to higher NK cell function. Possessing KIR3DS1 was associated with lower expression of CD38 on both CD8(+) T and NK cells and with a loss or weakening of the known strong associations between CD8(+) T-cell expression of CD38 mean fluorescence intensity and the HIV-1 viral load. We observed that possessing KIR3DS1 was associated with higher NK cell effector functions in early HIV-1 disease, despite the absence of HLA Bw4Ile80, a putative ligand of KIR3DS1. Carriage of KIR3DS1 was associated with diminished CD8(+) T-cell activation, as determined by expression of CD38, and a disruption of the traditional relationship between viral load and activation in HIV-1 disease, which may lead to better clinical outcomes for these individuals.

Effect of intrauterine HIV-1 exposure on the frequency and function of uninfected newborns' dendritic cells

Immaturity of the neonatal immune system is considered an underlying factor for enhanced severity of infections in newborns. Functional defects of neonatal antigen-presenting cells lead to defective T-cell responses. T cells from uninfected neonates exposed in utero to HIV-1 (EU) exhibit phenotypic and functional alterations; however, the function of their circulating dendritic cells (DCs) has not been characterized. We hypothesized that an HIV-1-infected maternal environment may influence the infants' DC number, phenotype and function. EU exhibited a higher percentage of myeloid DCs (mDCs) than unexposed neonates, although this frequency remained lower than that observed in adults. Plasmacytoid DC (pDC) frequencies were similar in all groups, although both groups of infants tended to have lower frequencies than adults. After LPS stimulation, mDCs from EU up-regulated CD80, CD86 and B7-H1, whereas mDCs from unexposed infants upregulated B7-H1, but not CD80/CD86, and adult mDCs up-regulated mainly CD80 and CD86. IFN-alpha production was similar in all groups, indicating a normal pDC function. Therefore, in utero exposure to HIV-1 induces quantitative and qualitative changes in neonatal DCs, particularly in mDCs, which might be associated with alterations observed in T cells from these EU.

Natural Killer cells from long-term non-progressor HIV patients are characterized by altered phenotype and function

Natural killer (NK) cells are part of the innate immune system important in the control of viral infections and recent evidence suggests that they may play a role in the pathogenesis of HIV. Long-term non-progressor (LTNP) HIV patients who control replication of the virus and show a delayed disease progression have naturally occurring successful immune responses to HIV. We investigated a role for NK cells in these patients. In agreement with previous reports, NK cell cytotoxic activity was decreased in viremic HIV patients relative to healthy individuals (p<0.05). Viremic HIV patients showed an altered cell surface phenotype, including a reduction in natural cytotoxicity receptor expression and an increase in leukocyte immunoglobulin-like receptor subfamily B member 1 (LILRB1) expression. These phenotypic changes were also present in LTNP patients; however, these patients showed increased levels of NK cell activity relative to viremic HIV patient group.

Mucosal immune responses in the genital tract of HIV-1-exposed uninfected women

The development of HIV-1 vaccines and microbicides remains hindered by our limited understanding of correlates of immune protection to infection. Evidence indicating that resistance to HIV-1 infection is indeed possible comes from HIV-1-exposed yet uninfected individuals, including cohorts of commercial sex workers and discordant couples. Despite their uninfected status some of these individuals have mucosal and systemic HIV-1-specific humoral and cellular immune responses in addition to their innate immune response. The combined contribution of innate and adaptive immunity as well as genetic factors is most likely of great importance for this protection against infection. Here we review data on the antibody responses and secreted immune molecules of the innate immune system in the female genital tract with emphasis on individuals who seem to resist HIV-1-infection despite repeated exposure to the virus.

Distinctive NK-cell receptor repertoires sustain high-level constitutive NK-cell activation in HIV-exposed uninfected individuals

We have previously associated high natural killer (NK)–cell activity and protection against HIV-1 infection in Vietnamese exposed uninfected intravascular drug users (EUs). Considering that activating and inhibitory signals sensed by NK-cell receptors regulate NK-cell activation, we performed phenotypic and quantitative reverse transcription-polymerase chain reaction (qRT-PCR) transcript analyses of the NK-cell receptor (NKR) repertoire in 25 EUs, 19 HIV+ intravenous drug users, and 26 uninfected blood donors. Although NK-cell activation was not linked to a unique NKR repertoire in EUs, various patterns consistent with NK-cell activation were detected in EUs: high KIR3DS1/KIR3DL1 ratio associated with down-regulated KIR3DL1 transcript levels, KIR2DL3+ low-affinity receptor expansion associated to group HLA-C1 ligand in 2DS2−/2DL2− EUs, enhanced NKG2C/NKG2A ratio, and increased CD69 expression. Remarkably, EUs exhibited high constitutive degranulation activity in the absence of exogenous stimulation, as shown by the CD107a assay. Furthermore, CD161 expression was increased within the CD107a+ NK-cell compartment. Our results suggest that in response to viral exposition, particular genetic or regulated features of the NKR repertoire of EUs contribute to their high constitutive NK-cell potential. This might allow NK cells to generate a more rapid and effective immune response to HIV-1, thereby contributing to prevention toward infection.

Innate immune defenses in HIV-1 infection: prospects for a novel immune therapy

HIV-1 infection leads to a severe decrease of CD4(+) T lymphocytes, dysregulation of several leukocyte subpopulations and generalized immune activation, with the subsequent development of opportunistic infections and malignancies. Administration of highly active antiretroviral therapy (HAART) has been successful in reducing HIV-1 plasma viremia; however, the ability of HAART to restore immunocompetence appears incomplete, particularly in patients with chronic and advanced disease. Several components of the innate immune system have direct anti-HIV-1 effects, and studies to analyze the benefits of enhancing the function of the innate response during HIV-1 infection are increasing. Development of any complementary therapeutic approaches to HIV-1 infection, particularly those able to compensate for the limitations of HAART, and enhance the anti-HIV-1 innate immune activity would be of interest. The stimulation of innate immune responses using Toll-like receptor agonists, such as monophosphoryl lipid A and oligodeoxynucleotides with CpG motifs, are currently being investigated and their benefit in HIV-1-infected patients are under evaluation.

IL-22 participates in an innate anti-HIV-1 host-resistance network through acute-phase protein induction

Certain individuals are resistant to HIV-1 infection, despite repeated exposure to the virus. Although protection against HIV-1 infection in a small proportion of Caucasian individuals is associated with mutant alleles of the CCR5 HIV-1 coreceptor, the molecular mechanism underlying resistance in repeatedly HIV-1-exposed, uninfected individuals (EU) is unclear. In this study, we performed complementary transcriptome and proteome analyses on peripheral blood T cells, and plasma or serum from EU, their HIV-1-infected sexual partners, and healthy controls, all expressing wild-type CCR5. We report that activated T cells from EU overproduce several proteins involved in the innate immunity response, principally those including high levels of peroxiredoxin II, a NK-enhancing factor possessing strong anti-HIV activity, and IL-22, a cytokine involved in the production of acute-phase proteins such as the acute-phase serum amyloid A (A-SAA). Cell supernatants and serum levels of these proteins were up-regulated in EU. Moreover, a specific biomarker for EU detected in plasma was identified as an 8.6-kDa A-SAA cleavage product. Incubation of in vitro-generated myeloid immature dendritic cells with A-SAA resulted in CCR5 phosphorylation, down-regulation of CCR5 expression, and strongly decreased susceptibility of these cells to in vitro infection with a primary HIV-1 isolate. Taken together, these results suggest new correlates of EU protection and identify a cascade involving IL-22 and the acute phase protein pathway that is associated with innate host resistance to HIV infection.