Human innate lymphoid cells (ILCs) in filarial infections.

Filarial infections are characteristically chronic and can cause debilitating diseases governed by parasite-induced innate and adaptive immune responses. Filarial parasites traverse or establish niches in the skin (migrating infective larvae), in nonmucosal tissues (adult parasite niche) and in the blood or skin (circulating microfilariae) where they intersect with the host immune response. While several studies have demonstrated that filarial parasites and their antigens can modulate myeloid cells (monocyte, macrophage and dendritic cell subsets), T- and B-lymphocytes and skin resident cell populations, the role of innate lymphoid cells during filarial infections has only recently emerged. Despite the identification and characterization of innate lymphoid cells (ILCs) in murine helminth infections, little is actually known about the role of human ILCs during parasitic infections. The focus of this review will be to highlight the composition of ILCs in the skin, lymphatics and blood; where the host-parasite interaction is well-defined and to examine the role of ILCs during filarial infections.

Dysregulation of interleukin 5 expression in familial eosinophilia.

BACKGROUND: Familial eosinophilia (FE) is a rare autosomal dominant inherited disorder characterized by the presence of lifelong peripheral eosinophilia (>1500/µL). Mapped to chromosome 5q31-q33, the genetic cause of FE is unknown, and prior studies have failed to demonstrate a primary abnormality in the eosinophil lineage. OBJECTIVE: The aim of this study was to identify the cells driving the eosinophilia in FE. METHODS: Microarray analysis and real-time PCR were used to examine transcriptional differences in peripheral blood mononuclear cells (PBMC), and in purified cell subsets from affected and unaffected family members belonging to a single large kindred. Cytokine levels in serum and PBMC culture supernatants were assessed by suspension array multiplexed immunoassays. RESULTS: Whereas IL-5 mRNA expression was significantly increased in freshly isolated PBMC from affected family members, this was not accompanied by increased mRNA expression of other Th2 cytokines (IL-4 or IL-13). Serum levels of IL-5 and IL-5 receptor α, but not IgE, were similarly increased in affected family members. Of note, IL-5 mRNA expression was significantly increased in purified CD3+ CD4+, CD14+, CD19+, and ILC2 cells from affected family members, as were IL-5 protein levels in supernatants from both stimulated PBMC and ILC2 cultures. CONCLUSIONS: These data are consistent with the hypothesis that the eosinophilia in FE is secondary to dysregulation of IL-5 production in PBMC (and their component subsets).

Looking beyond the induction of Th2 responses to explain immunomodulation by helminths.

Although helminth infections are characteristically associated with Th2-mediated responses that include the production of the prototypical cytokines IL-4, IL-5 and IL-13 by CD4(+) cells, the production of IgE, peripheral blood eosinophilia and mucus production in localized sites, these responses are largely attenuated when helminth infections become less acute. This modulation of the immune response that occurs with chronic helminth infection is often induced by molecules secreted by helminth parasites, by non-Th2 regulatory CD4(+) cells, and by nonclassical B cells, macrophages and dendritic cells. This review will focus on those parasite- and host-mediated mechanisms underlying the modulated T-cell response that occurs as the default in chronic helminth infections.

Brugia malayi infective larvae fail to activate Langerhans cells and dermal dendritic cells in human skin.

Filarial infection in humans is initiated when a mosquito deposits third-stage parasite larvae (L3) in the skin. Langerhans cells (LCs) and dermal dendritic cells (DDCs) are the first cells that the parasite encounters, and L3s must evade these highly effective antigen-presenting cells to establish infection. To assess LC and DDC responses to L3 in human skin, we employed three models of increasing physiologic relevance: in vitro-generated LCs, epidermal blister explants and full-thickness human skin sections. In vitro-generated LCs expressed TLR1-10 and robustly produced IL-6 and TNF-α in response to PolyI:C, but pre-exposure to L3s did not alter inflammatory cytokine production or TLR expression. L3s did not modulate expression of LC markers CDH1, CD207, or CD1a, or the regulatory products TSLP or IDO in epidermal explants or in vitro-generated LC. LC, CD14+ DDC, CD1c+ DC and CD141+ DC from human skin sections were analysed by flow cytometry. While PolyI:C potently induced CCL22 production in LC, CD1c+ DC, and CD141+ DC, and IL-10 production in LC, L3s did not modulate the numbers of or cytokine production by any skin DC subset. L3s broadly failed to activate or modulate LCs or DDCs, suggesting filarial larvae expertly evade APC detection in human skin.

Adaptation of innate lymphoid cells to a micronutrient deficiency promotes type 2 barrier immunity.

How the immune system adapts to malnutrition to sustain immunity at barrier surfaces, such as the intestine, remains unclear. Vitamin A deficiency is one of the most common micronutrient deficiencies and is associated with profound defects in adaptive immunity. Here, we found that type 3 innate lymphoid cells (ILC3s) are severely diminished in vitamin A-deficient settings, which results in compromised immunity to acute bacterial infection. However, vitamin A deprivation paradoxically resulted in dramatic expansion of interleukin-13 (IL-13)-producing ILC2s and resistance to nematode infection in mice, which revealed that ILCs are primary sensors of dietary stress. Further, these data indicate that, during malnutrition, a switch to innate type 2 immunity may represent a powerful adaptation of the immune system to promote host survival in the face of ongoing barrier challenges.

Immunology of lymphatic filariasis.

The immune responses to filarial parasites encompass a complex network of innate and adaptive cells whose interaction with the parasite underlies a spectrum of clinical manifestations. The predominant immunological feature of lymphatic filariasis is an antigen-specific Th2 response and an expansion of IL-10 producing CD4(+) T cells that is accompanied by a muted Th1 response. This antigen-specific T-cell hyporesponsiveness appears to be crucial for the maintenance of the sustained, long-standing infection often with high parasite densities. While the correlates of protective immunity to lymphatic filariasis are still incompletely understood, primarily due to the lack of suitable animal models to study susceptibility, it is clear that T cells and to a certain extent B cells are required for protective immunity. Host immune responses, especially CD4(+) T-cell responses clearly play a role in mediating pathological manifestations of LF, including lymphedema, hydrocele and elephantiasis. The main underlying defect in the development of clinical pathology appears to be a failure to induce T-cell hyporesponsiveness in the face of antigenic stimulation. Finally, another intriguing feature of filarial infections is their propensity to induce bystander effects on a variety of immune responses, including responses to vaccinations, allergens and to other infectious agents. The complexity of the immune response to filarial infection therefore provides an important gateway to understanding the regulation of immune responses to chronic infections, in general.

Filarial and Wolbachia genomics.

Filarial nematode parasites, the causative agents for a spectrum of acute and chronic diseases including lymphatic filariasis and river blindness, threaten the well-being and livelihood of hundreds of millions of people in the developing regions of the world. The 2007 publication on a draft assembly of the 95-Mb genome of the human filarial parasite Brugia malayi- representing the first helminth parasite genome to be sequenced - has been followed in rapid succession by projects that have resulted in the genome sequencing of six additional filarial species, seven nonfilarial nematode parasites of animals and nearly 30 plant parasitic and free-living species. Parallel to the genomic sequencing, transcriptomic and proteomic projects have facilitated genome annotation, expanded our understanding of stage-associated gene expression and provided a first look at the role of epigenetic regulation of filarial genomes through microRNAs. The expansion in filarial genomics will also provide a significant enrichment in our knowledge of the diversity and variability in the genomes of the endosymbiotic bacterium Wolbachia leading to a better understanding of the genetic principles that govern filarial-Wolbachia mutualism. The goal here is to provide an overview of the trends and advances in filarial and Wolbachia genomics.

CD2 identifies a monocyte subpopulation with immunoglobulin E-dependent, high-level expression of Fc epsilon RI.

BACKGROUND: Fc epsilon RI expression by monocytes can affect monocyte function via multiple mechanisms, thereby potentially influencing the generation of allergic inflammation. Previous studies on the in vivo regulation of monocyte Fc epsilon RI expression by ambient IgE have yielded conflicting results. OBJECTIVE: We hypothesized that monocyte Fc epsilon RI expression is limited to a specific monocyte subset, and that within that subset Fc epsilon RI surface expression is correlated to serum IgE. METHODS: Study 1: Blood was obtained from non-allergic subjects (n=14) and subjects with allergic asthma (n=18), hypereosinophilic syndrome (n=2), hyper-IgE syndrome (n=6), and helminth infection (n=4). Study 2: Blood was obtained from allergic subjects in a clinical trial of omalizumab before and during study drug treatment. Monocyte surface Fc epsilon RI expression was measured using flow cytometry. RESULTS: Fc epsilon RI expression was significantly greater in the CD2(high) vs. CD2(low) monocyte subsets (31% vs. 1.9% median Fc epsilon RI+, respectively). In asthmatic and non-atopic healthy control subjects, CD2(low) monocytes expressed little or undetectable Fc epsilon RI. In study 1, Fc epsilon RI expression was highly correlated to serum IgE in the CD2(high), but not in the CD2(low) monocyte subpopulation (R values of 0.67 and 0.41, respectively). In study 2, omalizumab, but not placebo, caused a significant and sustained decline in Fc epsilon RI expression within the CD2(high) monocyte subset. CONCLUSIONS: CD2 defines a monocyte subset with high Fc epsilon RI expression, whose magnitude is highly correlated to serum IgE. As such, this new description of CD2(high) monocytes as Fc epsilon RI-bearing cells suggests that they may be potential targets of anti-IgE immunomodulatory therapies.

Interdigital lesions and frequency of acute dermatolymphangioadenitis in lymphoedema in a filariasis-endemic area.

BACKGROUND: Lymphatic filariasis (LF) is a mosquito-borne nematode infection that causes permanent lymphatic dysfunction in virtually all infected individuals and clinical disease in a subset of these. One major sequel of infection is lymphoedema of the limbs. Lymphoedema of the leg affects an estimated 15 million persons in LF-endemic areas worldwide. Acute dermatolymphangioadenitis (ADLA) in people with filarial lymphoedema causes acute morbidity and increasingly severe lymphoedema. Episodes of ADLA are believed to be caused by bacteria, and it has been shown that entry lesions in the skin play a causative role. Clinical observations suggest that interdigital skin lesions of the feet, often assumed to be fungal, may be of particular importance. OBJECTIVES: To investigate the epidemiology and aetiology of interdigital lesions (IDL) of the feet in filarial lymphoedema. METHODS: The frequency and mycological aetiology of IDL in 73 patients with filarial lymphoedema were compared with 74 individuals without lymphoedema in a region of Guyana highly endemic for Wuchereria bancrofti. RESULTS: More than 50% of patients with lymphoedema had one or more IDL (odds ratio 2.69; 95% confidence interval 1.31-5.66; P<0.005 compared with controls). The number of lesions was the strongest predictor of frequency of ADLA. Only 18% of the lesions had positive microscopy or culture for fungi (dermatophytes and Scytalidium). CONCLUSIONS: These findings highlight the importance of interdigital entry lesions as risk factors for episodes of ADLA and have implications for the control of morbidity from filarial lymphoedema.

Diminished monocyte function in microfilaremic patients with lymphatic filariasis and its relationship to altered lymphoproliferative responses.

Antigen-specific hyporesponsiveness to filarial antigens is a phenomenon observed in patent infection with lymph-dwelling filarial parasites of humans. This phenomenon has been attributed to a multitude of factors, one of which is altered monocyte function. To examine the role played by monocytes in filarial infection, we assessed the responses of monocytes obtained from normal and filarial parasite-infected individuals to both crude filarial antigen and purified recombinant filarial antigen WbSXP-1 and attempted to relate these to the altered lymphoproliferative responses seen in filarial infection. Monocytes from microfilaremic (MF) patients demonstrated an inability to respond to lipopolysaccharide compared to monocytes from endemic normal persons or from lymphedema patients. Indeed, interleukin 1beta (IL-1beta) production was severely limited, a finding that did not extend to monocyte responses to filarial antigens. Serum from MF patients reduced adherence and spreading of normal monocytes, a finding not seen with serum from the other clinical groups. Interestingly, there was a significant correlation between the production of IL-1beta and adherence. Moreover, the levels of spontaneous production of IL-1beta correlated with high levels of spontaneous secretion of IL-10. The effects observed were not a result of diminished viability or alteration in the expression of the cell surface markers CD14 and HLA-DR. These data suggest that monocyte function is dampened in MF patients, a finding which could alter lymphoproliferative responses during patent infection.

Wuchereria bancrofti: cloning and characterization of heat shock protein 70 from the human lymphatic filarial parasite.

Heat shock protein 70 (HSP70) was identified as an immunodominant antigen by screening a Wuchereria bancrofti (Wb) microfilarial cDNA library with pooled Wb-infected sera, with 28% of the immunopositive clones coding for Wb-HSP70. The deduced amino acid sequence showed greater than 97 and 85% identity with HSP70 from filarial nematodes and humans, respectively. Recombinant HSP70 (74 kDa) and a recombinant protein from the C-terminal portion (43 kDa) also reacted with pooled Wb-infected sera, suggesting that the C-terminal region of HSP70 contains at least one antibody epitope. Brugia malayi L3 larvae showed increasing levels of HSP70 with increasing temperatures. Further, a polyclonal mouse anti-Wb-HSP70 antibody had reactivity to the HSP70 of cattle filarial parasite Settaria digitata and to human HSP70 derived from a Hep-2 cell line. Immune reactivity to Wb-HSP70 was strong, with uninfected non-endemic normal sera showing significantly greater reactions than sera from filaria-infected individuals. Both immunodominant self-HSP70 and HSP70 from other microbial infections may be primary targets for developing autoantibodies naturally.

Multicentre laboratory evaluation of Brugia Rapid dipstick test for detection of brugian filariasis.

A multicentre evaluation of the Brugia Rapid dipstick test was performed using 1263 serum samples in four international laboratories, i.e. T.D. Medical College (TDMC, India), National Institutes of Health (NIH, USA), Swiss Tropical Institute (STI, Switzerland) and Leiden University Medical Centre (LUMC, Netherlands). In comparison with microscopy, the dipstick demonstrated sensitivities of 97.2% (70 of 72) at TDMC, 91.6% (175 of 191) at LUMC and 100% (six of six) at STI. Sera of chronic patients showed a positivity rate of 11.3% (19 of 168) and 61.2% (71of 116) at TDMC and LUMC, respectively. All 266 sera of non-endemic normals from STI, NIH and LUMC tested negative with the dipstick. At LUMC, sera of 'endemic normals' (amicrofilaraemics with no clinical disease) from an area with approximately 35% microfilaria positivity showed 60.8% positive results (31 of 51), thus demonstrating the likelihood of many cryptic infections occurring in this population. Specificities of the test with Onchocerca volvulus sera were 98.8% (80 of 81) and 100% (10 of 10) at the NIH and STI, respectively; while specificity with Loa loa sera at the NIH was 84.6% (44 of 52). At the STI, the dipstick test also demonstrated 100% specificity when tested with 75 sera from various protozoan and helminthic infections.

Worm burden and host responsiveness in Wuchereria bancrofti infection: use of antigen detection to refine earlier assessments from the South Pacific.

A population from the Wuchereria bancrofti-endemic island of Mauke was reevaluated retrospectively by use of the Og4C3 circulating antigen (CAg) enzyme-linked immunosorbent assay to assess active infection in relation to host responses by age and gender. Use of microfilaremia (Mf) alone misclassified approximately 50% of infected people, although CAg and Mf levels were positively correlated. Levels of CAg peaked between those aged 31-60 years; men aged > 60 years had a significantly higher CAg prevalence (> 90%) than women. Filaria-specific immunoglobulin (Ig) G4 reached maximum levels in both genders at age 51-60 years. By analysis of variance, both age and gender significantly influenced CAg and IgG4, with men having higher levels of both in the total population. Individuals positive for CAg had significantly lower lymphocyte proliferation responses to parasite antigen than did CAg-negative people, regardless of clinical status. This study reemphasizes the importance of CAg measurements for accurately assessing filarial prevalence and clinical status and demonstrates the relationship between active infection and immune responsiveness.

Genetic polymorphisms in molecules of innate immunity and susceptibility to infection with Wuchereria bancrofti in South India.

A pilot study was conducted to determine if host genetic factors influence susceptibility and outcomes in human filariasis. Using the candidate gene approach, a well-characterized population in South India was studied using common polymorphisms in six genes (CHIT1, MPO, NRAMP, CYBA, NCF2, and MBL2). A total of 216 individuals from South India were genotyped; 67 normal (N), 63 asymptomatic microfilaria positive (MF+), 50 with chronic lymphatic dysfunction/elephantiasis (CP), and 36 tropical pulmonary eosinophilia (TPE). An association was observed between the HH variant CHIT1 genotype, which correlates with decreased activity and levels of chitotriosidase and susceptibility to filarial infection (MF+ and CP; P = 0.013). The heterozygosity of CHIT1 gene was over-represented in the normal individuals (P = 0.034). The XX genotype of the promoter region in MBL2 was associated with susceptibility to filariasis (P = 0.0093). Since analysis for MBL-sufficient vs insufficient haplotypes was not informative, it is possible the MBL2 promoter association results from linkage disequilibrium with neighboring loci. We have identified two polymorphisms, CHIT1 and MBL2 that are associated with susceptibility to human filarial infection, findings that merit further follow-up in a larger study.

Leishmaniasis recidivans recurrence after 43 years: a clinical and immunologic report after successful treatment.

We describe a patient with very late recurring leishmaniasis recidivans from whom lesional biopsy samples were obtained during and after topical steroid treatment that demonstrated the ability of the host to contain the parasite in the absence of therapy. Combination therapy with intralesional sodium stibogluconate and oral itraconazole was successful and immunologic data suggest that both CD4(+) and CD8(+) T cell subsets had roles in this disease process.

Filarial antigens impair the function of human dendritic cells during differentiation.

The antigen-specific T-cell unresponsiveness seen in lymphatic filariasis is mediated, in part, by diminished antigen-presenting cell function and is most specific for microfilariae (MF), the parasite stage found in large numbers in the peripheral circulation. We investigated the effect of MF antigen (MFAg) on dendritic cells (DC) in both their differentiation process from monocyte precursors and also after they have developed into DC. When MFAg was added to cultures of monocytes during their differentiation process to immature DC, the production of interleukin 12 (IL-12) p40, p70 protein, and IL-10 was significantly (P < 0.03) inhibited in response to Staphylococcus aureus Cowan (SAC) and SAC-gamma interferon (IFN-gamma) (60% to 80% inhibition). IL-10 was also inhibited (P = 0.04) in response to CD40 ligand-IFN-gamma. Moreover, MFAg inhibited the mRNA expression of IL-12 p40 and IL-10 as assessed by RNA protection assays. This effect was antigen specific, as another parasite antigen (soluble Toxoplasma gondii antigen) did not inhibit the production of these cytokines. This effect was also not a result of diminished cell viability nor of an alteration in surface expression of most costimulatory surface molecules, including major histocompatibility complex class I and class II. In contrast to exposure throughout the differentiation process, MFAg added to immature DC had no effect on DC cytokine expression. Although MF-differentiated DC were capable of inducing an allogeneic mixed lymphocyte reaction, they did so to a significantly lesser degree than DC without antigen exposure. These data collectively suggest that once DC are differentiated from their precursor cells, they become resistant to changes by MFAg.

Regulation of the immune response in lymphatic filariasis: perspectives on acute and chronic infection with Wuchereria bancrofti in South India.

Delineating the immune responses in lymphatic filariasis has been complicated not only by the rapidly expanding knowledge of new immunological mediators and effortors, but also by new methodologies (in particular, circulating filarial antigen detection) for defining and categorizing filarial-infected individuals. By using assays for circulating antigen in the sera collected as part of the many immunological studies performed on individuals in a Wuchereria bancrofti-endemic region of South India, we have attempted to explore the influence of patency on the antigen-driven proliferative and cytokine responses seen in peripheral blood mononuclear cells of individuals with varying clinical manifestations of lymphatic filarial infection. Moreover, we have provided perspectives on the differences between acute and chronic infection with W. bancrofti and suggested mechanisms that may underly the modulation of the immune response as patency occurs.

Early human infection with Onchocerca volvulus is associated with an enhanced parasite-specific cellular immune response.

The immune response after early exposure to or infection with Onchocerca volvulus was investigated in an autochthonous focus caused by the migration of infected persons to a previously unaffected area in Ecuador. Peripheral blood mononuclear cell (PBMC) proliferative and cytokine responses (interferon [IFN]-gamma and interleukin [IL]-5) to filarial antigens were measured in 14 subjects with serologic evidence of exposure and in 7 subjects with evidence of dermal microfilarial DNA and were compared with responses in 43 subjects with chronic O. volvulus infections. PBMC proliferative and cytokine responses (IFN-gamma and IL-5) to parasite antigens were elevated in the early exposure/infection group, compared with those in the chronic infection group. Addition of an IL-10-neutralizing antibody to filaria antigen-stimulated cultures resulted in significantly elevated proliferative responses in the chronic infection group. The findings suggest that early exposure and early parasite patency are associated with a vigorous cellular response, but, as infections become chronic, the cellular response becomes down-regulated, partly through an IL-10-dependent mechanism.

Human infection with Ascaris lumbricoides is associated with suppression of the interleukin-2 response to recombinant cholera toxin B subunit following vaccination with the live oral cholera vaccine CVD 103-HgR.

To investigate the potential immunomodulatory effects of concurrent ascariasis on the cytokine response to a live oral vaccine, we measured cytokine responses to cholera toxin B subunit (CT-B) following vaccination with the live oral cholera vaccine CVD 103-HgR in Ascaris lumbricoides-infected subjects randomized in a double-blind study to receive two doses of either albendazole or placebo prior to vaccination and in a group of healthy U.S. controls. Postvaccination cytokine responses to CT-B were characterized by transient increases in the production of interleukin-2 (IL-2; P = 0.02) and gamma interferon (IFN-gamma; P = 0.001) in the three study groups combined; however, postvaccination increases in IFN-gamma were significant only in the albendazole-treated A. lumbricoides infection group (P = 0.008). Postvaccination levels of IL-2 were significantly greater in the albendazole-treated group compared with the placebo group (P = 0.03). No changes in levels of Th1 and Th2 cytokines in response to control ascaris antigens were observed over the same period. These findings indicate that vaccination with CVD 103-HgR is associated with a Th1 cytokine response (IL-2 and IFN-gamma) to CT-B, that infection with A. lumbricoides diminishes the magnitude of this response, and that albendazole treatment prior to vaccination was able to partially reverse the deficit in IL-2. The potential modulation of the immune response to oral vaccines by geohelminth parasites has important implications for the design of vaccination campaigns in geohelminth-endemic areas.

Onchocerciasis in a nonendemic population: clinical and immunologic assessment before treatment and at the time of presumed cure.

Although suppressive therapy for onchocerciasis with intermittent ivermectin prevents the development of pathology in endemic populations, the clinical and immunologic effects of therapy in the absence of continued exposure are unknown. To address this question, 14 patients treated with ivermectin for onchocerciasis acquired >10 years ago during temporary residence in Africa were reevaluated. None had evidence of continued infection or pathology at follow-up. Although eosinophilia, serum IgE, and antifilarial antibody levels decreased after ivermectin therapy, none of these parameters was useful in predicting the resolution of symptoms in infected patients. Peripheral blood mononuclear cells isolated from patients at follow-up were more responsive to parasite antigen in vitro, which is as assessed by proliferation and production of interferon-gamma and interleukin (IL)-5. In contrast, antigen-induced levels of IL-10 were significantly decreased at follow-up, consistent with diminished down-regulatory factors rather than a switch from type 2 to type 1 immune responses.