The immune response to a meningococcal polysaccharide vaccine in an African village

Asymptomatic Malaria Infection and the Immune Response to the 2-Dose Ad26.ZEBOV, MVA-BN-Filo Ebola Vaccine Regimen in Adults and Children

Background

Malaria infection affects the immune response to some vaccines. As Ebola virus (EBOV) outbreaks have occurred mainly in malaria-endemic countries, we have assessed whether asymptomatic malaria affects immune responses to the 2-dose Ad26.ZEBOV, MVA-BN-Filo Ebola vaccine regimen.

Methods

In this sub-study of the EBOVAC-Salone Ebola vaccine trial in Sierra Leone, malaria microscopy was performed at the time of Ebola vaccination. Participants with symptomatic malaria were treated before vaccination. Ebola vaccine responses were assessed post-dose 1 (day 57) and post-dose 2 (day 78) by the EBOV glycoprotein FANG enzyme-linked immunosorbent assay (ELISA), and responses expressed as geometric mean concentrations (GMCs). Geometric mean ratios (GMRs) of the GMCs in malaria-positive versus malaria-negative participants were derived with 95% confidence intervals (CIs).

Results

A total of 587 participants were studied, comprising 188 adults (≥18 years) and 399 children (in age groups of 12–17, 4–11, and 1–3 years). Asymptomatic malaria was observed in 47.5% of adults and 51.5% of children on day 1. Post-dose 1, GMCs were lower in 1–3-year-old malaria-positive compared with malaria-negative children (age group–specific GMR, .56; 95% CI, .39–.81) but not in older age groups. Post-dose 2, there was no consistent effect of malaria infection across the different age groups but there was a trend toward a lower response (GMR, .82; 95% CI, .67–1.02).

Conclusions

The Ad26.ZEBOV, MVA-BN-Filo Ebola vaccine regimen is immunogenic in participants with asymptomatic malaria. Therefore, it is not necessary to screen for asymptomatic malaria infection prior to vaccination with this regimen.

Effect of intermittent preventive treatment for malaria with dihydroartemisinin-piperaquine on immune responses to vaccines among rural Ugandan adolescents: randomised controlled trial protocol B for the 'POPulation differences in VACcine responses' (POPVAC) programme

INTRODUCTION

Drivers of lower vaccine efficacy and impaired vaccine-specific immune responses in low-income versus high-income countries, and in rural compared with urban settings, are not fully elucidated. Repeated exposure to and immunomodulation by parasite infections may be important. We focus on Plasmodium falciparum malaria, aiming to determine whether there are reversible effects of malaria infection on vaccine responses.

METHODS AND ANALYSIS

We have designed a randomised, double-blind, placebo-controlled, parallel group trial of intermittent preventive malaria treatment versus placebo, to determine effects on vaccine response outcomes among school-going adolescents (9 to 17 years) from malaria-endemic rural areas of Jinja district (Uganda). Vaccines to be studied comprise BCG vaccine on day 'zero'; yellow fever, oral typhoid and human papilloma virus vaccines at week 4; and tetanus/diphtheria booster vaccine at week 28. Participants in the intermittent preventive malaria treatment arm will receive dihydroartemisinin/piperaquine (DP) dosed by weight, 1 month apart, prior to the first immunisation, followed by monthly treatment thereafter. We expect to enrol 640 adolescents. Primary outcomes are BCG-specific interferon-γ ELISpot responses 8 weeks after BCG immunisation and for other vaccines, antibody responses to key vaccine antigens at 4 weeks after immunisation. In secondary analyses, we will determine effects of monthly DP treatment (versus placebo) on correlates of protective immunity, on vaccine response waning, on whether there are differential effects on priming versus boosting immunisations, and on malaria infection prevalence. We will also conduct exploratory immunology assays among subsets of participants to further characterise effects of the intervention on vaccine responses.

ETHICS AND DISSEMINATION

Ethics approval has been obtained from relevant Ugandan and UK ethics committees. Results will be shared with Uganda Ministry of Health, relevant district councils, community leaders and study participants. Further dissemination will be done through conference proceedings and publications.

TRIAL REGISTRATION NUMBER

Current Controlled Trials identifier: ISRCTN62041885.

Meningococcal vaccines and protein-energy undernutrition in children in the African meningitis belt

BACKGROUND

Vaccines to prevent meningococcal meningitis in the African meningitis belt include PsACWY, a polysaccharide-only vaccine; and PsA-TT, a polysaccharide-protein conjugate vaccine. Protein-energy undernutrition, a condition where children do not receive enough macro- or micronutrients, is related to increased risk of infectious diseases and poor immune function. Reduced immune function could affect vaccine immunogenicity. We investigated connections between protein-energy undernutrition and vaccine immunogenicity and antibody waning to PsACWY and PsA-TT in children in the African meningitis belt.

METHODS

This is a secondary analysis of data collected as part of four clinical trials testing the safety and efficacy of PsA-TT in children in Mali, Ghana, and Senegal. We identified whether anthropometric growth indices (low height-for-age, weight-for-height, or weight-for-age Z-score categories) were related to reduced vaccine-elicited antibody (measured with rabbit complement) from pre- to 1 month post-vaccination, in linear regression models. We also identified whether these growth indices were related to increased waning for vaccine-elicited antibody over time, in linear regression models.

RESULTS

A total of 697 children were included in our analysis, of which 350 (50.2%) were female; the mean (SD) age was 1.0 (1.1) years, and 578 (83.0%) received PsA-TT. In linear regression models, no consistent statistical relationship was seen between pre-vaccination anthropometric Z-score categories and vaccine immunogenicity, or decline in antibody over time, for either vaccine, although children with low weight-for-height had a greater decline in antibody from 1 to 6 months post-vaccination.

CONCLUSIONS

Our analysis did not find protein-energy undernutrition to be associated with immunogenicity or waning of PsACWY- or PsA-TT-elicited antibody in children living in the African meningitis belt. Future studies should consider measuring antibody titers at additional time points post-vaccination, and for longer periods of time, to determine if the rate of antibody waning over a period of several years is associated with protein-energy undernutrition.

A Phase II, Randomized, Double-blind, Controlled Safety and Immunogenicity Trial of Typhoid Conjugate Vaccine in Children Under 2 Years of Age in Ouagadougou, Burkina Faso: A Methods Paper

The recent Typhoid Fever Surveillance in Africa Program demonstrated an overall adjusted incidence of typhoid fever 2–3 times higher than previous estimates in Africa. Recently, a single-dose typhoid conjugate vaccine that allows infants as young as 6 months old to be vaccinated was prequalified by the World Health Organization (WHO). This Vi-based conjugate vaccine demonstrated robust immunogenicity after 1 dose in infants and children 6 through 23 months of age in India with no safety signal, and is currently being tested for the first time on the African continent in Malawi. The WHO Strategic Advisory Group of Experts recommends studies to evaluate co-administering Vi-typhoid conjugate vaccine (Vi-TCV) with routine childhood vaccines in typhoid-endemic countries. The Burkina Faso immunization schedule includes yellow fever vaccine (YFV) at 9 months and meningococcal A conjugate vaccine (MCV-A) at 15 months, in addition to measles-rubella vaccine at both 9 and 15 months. Co-administration testing of Vi-TCV with these routine vaccinations will provide the data needed to support large-scale uptake of Vi-TCV in sub-Saharan Africa. A randomized, controlled, Phase II trial of Vi-TCV co-administration with the vaccinations routinely given at 9 and 15 months of age is planned in Burkina Faso. The overall aim is to assess the safety and immunogenicity of Vi-TCV when co-administered with YFV at 9 months of age and with MCV-A at 15 months of age. A total of 250 participants (100 infants aged 9–11 months and 150 children aged 15–23 months) will be enrolled.

Clinical Trials Registration. NCT03614533.

Factors That Influence the Immune Response to Vaccination

There is substantial variation between individuals in the immune response to vaccination. In this review, we provide an overview of the plethora of studies that have investigated factors that influence humoral and cellular vaccine responses in humans. These include intrinsic host factors (such as age, sex, genetics, and comorbidities), perinatal factors (such as gestational age, birth weight, feeding method, and maternal factors), and extrinsic factors (such as preexisting immunity, microbiota, infections, and antibiotics). Further, environmental factors (such as geographic location, season, family size, and toxins), behavioral factors (such as smoking, alcohol consumption, exercise, and sleep), and nutritional factors (such as body mass index, micronutrients, and enteropathy) also influence how individuals respond to vaccines. Moreover, vaccine factors (such as vaccine type, product, adjuvant, and dose) and administration factors (schedule, site, route, time of vaccination, and coadministered vaccines and other drugs) are also important. An understanding of all these factors and their impacts in the design of vaccine studies and decisions on vaccination schedules offers ways to improve vaccine immunogenicity and efficacy.

A Seroepidemiological Study of Serogroup A Meningococcal Infection in the African Meningitis Belt

The pattern of epidemic meningococcal disease in the African meningitis belt may be influenced by the background level of population immunity but this has been measured infrequently. A standardised enzyme-linked immunosorbent assay (ELISA) for measuring meningococcal serogroup A IgG antibodies was established at five centres within the meningitis belt. Antibody concentrations were then measured in 3930 individuals stratified by age and residence from six countries. Seroprevalence by age was used in a catalytic model to determine the force of infection. Meningococcal serogroup A IgG antibody concentrations were high in each country but showed heterogeneity across the meningitis belt. The geometric mean concentration (GMC) was highest in Ghana (9.09 μg/mL [95% CI 8.29, 9.97]) and lowest in Ethiopia (1.43 μg/mL [95% CI 1.31, 1.57]) on the margins of the belt. The force of infection was lowest in Ethiopia (λ = 0.028). Variables associated with a concentration above the putative protective level of 2 μg/mL were age, urban residence and a history of recent vaccination with a meningococcal vaccine. Prior to vaccination with the serogroup A meningococcal conjugate vaccine, meningococcal serogroup A IgG antibody concentrations were high across the African meningitis belt and yet the region remained susceptible to epidemics.

Malnutrition and vaccination in developing countries

Malnutrition contributes to an estimated 45% of deaths among children under 5 years of age in developing countries, predominantly due to infections. Malnourished children therefore stand to benefit hugely from vaccination, but malnutrition has been described as the most common immunodeficiency globally, suggesting that they may not be able to respond effectively to vaccines. The immunology of malnutrition remains poorly characterized, but is associated with impairments in mucosal barrier integrity, and innate and adaptive immune dysfunction. Despite this, the majority of malnourished children can mount a protective immune response following vaccination, although the timing, quality and duration of responses may be impaired. This paper reviews the evidence for vaccine immunogenicity in malnourished children, discusses the importance of vaccination in prevention of malnutrition and highlights evidence gaps in our current knowledge.

Plasmodium suppresses expansion of T cell responses to heterologous infections

Plasmodium remains a major pathogen causing malaria and impairing defense against other infections. Defining how Plasmodium increases susceptibility to heterologous pathogens may lead to interventions that mitigate the severity of coinfections. Previous studies proposed that reduced T cell responses during coinfections are due to diminished recruitment of naive T cells through infection-induced decreases in chemokine CCL21. We found that, although Listeria infections reduced expression of CCL21 in murine spleens, lymphocytic choriomeningitis virus (LCMV)-specific T cell responses were not impaired during Listeria + LCMV coinfection, arguing against a major role for this chemokine in coinfection-induced T cell suppression. In our experiments, Plasmodium yoelii infection led to a reduced CD8(+) T cell response to a subsequent Listeria infection. We propose an alternative mechanism whereby P. yoelii suppresses Listeria-specific T cell responses. We found that Listeria-specific T cells expanded more slowly and resulted in lower numbers in response to coinfection with P. yoelii. Mathematical modeling and experimentation revealed greater apoptosis of Listeria-specific effector T cells as the main mechanism, because P. yoelii infections did not suppress the recruitment or proliferation rates of Listeria-specific T cells. Our results suggest that P. yoelii infections suppress immunity to Listeria by causing increased apoptosis in Listeria-specific T cells, resulting in a slower expansion rate of T cell responses.

Plasmodium falciparum malaria and invasive bacterial co-infection in young African children: the dysfunctional spleen hypothesis

Children with recent or acute malaria episodes are at increased risk of invasive bacterial infections (IBI). However, the exact nature of the malaria-IBI association is still unclear. Young children have an age-related spleen immunologic immaturity, mainly due to the still ongoing development of the marginal zone (MZ) B cell subset. By mounting a rapid antibody response against encapsulated bacteria, these cells are critical for the defence against highly pathogenic microorganisms that do not elicit classical T cell-dependent responses. There is increasing evidence that the anatomy of the spleen becomes disorganized during malaria infection, with complete dissolution of the MZ and apoptosis of MZ B cells. Correspondingly, a reduction in the frequency of the peripheral equivalent of the MZ B cells has been found in malaria endemic areas. A remarkable similarity exists in IBI susceptibility between African children with malaria and hyposplenic or splenectomized patients. However, studies specifically assessing the immune function of the spleen in controlling bacterial infections in young children with malaria are scarce.

Here, it is hypothesized that Plasmodium falciparum malaria infection constitutes a detrimental factor in the still immature spleen function of young children, resulting in a factually hyposplenic state during malaria episodes, putting children with malaria at a high risk to develop life-threatening bacterial infections. Studies to confirm or reject this hypothesis are greatly needed, as well as the development of affordable and feasible tools to assess the immune spleen function against encapsulated bacteria in children with malaria.

The immune system in children with malnutrition--a systematic review

Background

Malnourished children have increased risk of dying, with most deaths caused by infectious diseases. One mechanism behind this may be impaired immune function. However, this immune deficiency of malnutrition has not previously been systematically reviewed.

Objectives

To review the scientific literature about immune function in children with malnutrition.

Methods

A systematic literature search was done in PubMed, and additional articles identified in reference lists and by correspondence with experts in the field. The inclusion criteria were studies investigating immune parameters in children aged 1–60 months, in relation to malnutrition, defined as wasting, underweight, stunting, or oedematous malnutrition.

Results

The literature search yielded 3402 articles, of which 245 met the inclusion criteria. Most were published between 1970 and 1990, and only 33 after 2003. Malnutrition is associated with impaired gut-barrier function, reduced exocrine secretion of protective substances, and low levels of plasma complement. Lymphatic tissue, particularly the thymus, undergoes atrophy, and delayed-type hypersensitivity responses are reduced. Levels of antibodies produced after vaccination are reduced in severely malnourished children, but intact in moderate malnutrition. Cytokine patterns are skewed towards a Th2-response. Other immune parameters seem intact or elevated: leukocyte and lymphocyte counts are unaffected, and levels of immunoglobulins, particularly immunoglobulin A, are high. The acute phase response appears intact, and sometimes present in the absence of clinical infection. Limitations to the studies include their observational and often cross-sectional design and frequent confounding by infections in the children studied.

Conclusion

The immunological alterations associated with malnutrition in children may contribute to increased mortality. However, the underlying mechanisms are still inadequately understood, as well as why different types of malnutrition are associated with different immunological alterations. Better designed prospective studies are needed, based on current understanding of immunology and with state-of-the-art methods.

Mycobacterium tuberculosis infection interferes with HIV vaccination in mice

Tuberculosis (TB) has emerged as the most prominent bacterial disease found in human immunodeficiency virus (HIV)-positive individuals worldwide. Due to high prevalence of asymptomatic Mycobacterium tuberculosis (Mtb) infections, the future HIV vaccine in areas highly endemic for TB will often be administrated to individuals with an ongoing Mtb infection. The impact of concurrent Mtb infection on the immunogenicity of a HIV vaccine candidate, MultiHIV DNA/protein, was investigated in mice. We found that, depending on the vaccination route, mice infected with Mtb before the administration of the HIV vaccine showed impairment in both the magnitude and the quality of antibody and T cell responses to the vaccine components p24Gag and gp160Env. Mice infected with Mtb prior to intranasal HIV vaccination exhibited reduced p24Gag-specific serum IgG and IgA, and suppressed gp160Env-specific serum IgG as compared to respective titers in uninfected HIV-vaccinated controls. Importantly, in Mtb-infected mice that were HIV-vaccinated by the intramuscular route the virus neutralizing activity in serum was significantly decreased, relative to uninfected counterparts. In addition mice concurrently infected with Mtb had fewer p24Gag-specific IFN-γ-expressing T cells and multifunctional T cells in their spleens. These results suggest that Mtb infection might interfere with the outcome of prospective HIV vaccination in humans.

Virus-induced transient immune suppression and the inhibition of T cell proliferation by type I interferon

Vaccine-induced memory is necessary for protective immunity to pathogens, but many viruses induce a state of transient immune suppression that might contribute to the inability of a vaccine to elicit immunity. We evaluated here the fate of bystander T cells activated by third party cognate antigens during acute viral infections in vivo, using distinct models to track and specifically activate HY and P14 transgenic bystander CD8 T cells in vivo during acute arenavirus infections of mice. Viral infections acted as stimulatory adjuvants when bystander T cells were exposed to an inflammatory milieu and cognate antigens at the beginning of infections, but bystander CD8 T cell proliferation in response to cognate antigen was inhibited 3 to 9 days after virus infection. Reduced proliferation was not dependent on Fas-FasL- or tumor necrosis factor (TNF)-induced activation-induced cell death or on deficiencies of antigen presentation. Instead, reduced proliferation was associated with a delayed onset of division that was an intrinsic defect of T cells. Inhibition of proliferation could be simulated by exposure of T cells to the Toll-like receptor agonist and type I interferon (IFN) inducer poly(I · C). T cells lacking IFN-α/β receptors resisted both the suppressive effects of preexposure to poly(I · C) and the stimulatory effects of type I IFN, indicating that the timing of exposure to IFN can have negative or positive effects on T cell proliferation. Inhibition of T cell receptor-stimulated bystander CD8 T cell proliferation during acute viral infections may reflect the reduced ability of vaccines to elicit protective immunity when administered during an acute illness.

Malaria exacerbates experimental mycobacterial infection in vitro and in vivo

Tuberculosis (Mtb) and malaria are among the most important infectious causes of morbidity and mortality worldwide, causing an estimated 1.5 million and 1 million deaths every year, respectively. Here we demonstrate a biological interaction between malaria and mycobacteria in vitro and in vivo. Murine macrophages co-incubated with Plasmodium falciparum parasitized erythrocytes demonstrated impaired control of intracellular Mtb replication, and reduced production of reactive nitrogen species in response to mycobacteria. Infection of C57BL/6 mice with Plasmodium species exacerbated the course of acute mycobacterial infection (57% increase in peak splenic CFU, p = 0.043 for difference over time course of infection), induced disruption of the structural integrity of established granulomas, and caused reactivation of latent mycobacterial infection (2.6-fold increase in peak splenic CFU, p = 0.016 for difference over time course of reactivation). Malaria pigment deposition within the granulomas of co-infected mice suggested that the influx of dysfunctional hemozoin-laden monocytes into the locus of mycobacterial control may contribute to impaired containment of mycobacteria. Collectively, these results point to malaria-induced dysregulation of innate and adaptive anti-mycobacterial defences, and suggest that the interaction of these globally important pathogens may potentiate Mtb infection and transmission.

Landscape analysis of interactions between nutrition and vaccine responses in children

The world's poorest children are likely to be malnourished when receiving their childhood vaccines. It is uncertain whether this affects vaccine efficacy and whether the coadministration of nutrient supplements with vaccines has beneficial or detrimental effects. More recently, a detrimental interaction between vitamin A (VA) supplementation (VAS) and the killed diphtheria-tetanus-pertussis vaccine given in early childhood has been suggested. This report provides a critical review of the published interactions between nutritional status and/or supplementation and vaccine responses in children. Due to an absence of evidence for most nutrients, this analysis focused on protein-energy, vitamins A and D, and iron and zinc. All vaccines were considered. Both observational studies and clinical trials that led to peer-reviewed publications in English or French were included. These criteria led to a pool of 58 studies for protein-energy malnutrition, 43 for VA, 4 for vitamin D, 10 for iron, and 22 for zinc. Our analysis indicates that malnutrition has surprisingly little or no effect on vaccine responses. Evidence for definitive adjunctive effects of micronutrient supplementation at the time of vaccination is also weak. Overall, the paucity, poor quality, and heterogeneity of data make it difficult to draw firm conclusions. The use of simple endpoints that may not correlate strongly with disease protection adds uncertainty. A detailed examination of the immunological mechanisms involved in potential interactions, employing modern methodologies, is therefore required. This would also help us understand the proposed, but still unproven, negative interactions between VAS and vaccine safety, a resolution of which is urgently required.

Enhanced Toll-like receptor responsiveness associated with mitogen-activated protein kinase activation in Plasmodium falciparum-infected children

Acute Plasmodium falciparum infection is associated with strongly upregulated cytokine responses that are at least partly the result of activation of Toll-like receptors (TLRs). Whether and how TLR expression/responsiveness changes upon malarial infection is, however, currently not well understood. To assess this, we examined expression of TLRs and used the TLR ligand lipopolysaccharide (LPS) and Pam(3)Cys to stimulate peripheral blood mononuclear cells (PBMCs) from Ghanaian schoolchildren who live in a rural area where P. falciparum is endemic. Expression of TLR2 was higher, and responses to its ligand, Pam(3)Cys, were enhanced in P. falciparum-infected children compared to their uninfected counterparts. In cells from the same children, stimulation by Pam(3)Cys resulted in higher p38 mitogen-activated protein kinase activation and higher cytokine production. In vitro experiments confirmed that preincubation of PBMCs with P. falciparum-infected red blood cells enhanced responsiveness to TLR ligands. Taken together, the data indicate that P. falciparum-infected children in areas where malaria is endemic have an altered innate immune system, which might be important for the balance between immunity and pathology when new infections are encountered or when novel vaccines are introduced.

Suppression of adaptive immunity to heterologous antigens during Plasmodium infection through hemozoin-induced failure of dendritic cell function

BACKGROUND

Dendritic cells (DCs) are central to the initiation and regulation of the adaptive immune response during infection. Modulation of DC function may therefore allow evasion of the immune system by pathogens. Significant depression of the host's systemic immune response to both concurrent infections and heterologous vaccines has been observed during malaria infection, but the mechanisms underlying this immune hyporesponsiveness are controversial.

RESULTS

Here, we demonstrate that the blood stages of malaria infection induce a failure of DC function in vitro and in vivo, causing suboptimal activation of T cells involved in heterologous immune responses. This effect on T-cell activation can be transferred to uninfected recipients by DCs isolated from infected mice. Significantly, T cells activated by these DCs subsequently lack effector function, as demonstrated by a failure to migrate to lymphoid-organ follicles, resulting in an absence of B-cell responses to heterologous antigens. Fractionation studies show that hemozoin, rather than infected erythrocyte (red blood cell) membranes, reproduces the effect of intact infected red blood cells on DCs. Furthermore, hemozoin-containing DCs could be identified in T-cell areas of the spleen in vivo.

CONCLUSION

Plasmodium infection inhibits the induction of adaptive immunity to heterologous antigens by modulating DC function, providing a potential explanation for epidemiological studies linking endemic malaria with secondary infections and reduced vaccine efficacy.

Malaria chemoprophylaxis and the serologic response to measles and diphtheria-tetanus-whole-cell pertussis vaccines

Background

Acute malaria has been associated with a decreased antibody response to tetanus and diphtheria toxoids, meningococcal, salmonella, and Hib vaccines. Interest in giving malaria drug therapy and prevention at the time of childhood immunizations has increased greatly following recent trials of intermittent preventive therapy during infancy (IPTi), stimulating this re-analysis of unpublished data. The effect of malaria chemoprophylaxis on vaccine response was studied following administration of measles vaccines and diphtheria-tetanus-whole cell pertussis (DTP) vaccines.

Methods

In 1975, six villages divided into two groups of children ≤74 months of age from Burkina Faso, were assigned to receive amodiaquine hydrochloride chemoprophylaxis (CH+) every two weeks for seven months or no chemoprophylaxis (CH-). After five months, children in each group received either one dose of measles or two doses of DTP vaccines.

Results

For recipients of the measles vaccine, the seroconversion rates in CH+ and CH- children, respectively, were 93% and 96% (P > 0.05). The seroresponse rates in CH+ and CH- children respectively, were 73% and 86% for diphtheria (P > 0.05) and 77% and 91% for tetanus toxoid (P > 0.05). In a subset analysis, in which only children who strictly adhered to chemoprophylaxis criteria were included, there were, likewise, no significant differences in seroconversion or seroresponse for measles, diphtheria, or tetanus vaccines (P > 0.05). While analysis for pertussis showed a 43% (CH+) and 67% (CH-) response (P < 0.05), analyses using logistic regression to control for sex, age, chemoprophylaxis, weight-for-height Z-score, and pre-vaccination geometric mean titer (GMT), demonstrated that chemoprophylaxis was not associated with a significantly different conversion rate following DTP and measles vaccines. Seven months of chemoprophylaxis decreased significantly the malaria IFA and ELISA GMTs in the CH+ group.

Conclusion

Malaria chemoprophylaxis prior to vaccination in malaria endemic settings did not improve or impair immunogenicity of DTP and measles vaccines. This is the first human study to look at the association between malaria chemoprophylaxis and the serologic response to whole-cell pertussis vaccine.

Peripheral blood dendritic cells in children with acute Plasmodium falciparum malaria

The importance of dendritic cells (DCs) for the initiation and regulation of immune responses not only to foreign organisms but also to the self has raised considerable interest in the qualitative and quantitative analysis of these cells in various human diseases. Plasmodium falciparum malaria is characterized by the poor induction of long-lasting protective immune responses. This study, therefore, investigated the percentage of peripheral blood DCs as lineage marker-negative and HLA-DR(+) or CD83(+) cells in healthy children and in children suffering from acute malaria in Kilifi, Kenya. Comparable percentages of CD83(+) DCs were found in peripheral blood of healthy children and children with malaria. However, the percentage of HLA-DR(+) peripheral blood DCs was significantly reduced in children with malaria. The results suggest that a proportion of peripheral blood DCs may be functionally impaired due to the low expression of HLA-DR on their surface.

Timely detection of meningococcal meningitis epidemics in Africa

BACKGROUND

Epidemics of meningococcal disease in Africa are commonly detected too late to prevent many cases. We assessed weekly meningitis incidence as a tool to detect epidemics in time to implement mass vaccination.

METHODS

Meningitis incidence for 41 subdistricts in Mali was determined from cases recorded in health centres (1989-98) and from surveillance data (1996-98). For incidence thresholds of 5 to 20 cases per 100000 inhabitants per week, we calculated sensitivity and specificity for detecting epidemics, and determined the time lapse between threshold and epidemic peak.

FINDINGS

We recorded 9084 meningitis cases. Clinic-based weekly incidence of 5 and 10 cases per 100000 inhabitants detected all meningitis epidemics (sensitivity 100%, 95% CI 93-100), with median threshold-to-peak time of 5 and 3 weeks. Under-reporting reduced sensitivity: only surveillance thresholds of 5 or 7 cases per 100000 inhabitants per week detected all epidemics. Crossing the lower threshold before the 10th calendar week doubled epidemic risk relative to crossing it later (relative risk 2.1, 95% CI 1.4-3.2). At 10 cases per 100000 inhabitants per week, specificity for outbreak prediction was 88%, 95% CI 83-91). For populations under 30000, 3 to 5 cases in one or two weeks predicted epidemics with 85% to 97% specificity.

INTERPRETATION

Low meningitis thresholds improve timely detection of epidemics. Ten cases per 100000 inhabitants per week in one area confirm epidemic activity in a region, with few false alarms. An alert threshold of 5 cases per 100000 inhabitants per week allows time to investigate, prepare for an epidemic, and initiate mass vaccination where appropriate. For populations under 30000, the alert threshold is two cases in a week. High quality surveillance is essential.

A role for CD36 in the regulation of dendritic cell function

Dendritic cells (DC) are crucial for the induction of immune responses and thus an inviting target for modulation by pathogens. We have previously shown that Plasmodium falciparum-infected erythrocytes inhibit the maturation of DCs. Intact P. falciparum-infected erythrocytes can bind directly to CD36 and indirectly to CD51. It is striking that these receptors, at least in part, also mediate the phagocytosis of apoptotic cells. Here we show that antibodies against CD36 or CD51, as well as exposure to early apoptotic cells, profoundly modulate DC maturation and function in response to inflammatory signals. Although modulated DCs still secrete tumor necrosis factor-alpha, they fail to activate T cells and now secrete IL-10. We therefore propose that intact P. falciparum-infected erythrocytes and apoptotic cells engage similar pathways regulating DC function. These findings may have important consequences for the treatment of malaria and may suggest strategies for modulating pathological immune responses in autoimmune diseases.

Plasmodium falciparum-infected erythrocytes modulate the maturation of dendritic cells

The malaria parasite Plasmodium falciparum is one of the most successful human pathogens. Specific virulence factors remain poorly defined, although the adhesion of infected erythrocytes to the venular endothelium has been associated with some of the syndromes of severe disease. Immune responses cannot prevent the development of symptomatic infections throughout life, and clinical immunity to the disease develops only slowly during childhood. An understanding of the obstacles to the development of protective immunity is crucial for developing rational approaches to prevent the disease. Here we show that intact malaria-infected erythrocytes adhere to dendritic cells, inhibit the maturation of dendritic cells and subsequently reduce their capacity to stimulate T cells. These data demonstrate both a novel mechanism by which malaria parasites induce immune dysregulation and a functional role beyond endothelial adhesion for the adhesive phenotypes expressed at the surface of infected erythrocytes.

Control of group C meningococcal disease in Australian aboriginal children by mass rifampicin chemoprophylaxis and vaccination

An outbreak of 12 cases of meningitis, 11 caused by Neisseria meningitidis serogroup C, occurred at Doomadgee from September, 1990, to April, 1991. The incidence of meningitis was 17.55/10(3) person-years. Only children aged 1-10 years were affected. In October, 1990, or shortly thereafter, 473/509 children aged between 1 and 15 years inclusive had one dose of Mencevax AC. From the time of vaccination until April, 1991, a further eight cases occurred, six in vaccinated children. Vaccine efficacy in 1-15 year olds was calculated as 77%. Despite this, in April, 1991, the prevalence of antibody to group C polysaccharide in vaccinated children (78%) was not significantly different from that in unvaccinated children and adults. 46 nonresponders were revaccinated, and, in February, 1992, 78% had antibodies to group C polysaccharide. In April, 1991, an estimated 3.0% of the population had group C organisms, carriage being directly related to household crowding. In June, 1991, 2 months after mass prophylaxis with rifampicin, none of these individuals were carriers. In October, 1991, the carriage rate of group C organisms was 0.64%. There have been no further cases caused by the epidemic strain. Although uncrowded housing is a basic need, mass chemoprophylaxis and two doses of vaccine for children should be used in similar outbreaks.

Genetic epidemiology of the beta s gene

The beta s gene arose at least four times in Africa, with three of these mutations expanding through diverse ethnic groups, but limited to definite geographical areas: Atlantic west Africa for the Senegal haplotype linked beta s; central west Africa for the Benin haplotype; and equatorial, eastern and southern Africa for the Bantu haplotype. The fourth mutation (linked to the Cameroon haplotype) is restricted to a single ethnic group, the Eton of central Cameroon. The Benin haplotype linked beta s gene was spread by gene flow to the Mediterranean (north, south and east) and to the western portions of Saudi Arabia. An independent mutation linked to a fifth haplotype, Arab-India, is found among the tribals of India (independent from their geographical origin) and in the eastern oases of Saudi Arabia. It is also suspected of being associated with the beta s gene found in Afghanistan, Iran, Transcaucasia and central Asia. The selective force involved in the expansion of the gene was most likely P. falciparum malaria, and the time of the gene frequency increase was likely to have been during the expansion of agriculture about 4000 or more years ago in India and about 3000 years ago in Africa. The partial protection against severe and life-threatening malaria is through the limitation of P. falciparum parasitaemia. This is a complex process which involves at least two mechanisms: early intraerythrocyte parasite forms are in a suicidal position through increasing the tendency of HbAS cell to sickle and then be destroyed by the spleen; intraerythrocyte growth is inhibited during deep vascular schizogony. Although there is evidence that P. falciparum (and P. malariae) parasitaemias are limited in HbSS red cells, malaria is a major trigger to haemolytic and infarctive crises in sickle-cell disease, and a common cause of morbidity and mortality.

Malaria: drug use and the immune response

Malaria is a controllable disease, yet the resources required - human, technical and financial - are massive, and are currently beyond the vast majority of the 96 countries where the disease is endemic. The control measures most widely applied are vector control through spraying or use of insecticide-impregnated bednets, and chemotherapy. The biological problems to add to the resource issues are well known; increasing resistance of anopheline mosquitoes to the most widely used insecticides, and the progressive development of drug resistance in the parasite populations, especiallyPlasmodium falciparum.

Impaired antibody response to Haemophilus influenzae type b polysaccharide and low IgG2 and IgG4 concentrations in Apache children

BACKGROUND AND METHODS

Because Native American children are at much higher risk for invasive Haemophilus influenzae type b infection than white children, we compared the antibody responses to H. influenzae type b polysaccharide vaccine in healthy Apache and white children.

RESULTS

The concentrations of H. influenzae type b antibody after immunization with polysaccharide vaccine were approximately 10-fold lower in 24-month-old Apache children than in whites of a similar age (P less than 0.01). The decreased response involved H. influenzae type b antibodies of the IgG, IgM, and IgA classes. Concentrations of IgG antibody to tetanus toxoid did not differ significantly, and IgG antibodies to diphtheria toxoid were only twofold lower (P = 0.028). Although total IgG, IgM, and IgA levels were higher in two-year-old Apaches than in whites (all P less than 0.001), IgG2 and IgG4 subclasses were lower (both P less than 0.001). Among the Apaches, individual immunoglobulin levels and allotypes were not significantly correlated with their antibody responses to H. influenzae type b polysaccharide.

CONCLUSIONS

Apache children have significant impairment of their antibody response to H. influenzae type b polysaccharide and little or no impairment of their antibody responses to protein toxoids. This immunodeficiency may explain the high incidence of H. influenzae type b infection in this population.

Features of a large epidemic of group A meningococcal meningitis in Khartoum, Sudan in 1988

A large epidemic (February-August 1988) of group A sulphonamide resistant, clone III-1 meningococcal meningitis in Khartoum, Sudan is described. A total of 10,099 cases were admitted to treatment centers with 8,397 cases during March and April, corresponding to an annual incidence of 1,679/100,000 inhabitants during this period. The age profile showed a high morbidity in adults (31% of the cases greater than or equal to 20 years). The male dominance was marked especially in the adult cases with a proportion of 3.2:1. The epidemic started during the hot and dry season and declined when the clouds came, humidity rose, temperature fell and a mass vaccination campaign had been implemented together with other epidemic precautions. Vaccination with a combined group A/C polysaccharide vaccine had been given 4 weeks-1 year before hospitalization to 11% of the children, 80% of whom were greater than 18 months of age. The estimated case fatality rate was 6.3%. Since 47% of the cases came from periurban and rural areas, the actual mortality during the epidemic might have been higher when considering those who may have died before reaching any of the treatment centres. Fatal cases had a short history of acute illness and a septic condition. Septicaemia was rare and seen in only 3.7% of the cases, the rest had acute purulent meningitis. Hearing loss/impairment and hemiplegia was diagnosed in 2-3% of the cases. The epidemiology, based on detailed typing/subtyping and restriction enzyme patterns of meningococcal strains, was apparently associated with the Mecca outbreak in August 1987.

Class-specific antibodies to Bordetella pertussis, Haemophilus influenzae type b, Streptococcus pneumoniae and Neisseria meningitidis in human breast-milk and maternal-infant sera

Children under 2 years of age are most susceptible to acute respiratory infections caused by Bordetella pertussis, Haemophilus influenzae type b, Streptococcus pneumoniae and Neisseria meningitidis. We analysed milk samples and sera from mother-infant pairs for specific antibodies that may enhance protection against the bacterial pathogens. The results show that the breast-milk samples contained significant titres of specific IgG and IgA antibodies to the four organisms, although the mean IgG antibody levels were higher in maternal sera than in breast-milk. On the other hand, the mean IgA antibody levels to the four organisms were higher in breast-milk than in both maternal and infant sera. IgM antibodies to these organisms were relatively low or absent in many milk and serum samples. Nevertheless, the significant concentrations of specific IgG and IgA antibodies in milk samples may indicate a protective role for breast-milk against the four infections in early childhood.

The effect of pentostam and cimetidine on the development of leishmaniasis (Leishmania mexicana amazonensis) and concomitant malaria (Plasmodium yoelii)

BALB/c mice were infected with Leishmania mexicana amazonensis and/or Plasmodium yoelii in order to determine the impact of multiple parasitic infection on the efficacy of chemotherapeutic agents. Uninfected, P. yoelii-infected, L.m. amazonensis-infected, and L.m. amazonensis and P. yoelii-infected mice were inoculated with cimetidine (80 mg kg-1 day-1) or pentostam (200 mg kg-1 day-1) once a day for an initial 20-day period, and once a week thereafter. Leishmania mexicana amazonensis lesion development and P. yoelii parasitaemia were the criteria used to assay disease severity. Mice infected with both P. yoelii and L.m. amazonensis developed more severe disease than did animals infected with either parasite alone. Cimetidine and pentostam each slowed the development of L.m. amazonensis in animals infected with only that parasite and in animals infected with both P. yoelli and L.m. amazonensis. However, mice treated with pentostam developed more severe P. yoelii infections than did control animals, whereas cimetidine significantly reduced P. yoelii parasitaemia in all instances.

Malaria chemoprophylaxis with chloroquine in young Nigerian children. II. Effect on the immune response to vaccination

The immune response of 198 young Nigerian children protected against malaria by chemoprophylaxis with chloroquine to immunization with triple, poliomyelitis, measles, typhoid, meningococcal and BCG vaccines was compared with the immune response to vaccination of 185 control children. Good responses to triple, measles and BCG vaccines were shown by children in both groups; poorer responses were obtained to poliomyelitis, typhoid and meningococcal vaccines. The response to immunization of protected children was similar to that observed among control children for all the vaccines tested except for meningococcal polysaccharide vaccine. Protected children showed a significantly greater antibody response to both group A and group C meningococcal polysaccharides than control children. This finding supports the results of previous studies which have shown that the immune response to meningococcal polysaccharide vaccines is adversely affected both by acute malaria and by asymptomatic malaria parasitaemia.

Control of epidemic meningococcal meningitis by mass vaccination. II. Persistence of antibody four years after vaccination

Meningococcal antibody was measured in 928 persons vaccinated with combined groups A and C polysaccharide antigens in Bauchi State, Nigeria between 1979 and 1982. Protective amounts of antibody were detected by the indirect haemagglutination technique up to 4 years after vaccination. This persistence was observed mainly in adults, although a substantial proportion of older children also had persistent antibody. Titres in younger children fell progressively, and by the third year the mean log2 antibody titre was 1.4; this may not confer protection against disease. A rational policy for vaccination against meningococcal meningitis would be to revaccinate younger children after 2 years, older children after 4 years, and adults after 6-8 or more years.

Epidemic of meningococcal meningitis in Bamako, Mali: epidemiological features and analysis of vaccine efficacy

Many studies have demonstrated the efficacy of meningococcal vaccine in nonepidemic meningococcal meningitis, but few have examined its efficacy in epidemic conditions. The effects of the vaccine on the course of a meningococcal meningitis epidemic in Bamako, Mali, between January and April, 1981, were studied. The vaccine was effective in limiting further spread of the epidemic. The attack rate among those who received vaccine was lower than that in the unvaccinated (0.7/10 000 vs 4.7/10 000), and the case-fatality rate among vaccinees in whom meningitis developed was lower than that of the unvaccinated. Routine vaccination against meningococcal meningitis in Africa may be impracticable owing to the cost, the relatively short duration of effectiveness, and the irregular occurrence of epidemics. Vaccination early in the course of an epidemic, however, appears to be a useful and practicable method of limiting the spread of disease.

The immunological response to polyvalent meningococcal vaccine in Bauchi State, Nigeria

The post-vaccination antibody response to both Group A and Group C meningococcal polysaccharide antigen was studied in 397 male and 359 female vaccinated persons aged between 4 and 40 years from Bauchi Town and neighbouring villages in Nigeria. No difference in response was observed between the sexes. Highest antibody levels occurred in those aged between 13 and 28 years. Haemoglobin genotype did not affect response. Malnourished children had significantly lower mean IgG, IgA and IgM levels and the response to meningovaccine was also lower than in normal children.

The duration of the antibody response to meningococcal vaccination in an African village

Sera were obtained from 119 Nigerian villagers two years after immunization with group A and group C meningococcal polysaccharide vaccines. Measurement of meningococcal antibody levels in individual serum samples by the haemagglutination technique showed that two years after vaccination the mean group A meningococcal antibody level was no higher in immunized subjects than in 140 age-matched, non-immunized controls. Over-all the mean group C meningococcal haemagglutinating antibody level was significantly higher in immunized subjects than it was in controls but this difference was not found in those under the age of 15 years at the time of vaccination. However, when pooled serum samples from the same subjects were tested for meningococcal antibodies by radioimmunoassay, immunized subjects were found to have significantly higher mean levels of both group A and group C meningococcal antibodies than the controls. The possible reasons for this discrepancy are considered and the significance of these findings in relation to plans for mass immunization with meningococcal vaccines in tropical Africa are discussed.