Peter Mungai

In utero exposure to helminth and mycobacterial antigens generates cytokine responses similar to that observed in adults.

Neonates exposed to parasite antigens (Ags) in utero may develop altered fetal immunity that could affect subsequent responses to infection. We hypothesized that cord blood lymphocytes (CBL) from offspring of mothers residing in an area highly endemic for schistosomiasis, filariasis, and tuberculosis in Kenya would either fail to respond or generate a predominantly Th2-associated cytokine response to helminth and mycobacterial antigens (PPD) in vitro compared to maternal PBMC. Kenyan CBL generated helminth Ag-specific IL-5 (range 29-194 pg/ml), IL-10 (121-2,115 pg/ml), and/or IFN-gamma (78 pg/ml-10.6 ng/ml) in 26, 46, and 57% of neonates, respectively (n = 40). PPD induced IFN-gamma in 30% of Kenyan CBL (range 79-1,896 pg/ml), but little or no IL-4 or IL-5. No Ag-specific IL-4, IL-5, or IFN-gamma release was detected by CBL obtained in the United States (n = 11). Ag-driven cytokine production was primarily CD4-dependent. Cytokine responses to helminth and mycobacterial Ags by maternal PBMC mirrored that observed in neonates. CBL from helminth infected and/or PPD-sensitized mothers produced more Ag-specific cytokines compared to CBL from uninfected mothers (P < 0.05). These data demonstrate that the human fetus develops similar patterns of cytokine production observed in adults and indicates that prenatal exposure may not lead to tolerance or altered fetal immunity. .

Can Prenatal Malaria Exposure Produce an Immune Tolerant Phenotype?: A Prospective Birth Cohort Study in Kenya

In a prospective cohort study of newborns residing in a malaria holoendemic area of Kenya, Christopher King and colleagues find a subset of children born to malaria-infected women who acquire a tolerant phenotype, which persists into childhood and is associated with increased susceptibility to malarial infection and anemia.

Acquired Immune Responses to Plasmodium falciparum Merozoite Surface Protein-1 in the Human Fetus

Infants born in areas of stable malaria transmission are relatively protected against severe morbidity and high density Plasmodium falciparum blood-stage infection. This protection may involve prenatal sensitization and immunologic reactivity to malaria surface ligands that participate in invasion of red cells. We examined cord blood T and B cell immunity to P. falciparum merozoite surface protein-1 (MSP-1) in infants born in an area of stable malaria transmission in Kenya. T cell cytokine responses to the C-terminal 19-kDa fragment of MSP-1 (MSP-119) were detected in 24 of 92 (26%) newborns (4–192 IFN-γ and 3–88 IL-4-secreting cells per 106/cord blood lymphocytes). Peptide epitopes in the N-terminal block 3 region of MSP-1 also drove IFN-γ and/or IL-13 production. There was no evidence of prenatal T cell sensitization to liver-stage Ag-1. A total of 5 of 86 (6%) newborns had cord blood anti-MSP-119 IgM Abs, an Ig isotype that does not cross the placenta and is therefore of fetal origin. The frequency of neonatal B cell sensitization was higher than that indicated by serology alone, as 5 of 27 (18%) cord blood samples contained B cells that produced IgG when stimulated with MSP-119 in vitro. Neonatal B cell IgG responses were restricted to the Q-KNG allele of MSP-119, the major variant in this endemic area, whereas T cells responded to all four MSP-119 alleles evaluated. In utero sensitization to MSP-1 correlated with the presence of malaria parasites in cord blood (χ2 = 20, p < 0.0001). These data indicate that prenatal sensitization to blood-stage Ags occurs in infants born in malaria endemic areas.

The Effects of Maternal Helminth and Malaria Infections on Mother-to-Child HIV Transmission

Objective:To investigate the effect of helminth and/or malaria infection on the risk of HIV infection in pregnant women and its transmission to their offspring. Design:A retrospective cohort study of pregnant Kenyan women and their offspring from term, uncomplicated vaginal deliveries (n = 936) with a nested case–control study. Methods:We determined the presence of HIV, malaria, schistosomiasis, lymphatic filariasis, and intestinal helminthes in mothers and tested for HIV antibodies in 12-24 month-old offspring of HIV-positive women. We related these findings to the presence of cord blood lymphocyte activation and cytokine production in response to helminth antigens. Results:HIV-positive women (n = 83, 8.9% of all women tested) were 2-fold more likely to have peripheral blood and/or placental malaria (P < 0.025) and a 2.1-fold greater likelihood of lymphatic filariasis infection (P < 0.001) compared to location-and-parity matched HIV-negative women. Women with HIV and malaria tended to show an increased risk for mother-to-child-transmission (MTCT) of HIV, although this difference was not significant. MTCT of HIV, however, was significantly higher in women co-infected with one or more helminthes (48%) verses women without helminth infections (10%, P < 0.01; adjusted odds ratio, 7.3; 95% confidence interval, 2.4–33.7). This increased risk for MTCT of HIV correlated with cord blood lymphocytes production of interleukin-5/interleukin-13 in response to helminth antigens (P < 0.001). Conclusion:Helminth co-infection is associated with increased risk for MTCT of HIV, possibly by a mechanism in which parasite antigens activates lymphocytes in utero. Treatment of helminthic infections during pregnancy may reduce the risk of MTCT of HIV.

Distinct Th1- and Th2-Type Prenatal Cytokine Responses to Plasmodium falciparum Erythrocyte Invasion Ligands

ABSTRACT Prenatal immunity to Plasmodium falciparum merozoite proteins involved in erythrocyte invasion may contribute to the partial protection against malaria that is acquired during infancy in areas of stable malaria transmission. We examined newborn and maternal cytokine and antibody responses to merozoite surface protein-1 (MSP-1), ribosomal phosphoprotein P0 (PfP0), and region II of erythrocyte binding antigen-175 (EBA-175) in infant-mother pairs in Kenya. Overall, 82 of 167 (50%), 106 of 176 (60%), and 38 of 84 (45%) cord blood lymphocytes (CBL) from newborns produced one or more cytokines in response to MSP-1, PfP0, and EBA-175, respectively. Newborns of primigravid and/or malaria-infected women were more likely to have antigen-responsive CBL than were newborns of multigravid and/or uninfected women at delivery. Newborn cytokine responses did not match those of their mothers and fell into three distinct categories, Th1 (21 of 55 CBL donors produced only gamma interferon and/or interleukin 2 [IL-2]), Th2 (21 of 55 produced only IL-5 and/or IL-13), and mixed Th1/Th2 (13 of 55). Newborns produced more IL-10 than adults. High and low levels of cord blood IL-12 p70 production induced by anti-CD40 activation were associated with malaria-specific Th1 and Th2 responses, respectively. Antigen-responsive CBL in some newborns were detected only after depletion of IL-10-secreting CD8 cells with enrichment for CD4 cells. These data indicate that prenatal sensitization to blood-stage Plasmodium falciparum occurs frequently in areas where malaria is holoendemic. Modulation of this immunity, possibly by maternal parity and malaria, may affect the acquisition of protective immunity against malaria during infancy.

Impact of insecticide-treated bed nets on malaria transmission indices on the south coast of Kenya

BackgroundBesides significantly reducing malaria vector densities, prolonged usage of bed nets has been linked to decline of Anopheles gambiae s.s. relative to Anopheles arabiensis, changes in host feeding preference of malaria vectors, and behavioural shifts to exophagy (outdoor biting) for the two important malaria vectors in Africa, An. gambiae s.l. and Anopheles funestus. In southern coastal Kenya, bed net use was negligible in 1997-1998 when Anopheles funestus and An. gambiae s.s. were the primary malaria vectors, with An. arabiensis and Anopheles merus playing a secondary role. Since 2001, bed net use has increased progressively and reached high levels by 2009-2010 with corresponding decline in malaria transmission.MethodsTo evaluate the impact of the substantial increase in household bed net use within this area on vector density, vector composition, and human-vector contact, indoor and outdoor resting mosquitoes were collected in the same region during 2009-2010 using pyrethrum spray catches and clay pots for indoor and outdoor collections respectively. Information on bed net use per sleeping spaces and factors influencing mosquito density were determined in the same houses using Poisson regression analysis. Species distribution was determined, and number of mosquitoes per house, human-biting rates (HBR), and entomological inoculation rate (EIR) were compared to those reported for the same area during 1997-1998, when bed net coverage had been minimal.ResultsCompared to 1997-1998, a significant decline in the relative proportion of An. gambiae s.s. among collected mosquitoes was noted, coupled with a proportionate increase of An. arabiensis. Following > 5 years of 60-86% coverage with bed nets, the density, human biting rate and EIR of indoor resting mosquitoes were reduced by more than 92% for An. funestus and by 75% for An. gambiae s.l. In addition, the host feeding choice of both vectors shifted more toward non-human vertebrates. Besides bed net use, malaria vector abundance was also influenced by type of house construction and according to whether one sleeps on a bed or a mat (both of these are associated with household wealth). Mosquito density was positively associated with presence of domestic animals.ConclusionsThese entomological indices indicate a much reduced human biting rate and a diminishing role of An. gambiae s.s. in malaria transmission following high bed net coverage. While increasing bed net coverage beyond the current levels may not significantly reduce the transmission potential of An. arabiensis, it is anticipated that increasing or at least sustaining high bed net coverage will result in a diminished role for An. funestus in malaria transmission.

Prenatal T Cell Immunity to Wuchereria bancrofti and Its Effect on Filarial Immunity and Infection Susceptibility during Childhood

BACKGROUND Antenatal immune experience with Wuchereria bancrofti due to maternal filariasis may influence susceptibility to infection. We tested the hypothesis that filarial-specific T cell responses at birth that are indicative of in utero tolerance or sensitization affect the evolution of filarial-specific immunity and susceptibility to W. bancrofti infection during childhood. METHODS A birth-cohort study of 159 Kenyan newborns was performed. Cord blood and peripheral blood were obtained annually to age 7 years and were assayed for filarial infection and filarial antigen-driven interferon (IFN)- gamma , interleukin (IL)-2, IL-5, and IL-13 production by lymphocytes. RESULTS There was a 12.9-fold (95% confidence interval [CI], 2.5-107.2-fold) and a 4.8-fold (95% CI, 1.7-12.9-fold) increased risk of infection for immune-tolerant newborns (maternal infection present during gestation, with no filarial antigen-driven cord blood T cell response [n = 25]), compared with immune-sensitized (maternal infection present with cord blood T cell response [n = 24]) and unexposed (maternal infection absent [n = 110]) newborns. Cytokine responses developed at a later age in tolerant newborns, were characterized by impaired IFN-gamma responses, and contrasted with those of filarial-sensitized newborns, who had sustained and elevated IL-5 and IL-13 responses to age 7 years. CONCLUSION Prenatal immune experience, as determined by whether in utero priming to filarial antigen occurs, is a major determinant of childhood susceptibility to W. bancrofti infection.

Real-Time Quantitative PCR for Determining the Burden of Plasmodium falciparum Parasites during Pregnancy and Infancy

ABSTRACT Real-time quantitative PCR (RTQ-PCR) provides a quick, accurate, and reproducible quantification of parasites. However, the value of RTQ-PCR for predicting clinical outcomes of malaria is unknown. Here, we compared RTQ-PCR to microscopy of blood smears, nested PCR (nPCR), and parasite circulating-antigen (CAg) assays for detection of Plasmodium falciparum in pregnant Kenyan women and their infants and related these findings to parity and birth weights in their newborns (n = 554). nPCR was the most sensitive assay for detection of malaria in pregnancy, followed in decreasing order of sensitivity by RTQ-PCR, CAg assays, and blood smears. RTQ-PCR detected a higher frequency of malaria infection (46%) in maternal peripheral blood in primiparous than in multiparous women (35%; P < 0.001), with a >12-fold difference in parasite burden (geometric mean = 25,870 versus 2,143 amplicons/μl blood; P < 0.0001). Similarly, the presence of placental malaria determined by RTQ-PCR was approximately twofold higher in primiparous versus multiparous women (21% versus 13%; P < 0.01). The presence and intensity of malaria infection in pregnant women estimated by RTQ-PCR strongly correlated with low-birth-weight babies, especially in those with high amplicon numbers. RTQ-PCR identified malaria-infected women, missed by blood smear, who were at risk for having underweight offspring. By contrast, malaria detected by nPCR and CAg assay showed a much weaker association with parity or low birth weight. Thus, RTQ-PCR provides an estimate of parasite burden that is more sensitive than blood smear and is predictive of clinical outcomes of malaria infection in pregnant women and newborns.

Influence of maternal filariasis on childhood infection and immunity to Wuchereria bancrofti in Kenya.

ABSTRACT To determine whether maternal filariasis influences the risk of infection by and immunity to Wuchereria bancrofti in children, we performed a cross-sectional study in an area of Kenya where filariasis is endemic. Residents of 211 households were enrolled; 376 parents and 938 of their offspring between the ages of 2 and 17 years were examined for filarial infection status as determined by blood-borne microfilariae and filarial antigenemia. Children of infected mothers had a three- to fourfold increased risk of filarial infection, as ascertained by circulating filarial antigen, relative to children of uninfected mothers (P < 0.001). Paternal infection did not correlate with childhood infection status, indicating a specific maternal effect. Peripheral blood mononuclear cells from children of filaria-infected mothers (n = 33) had higher levels of constitutive interleukin-5 (IL-5) and IL-10, increased microfilarial antigen-specific IL-5 production, and diminished microfilarial antigen-driven lymphocyte proliferation than cells from children of uninfected mothers (n = 46; P < 0.05). In contrast, there were no differences between the two groups in adult worm antigen-driven gamma interferon, IL-2, IL-4, IL-5, and IL-10 production and lymphocyte proliferation. These data indicate that maternal filarial infection increases childhood susceptibility to W. bancrofti and skews filaria-specific immunity toward a Th2-type cytokine response. The results support the notion that in utero exposure to filarial antigens affects the natural history of filariasis during childhood.

Umbilical Cord–Blood Infections with Plasmodium falciparum Malaria Are Acquired Antenatally in Kenya

BACKGROUND It is unknown whether the presence of Plasmodium falciparum malaria parasites in umbilical cord blood denotes infection acquired antenatally or contamination with infected maternal blood at delivery. METHODS Parasites were quantified by real-time quantitative polymerase chain reaction (RTQ-PCR) and were genotyped in paired maternal- and cord-blood samples obtained from 632 pregnant Kenyan women and their newborns. Placental alkaline phosphatase (PLAP) and polyclonal immunoglobulin E levels were also quantified in paired maternal- and cord-blood samples, as markers of admixture of maternal blood with cord blood. RESULTS Sixty-six cord-blood samples (10.4%) contained falciparum malaria, as detected by RTQ-PCR. For 25 of the infected cord-blood samples, either absence of infection was noted in paired maternal-blood samples at delivery (n=16) or amplicon levels in cord-blood samples were 10-fold higher than those in maternal-blood samples (n=9). Of the paired maternal- and cord-blood samples that were both infected, 57% showed discordant malaria parasite strains. There was no correlation between maternal parasitemia and levels of PLAP and immunoglobulin E in cord blood. PLAP levels, however, were significantly higher in cord-blood samples obtained from newborns of primigravid or secundigravid women with placental malaria, compared with cord-blood samples obtained from newborns of women without placental malaria or multigravid women. These findings indicate that parity and placental malaria are risk factors for maternofetal transfusion. CONCLUSIONS Malaria parasites identified in cord blood are acquired antenatally by transplacental transmission of infected erythrocytes. Primigravid and secundigravid women with placental malaria are at increased risk for congenital infection.