The Role of Complement in Antibody-Dependent Acquired Immunity to <i>Plasmodium falciparum</i> Malaria

Many pathogens evade complement recognition by binding to complement regulatory proteins, such as factor H (FH), that protect host cells from complement attack. Asexual Plasmodium falciparum stages evade complement destruction by capturing FH on their surface. An initial study identified Pf92 as the only protein that interacts with FH; however, the Pf92 knockout transgenic parasites did not wholly abolish FH recruitment to the merozoite. Thus, I hypothesized that potentially, more merozoite proteins are involved in complement evasion. I used a combination of modified ELISA binding assay and surface plasmon resonance and tested a library of 110 recombinant merozoite proteins for interaction with FH. Protein microarray was used to measure antibody responses to the merozoite antigens that interacted with FH in a malaria longitudinal cohort of children. Additionally, I tested whether circulating levels of FH and the Y402H variant in the FH gene influence malaria severity. In addition to Pf92, I found seven additional merozoite proteins that interact with the FH, i.e. PF3D7_1105800, PF3D7_0206200, RH5, P12, PF3D7_1252300, PF3D7_0629500 (SEG) and P12p. Majority of the proteins bound to complement control protein modules (CCP) 5-7 of FH. Antibody responses against a combination of some of these merozoite FH receptor antigens were found to be associated with protective immunity. Children with severe malaria (SM) had markedly lower circulating FH levels compared to uncomplicated malaria (UM) controls (median: SM=269 ug/ml, UM=378 ug/ml, P=P=0.195) when compared with normal individuals. These findings suggest that the Plasmodium falciparum parasite uses many proteins to interact with FH to avoid complement destruction and that FH protein, could be a vital host determinant for malaria severity. This study offers insights into the mechanisms of malaria parasite complement immune evasion and provides a rationale for future studies to evaluate stage-specific parasite proteins for interaction with complement regulatory proteins

Quantifying maternally derived respiratory syncytial virus specific neutralising antibodies in a birth cohort from coastal Kenya.

BACKGROUND: Severe respiratory syncytial virus (RSV) disease occurs predominantly in children under 6 months of age. There is no licensed RSV vaccine. Protection of young infants could be achieved by a maternal vaccine to boost titres of passively transferred protective antibodies. Data on the level and kinetics of functional RSV-specific antibody at birth and over the early infant period would inform vaccine product design. METHODS: From a birth cohort study (2002-2007) in Kilifi, Kenya, 100 participants were randomly selected for whom cord blood and 2 subsequent 3-monthly blood samples within the first year of life, were available. RSV antibodies against the A2 strain of RSV were assayed and recorded as the logarithm (base 2) plaque reduction neutralisation test (PRNT) titre. Analysis by linear regression accounted for within-person clustering. RESULTS: The geometric mean neutralisation antibody titre was 10.6 (SD: 1.13) at birth with a log-linear decay over the first 6 months of life. The estimated rate of decay was -0.58 (SD: 0.20) log2PRNT titre per month and a half-life of 36 days. There was no significant interaction between cord titre and rate of decay with age. Mean cord titres rose and fell in a pattern temporally tracking community virus transmission. CONCLUSIONS: In this study population, RSV neutralising antibody titres decay approximately two-fold every one month. The rate of decay varies widely by individual but is not related to titre at birth. RSV specific cord titres vary seasonally, presumably due to maternal boosting

Agreement between ELISA and plaque reduction neutralisation assay in Detection of respiratory syncytial virus specific antibodies in a birth Cohort from Kilifi, coastal Kenya.

Background: Severe disease associated with respiratory syncytial virus (RSV) infection occurs predominantly among infants under 6 months of age. Vaccines for prevention are in clinical development. Assessment of the vaccine effectiveness in large epidemiological studies requires serological assays which are rapid, economical and standardised between laboratories. The objective of this study was to assess the agreement between two enzyme linked immunosorbent assays (ELISA) and the plaque reduction neutralisation test (PRNT) in quantifying RSV specific antibodies. Methods: Archived sera from 99 participants of the Kilifi Birth Cohort (KBC) study (conducted 2002-2007) were screened for RSV antibodies using 3 methods: ELISA using crude RSV lysate as antigen, a commercial RSV immunoglobulin G (IgG) ELISA kit from IBL International GmbH, and PRNT. Pearson correlation, Bland-Altman plots and regression methods were used in analysis. Results: There was high positive correlation between the IBL RSV IgG ELISA and PRNT antibodies (Pearson r=0.75), and moderate positive correlation between the crude RSV lysate IgG ELISA and PRNT antibodies (r= 0.61). Crude RSV lysate IgG ELISA showed a wider 95% limit of agreement (-1.866, 6.157) with PRNT compared to the IBL RSV IgG ELISA (1.392, 7.595). Mean PRNT titres were estimated within a width of 4.8 log 2PRNT and 5.6 log 2PRNT at 95% prediction interval by IBL RSV IgG and crude RSV lysate IgG ELISA, respectively. Conclusion: Although, the IBL RSV IgG ELISA is observed to provide a reasonable correlate for PRNT assay in detecting RSV specific antibodies, it does not provide an accurate prediction for neutralizing antibody levels. An RSV neutralising antibody level is likely to fall within 2.4 fold higher and 2.4 fold lower than the true value if IBL RSV IgG ELISA is used to replace PRNT assay. The utility of an ELISA assay in vaccine studies should be assessed independent of the PRNT method

An Intensive, Active Surveillance Reveals Continuous Invasion and High Diversity of Rhinovirus in Households.

We report on infection patterns in 5 households (78 participants) delineating the natural history of human rhinovirus (HRV). Nasopharyngeal collections were obtained every 3-4 days irrespective of symptoms, over a 6-month period, with molecular screening for HRV and typing by sequencing VP4/VP2 junction. Overall, 311/3468 (8.9%) collections were HRV positive: 256 were classified into 3 species: 104 (40.6%) HRV-A; 14 (5.5%) HRV-B, and 138 (53.9%) HRV-C. Twenty-six known HRV types (13 HRV-A, 3 HRV-B, and 10 HRV-C) were identified (A75, C1, and C35 being most frequent). We observed continuous invasion and temporal clustering of HRV types in households (range 5-13 over 6 months). Intrahousehold transmission was independent of clinical status but influenced by age. Most (89.0%) of HRV infection episodes were limited to <14 days. Individual repeat infections were frequent (range 1-7 over 6 months), decreasing with age, and almost invariably heterotypic, indicative of lasting type-specific immunity and low cross-type protection

Human Coronavirus NL63 Molecular Epidemiology and Evolutionary Patterns in Rural Coastal Kenya.

Background: Human coronavirus NL63 (HCoV-NL63) is a globally endemic pathogen causing mild and severe respiratory tract infections with reinfections occurring repeatedly throughout a lifetime. Methods: Nasal samples were collected in coastal Kenya through community-based and hospital-based surveillance. HCoV-NL63 was detected with multiplex real-time reverse transcription PCR, and positive samples were targeted for nucleotide sequencing of the spike (S) protein. Additionally, paired samples from 25 individuals with evidence of repeat HCoV-NL63 infection were selected for whole-genome virus sequencing. Results: HCoV-NL63 was detected in 1.3% (75/5573) of child pneumonia admissions. Two HCoV-NL63 genotypes circulated in Kilifi between 2008 and 2014. Full genome sequences formed a monophyletic clade closely related to contemporary HCoV-NL63 from other global locations. An unexpected pattern of repeat infections was observed with some individuals showing higher viral titers during their second infection. Similar patterns for 2 other endemic coronaviruses, HCoV-229E and HCoV-OC43, were observed. Repeat infections by HCoV-NL63 were not accompanied by detectable genotype switching. Conclusions: In this coastal Kenya setting, HCoV-NL63 exhibited low prevalence in hospital pediatric pneumonia admissions. Clade persistence with low genetic diversity suggest limited immune selection, and absence of detectable clade switching in reinfections indicates initial exposure was insufficient to elicit a protective immune response

Replication Data for: Human Coronavirus NL63 Molecular Epidemiology and Evolutionary Patterns in Rural Coastal Kenya

This dataset contains demographic and laboratory results of human corona virus for samples collected in a household survey study in rural coastal Kenya. Data was collected in December 2009 to June 2010

Human coronavirus NL63 molecular epidemiology and evolutionary patterns in rural coastal Kenya

Background: Human coronavirus NL63 (HCoV-NL63) is a globally endemic pathogen causing mild and severe respiratory tract infections with reinfections occurring repeatedly throughout a lifetime. Methods: Nasal samples were collected in coastal Kenya through community-based and hospital-based surveillance. HCoV-NL63 was detected with multiplex real-time reverse transcription PCR, and positive samples were targeted for nucleotide sequencing of the spike (S) protein. Additionally, paired samples from 25 individuals with evidence of repeat HCoV-NL63 infection were selected for whole-genome virus sequencing. Results: HCoV-NL63 was detected in 1.3% (75/5573) of child pneumonia admissions. Two HCoV-NL63 genotypes circulated in Kilifi between 2008 and 2014. Full genome sequences formed a monophyletic clade closely related to contemporary HCoV-NL63 from other global locations. An unexpected pattern of repeat infections was observed with some individuals showing higher viral titers during their second infection. Similar patterns for 2 other endemic coronaviruses, HCoV-229E and HCoV-OC43, were observed. Repeat infections by HCoV-NL63 were not accompanied by detectable genotype switching. Conclusions: In this coastal Kenya setting, HCoV-NL63 exhibited low prevalence in hospital pediatric pneumonia admissions. Clade persistence with low genetic diversity suggest limited immune selection, and absence of detectable clade switching in reinfections indicates initial exposure was insufficient to elicit a protective immune response

Relationship between Odds of RSV disease and the levels of Cord blood antibody titres.

<p>A scatter plot showing the odds of RSV associated hospitalization against maternally transferred RSV specific antibodies (log₂PRNT titres) from cord blood samples of infants (both cases and controls) born in Kilifi, Kenya; 2002–2007. Black symbols denote individual cord titres for all 90 infants.</p

Characteristics of study participants.

<p>Characteristics of study participants.</p