Association between Natural Cytotoxicity Triggering Receptor- 3 Polymorphisms (-172a/G and -412c/G) and Interferon-Gamma Levels in Children Aged 3-36 Months with Severe Plasmodium Falciparum Anaemia at Siaya County Referral Hospital in Western Kenya

Abstract

In sub-Saharan Africa, Plasmodium falciparum infection is a major cause of morbidity and mortality mostly among children under five years. In Kenya, severe malaria anaemia prevalence is at 19%. In malaria holo-endemic region of western Kenya, P. falciparum infections account for major proportion of children with anaemia that leads to severe malaria anaemia (SMA, Hb<6.0g/dL with any parasite density). Children in these areas exhibit similar transmission intensity and infection rates of P. falciparum malaria with different malaria outcomes. The reason(s) for these varied clinical outcomes is poorly defined. Natural Cytotoxicity Triggering Receptor 3 directly interacts with Duffy binding-like-1 alpha (DBL-1α) peptides on parasitized red blood cells (PRBCs) thus activating natural killer cells to carry out cell-mediated cytotoxicity of Pf. PRBCs releasing interferon gamma (IFN-γ), a major cytokine that activates phagocytes during malarial infection. In particular, NCR3 plays important role in pathogen recognition. Previous studies associated NCR3 with pathogenesis of different infectious diseases, P. falciparum malaria included. However, the association between polymorphic variants of NCR3 promoter and pathogenesis of SMA and peripheral-IFN-γ levels especially in paediatric populations exposed to P. falciparum in holoendemic transmission regions such as western Kenya has not been reported. As such, this case-control study, investigated the association between NCR3 polymorphisms, susceptibility to SMA and IFN-γ levels; Specifically, the study determined the association between NCR3 -172A/G (rs986475) and NCR3 -412C/G (rs2736191) polymorphic variants and susceptibility to SMA; association between NCR3 -172A/G (rs2736191) and NCR3 -412C/G (rs986475) genotypes/haplotypes and IFN-γ levels and comparision of IFN-γ levels in children (n=455) aged below 3 years with SMA cases (n=254) and without SMA, controls (n=201) were targeted at Siaya County Referral Hospital (SCRH) of western Kenya. Prior to administration of any medication, haematological and parasitological parameters were determined in all the participants. NCR3 (-172A/G and -412C/G) genotypes were determined using TaqMan high throughput assays while IFN- levels were determined using cytokine 25-plex Ab Bead Kit. Bivariate logistic regression analysis controlling for confounding factors such as age, HIV-1, bacteraemia, α-thalassemia and sickle-cell trait revealed that children with NCR3 -172G/-412C haplotype carriage were nearly five times at an increased risks of developing SMA (OR; 4.977, 95% CI, 1.494-16.580, P = 0.009), while carriers of NCR3 -172A/-412C and NCR3 -172G/-412G haplotypes did not alter susceptibility to SMA (OR; 0.133, 95% CI, 0.011-1.610, P = 0.113) and (OR; 0.543, 95% CI, 0.227-1.300, P = 0.171), respectively. Children with NCR3 -172G/-412C haplotye carriage showed significant difference in peripheal IFN-γ levels (P< 0.0001). Carriage of the genotype GG relative to genotype AG showed significant differences in IFN-γ levels (P=0.006). There were no significant difference in peripheral IFN-γ levels between SMA and non-SMA (P=0.173). Collectively, these results demonstrate that haplotypes of NCR3 are important in conditioning susceptibility to SMA pathogenesis and changes in the peripheral IFN-γ levels in immune-naïve children naturally exposed to P. falciparum infection. These findings on the role of NCR3 receptors in SMA pathogenesis may be used in informing crucial decisions for designing and developing therapeutics for children in P. falciparum holoendemic region of western Kenya.