In some holoendemic countries, individuals are bitten by malaria-infected mosquitoes 60-300 times a year [
1,
2]. The most common form of malaria in endemic countries is uncomplicated malaria, characterized by fever, chills, sweats, headaches and nausea. Cerebral malaria is a severe neurologic complication of
Plasmodium falciparum infection that occurs much less commonly than uncomplicated malaria. Genetic factors influence infection outcome, and polymorphisms in genes encoding proteins involved in disease pathogenesis are strong candidates for disease association studies. As a receptor for parasite derived GPI, TLR2 is likely involved in disease pathogenesis [
3], however, a previous study examining single nucleotide polymorphisms (SNPs) within TLR2 could not detect an association with severe disease because these SNPs were absent in the populations studied [
4]. Reportedly, TLR2 SNPs are absent in some African countries as well, but insertion deletion polymorphisms within the 5' un-translated region of TLR2 are very common [
5,
6]. A 22 bp insertion/deletion polymorphism (
TLR2 Δ22) in the first un-translated exon was highly polymorphic in Kenyans and in a Japanese population but was not associated with a disease phenotype [
5,
7]. A GT dinucleotide repeat that varies by approximately 12 to 30 repeats (GT
n) is present within the second intron, approximately 100 bp upstream of the translational start site. Repeats of varying length have been associated with susceptibility to tuberculosis, reversal reactions in leprosy and colorectal cancer [
8‐
10]. These polymorphisms are associated with altered in vitro phenotypes. The TLR2 Δ22 polymorphism was associated with reduced constitutive luciferase reporter activity compared to a construct containing the insertion allele [
7]. Shorter GT
n repeats are associated with reduced TLR2 reporter activity and TLR2 surface expression in vitro [
8]. Altered TLR2 expression in individuals with different TLR2 polymorphisms may lead to differential pro-inflammatory responses based on genotype. TLR2 expression on human monocytes ex vivo is highly variable [
11]. Reports on pam3cys and LPS inducible TLR2 expression on human monocytes vary, likely due to donor specific differences as monocytes differentiate into macrophages [
11,
12].
Plasmodium falciparum derived GPI activate TLR2 to induce TNF, IL-12, IL-6 and nitric oxide in murine bone marrow derived macrophages [
3]. Elevated levels of IFN-γ, TNF, IL-12, IL-6, IL-1β, and IL-10 are initially protective, although excessive serum levels of these cytokines are associated with cerebral malaria pathology [
13‐
15]. Similarly, IFN-γ and TNF are necessary for disease in the murine model of cerebral malaria [
16‐
19]. In the children examined in this study, cerebral malaria patients had elevated serum levels of IFN-γ, IL-1β, and IL-10 compared to uncomplicated malaria patients [
20]. Although neither IL-6 nor TNF serum levels were correlated with severe disease in these children [
20] these cytokines are often associated with severe disease in other epidemiologic studies [
13].
In the current study, the role of TLR2 insertion/deletion polymorphisms, Δ22 and GTn, in the pathogenesis of cerebral malaria was evaluated. Genomic DNA and serum were collected from Ugandan children participating in a case control study examining children with cerebral malaria and uncomplicated malaria. This data indicates heterozygosity for Δ22 polymorphism was protective (odds ratio 0.34, 95% CI 0.16-0.73), but there was no disease association with the GTn polymorphism. In malaria naïve donors, Δ22 heterozygosity was associated with reduced pam3cys induced TLR2 stimulation in human monocyte derived macrophages. In Ugandan children involved in the case control study, none of these polymorphisms was associated with serum cytokines in the cerebral malaria group. In the uncomplicated malaria group, homozygosity for the Δ22 insertion allele was associated with elevated IL-6 (p = 0.04), and at least one long GT repeat allele was associated with elevated serum TNF levels (p = 0.007). This data suggests that the TLR2 insertion deletion polymorphisms may be involved in cerebral malaria pathogenesis through alteration of induced TLR2 expression and down-regulation of specific pro-inflammatory cytokines.