Genetic variation in Plasmodium falciparum CX3CL1-binding protein genes and their association with severe malaria in Thailand

Background Plasmodium falciparum CX3CL1 binding proteins, CBP1 and CBP2, specifically bind to chemokine CX3CL1 on endothelial cells, mediating endothelial cytoadherence. They are also involved in host-cell remodeling, parasite protein trafficking, and gametocyte survival. Given their plausible role in parasite biology and host–parasite interactions, this study analyzed genetic variation in cbp1 and cbp2 and examined their association with malaria severity in Thai patients. Methods Gene analysis of cbp1 and cbp2 was performed in 473 P. falciparum isolates from Thai patients, who presented with mild symptoms, cerebral malaria, or severe malaria without cerebral complications. The full lengths of cbp1 and cbp2 from 30 P. falciparum isolates were sequenced to screen for polymorphisms using Illumina-based sequencing. Single-nucleotide polymorphisms (SNPs) were analyzed in all samples by polymerase chain reaction–restriction fragment length polymorphism and Sanger sequencing. The association between gene polymorphisms and malaria outcomes was examined. Results Nine SNPs and 5 microsatellites were identified in cbp1 . Three synonymous SNPs were in exon 2, while others were found in non-coding regions. For cbp2 , 3 non-coding SNPs and 9 microsatellites were detected, but no variations in coding sequences were noted. Significant associations were found between cbp1 379 C/T in the intron near the splicing site and cerebral malaria (odds ratio [OR] 1.99, 95% confidence interval [CI] 1.03–3.85), as well as between cbp2 2306 A/T in the 3ʹ untranslated region (UTR) and severe malaria (without cerebral complications); OR 6.67, 95% CI 1.28–34.73). Parasite density did not differ significantly between the cbp1 and cbp2 genotypes. Conclusions The high degree of genetic conservation in P. falciparum cbp1 and cbp2 was observed among clinical isolates. Two variants, 379C/T in the intron near the splicing site of cbp1 and 2306A/T in the 3ʹ UTR of cbp2 , showed a modest association with malaria severity. Further functional studies are warranted to elucidate the biological basis underlying this apparent association.