Background
Malaria resistance by the sickle cell trait (genotype HbAS) has served as the prime example of genetic
selection for over half a century. Nevertheless, the mechanism of this resistance remains the subject of considerable debate. While it probably involves innate factors such as the reduced ability of Plasmodium falciparum parasites to grow and multiply in HbAS erythrocytes, recent
observations suggest that it might also involve the accelerated acquisition of malaria-specific immunity.
Methods and Findings
We studied the age-specific
protection afforded by HbAS against clinical malaria in children living on the coast of Kenya. We found that protection increased with age from only 20 in the first 2 y of life to a maximum of 56 by the age of 10 y, returning thereafter to 30 in participants greater than 10 y old.
Conclusions
Our observations suggest that malaria protection by HbAS involves the enhancement of not only innate but also of acquired immunity to the parasite. A better understanding of the underlying mechanisms might yield important insights into both these processes.