Which of the following correctly explains why sickle cell trait (HbAS) confers protection against falciparum malaria?

• A HbS polymerizes under low oxygen, causing sickling and expulsion of parasites
• B HbS directly kills the Plasmodium merozoite
• C HbAS cells have reduced surface DARC receptors that Plasmodium vivax uses for invasion
• D Infected HbAS cells sickle under the low-oxygen conditions in parasitized cells, leading to phagocytic clearance before parasite replication ✓

Explanation

In HbAS heterozygotes, parasitized red cells experience reduced intracellular pH and oxygen tension during falciparum infection, causing HbS polymerization in these specific cells. This leads to their preferential phagocytosis by macrophages before the parasite completes its cycle, thereby reducing parasitemia and severe disease. The protective mechanism operates mainly during parasitized-cell sickling, not indiscriminate sickling.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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