**Question:** Duffy blood group antigen negativity confers protection against infection by: September 2012

**Core Concept:** The Duffy blood group antigen is a protein found on the surface of red blood cells. There are two types of Duffy antigens: Fy(a+) and Fy(a-b-). The Fy(a-) phenotype (absence of Duffy antigen) is associated with a reduced risk of certain infections.

**Why the Correct Answer is Right:** Duffy antigen is recognized by Plasmodium vivax and P. ovale malaria parasites during their invasion of red blood cells. Specifically, the Duffy antigen serves as a receptor for the parasite's invasion. When individuals with the Fy(a-) phenotype lack this receptor, the parasites are unable to invade their red blood cells, leading to reduced risk of infection.

**Why Each Wrong Option is Incorrect:**

A. This option is incorrect because Plasmodium vivax and P. ovale malaria parasites specifically target Fy(a+) individuals for invasion, not those with the Fy(a-) phenotype.

B. This option is incorrect because Duffy-negative individuals are still at risk for other types of malaria, such as Plasmodium falciparum which does not rely on Duffy antigen for invasion.

C. This option is incorrect because Duffy-negative individuals are still at risk for infections other than malaria, such as those that do not involve the Fy(a+) receptor.

D. This option is incorrect because the protection provided by Duffy antigen negativity is not solely due to reduced risk of malaria, but also other infections that involve the Fy(a+) receptor.

**Clinical Pearl:** Duffy antigen negativity provides protection against Plasmodium vivax and Plasmodium ovale malaria infections. However, it does not entirely eliminate the risk of infections involving the Fy(a+) receptor.

**Correct Answer:** D. Duffy antigen negativity provides protection against Plasmodium vivax and Plasmodium ovale malaria infections, and also reduces the risk of other infections involving the Fy(a+) receptor.