d. The data in Table 2-23 show that the cells of 66 percent of Whites and ten percent of
Blacks will react with anti-Fya, while cells of 85 percent of Whites and 23 percent of Blacks
react with anti-Fyb. Thus, the cells of almost all Whites react with both anti-Fy3 and anti-Fy5, and
68 percent of Black subjects (who are Fy (a-b-)) are nonreactive with these antibodies. About
96 percent of Blacks are Fy4-positive (based on the calculated frequency of the Fy or Fy4
gene) but virtually all Whites are Fy4-negative. Thus, finding compatible blood for
patients with Duffy system antibodies is greatly facilitated by searching for donors
among the appropriate ethnic group.
e. Recent reports strongly suggest that there is an association between the
Fy(a-b-) phenotype and resistance to malaria. Fy(a-b-) red blood cells have been
shown to be resistant to invasion "in vitro" with Plasmodium knowlesi. Of 17 volunteers
exposed to the bites of Plasmodium vivax-infected mosquitoes, only the five with the red
blood cell phenotype Fy(a-b-) were resistant to erythrocyte infection. It was concluded
that the Duffy determinants (Fya or Fyb or both) on the erythrocyte membrane are
required for invasion by vivax merozoites.
2-35. KIDD BLOOD GROUP SYSTEM
a. Anti-Kidd (Jka) was discovered in the serum of a woman who had given birth
to an infant with hemolytic disease of the newborn. It reacts with the blood of 77% of
Whites. Anti- Jkb reacts with the antithetical antigen. These two antibodies define the
four phenotypes listed in Table 2-25.
b. The phenotype Jk(a-b-) is very rare, and is apparently a result of a silent Jk
allele at the Kidd system locus. The serum of Jk(a-b-) individuals sometimes contains
an antibody that reacts with all Jk(a+) and Jk(b+) but not Jk(a-b-) cells. Like anti-Fy3,
the reaction does not seem to be caused by a mixture of antibodies, since it is not
possible to separate anti-Jka from anti-Jkb by absorption. It has been suggested that a
separate determinant, Jk3, is being detected.
Table 2-25. Phenotypes and frequencies in the Kidd system.