In 1965 McCormick, Francis and Gelb described an antibody in the serum of an
African-American prenatal patient. Since the patient's red cells typed as Go(a+) they
believed the antibody was anti-Gob. However, ten years later
Stroup and McCreary reported four additional examples of the antibody and demonstrated
that it could not be part of the Rh system and was not anti-Gob.
Thus the antibody was renamed anti-Cromer (Cra) after the first
antibody producer. To date, the majority of these antibodies have been found in Blacks and
are often stimulated by pregnancy.
Additional antigens and antibodies were soon discovered for this system, some of
which showed distinct ethnic differences. The antibody to the high frequency antigen known
as Tca was first found in two Black females. Indeed, its low
frequency partner was found in 5% of Blacks but not in Caucasians. In the later group,
another low incidence partner was found which was named Tcc. A
new antibody related to Cromer was reported by Levene and named anti-Dra.
Several examples of Dr(a-) have been found almost exclusively in Israeli Jews originating
from the Bukharan area of Uzbekistan.
The biochemical structure and functional significance of the Cromer blood group came to
light when it was shown that these antigens are carried on a protein known as "decay
accelerating factor" (DAF). The DAF protein was well known to scientists studying
complement, ie. a group of proteins important in inflammation. DAF is a regulatory protein
which controls several of the complement components known as the C3 convertase. Today, all
of the different Cromer/DAF genes have been cloned and the exact mutations identified.
Cra is due to a G-C change in SCR4 leading to an ala193pro
substitution. Most of the other Cromer system antigens have been found in SCR1 at the DAF
Individuals who acquire a deficiency of DAF on their red blood cells develop an anemia
known as paroxysmal nocturnal hemoglobinuria (PNH). However, extremely rare individuals
have an inherited form of DAF deficiency. This is know as the "Inab" phenotype
and these red cells lack all of the Cromer blood group antigens as well as the DAF
protein. Interestingly, the Dra antigens carried on DAF play a unique role in
the binding of a bacteria, ie. Escherichia coli, to the lining of the urinary
tract. It appears that the bacteria uses the DAF protein for attachment to the cell lining
in order to establish infection.