c. It is difficult to work with the treacherous antibodies of the Kidd system. They
are often weak when first detected and, because of complement-dependence, may
become undetectable in stored serum. When a fresh serum contains Kidd antibodies,
the antiglobulin serums used for their detection should contain optimum levels of
anti-complement. Older serums may require addition of fresh complement. Added to
these difficulties, the production of Kidd antibodies is evanescent (transient, tending to
vanish) and they are frequently accompanied by other blood group antibodies as well.
d. Antibodies of this system are well-known for causing severe transfusion
reactions and delayed transfusion reactions. These evanescent antibodies may be
undetectable at the time of cross-matching but may attain considerable levels at the
time of transfusion. Hemolytic disease of the newborn caused by these antibodies is
distinctly rare (see Table 2-26).
Table 2-26. Serologic behavior of Kidd system antibodies.
2-36. MNSs BLOOD GROUP SYSTEM
a. The M and N antigens behave in most respects like the products of a pair of
allelic genes: the red cells of persons lacking an M gene type as M-N+; those with one
M gene type as M+N+; and individuals homozygous for M type as M+N-.
b. M and N antigens show a marked dosage effect. Thus MM and NN cells
often react much stronger with anti-M and -N, respectively, than MN cells.
c. There is strong evidence at a complex biochemical pathway is involved in
which N represents an intermediate product in the production of M. Individuals of
phenotype M+N- can be shown, by sensitive tests, to possess some N antigen.
d. The antigens S and s appear to be produced by another pair of allelic genes
closely linked to the MN locus. The gene (or gene complex) producing M and s is more
common than the one producing M and S. The complex producing N and s is 5 times
more common than the one producing N and S. Most genes (or gene complexes) that
cause the production of S or s also cause the production of a high-incidence antigen in
this system called U. Some Black individuals have cells which are S-, s-, and U-, while
others are S-, s-, U+, showing that anti-U is not anti-Ss in an inseparable form (see