h. Since glycosphingolipids with Lewis antigenic activity are poorly developed at
birth, and since antibodies of the IgM class do not cross the placenta, neither anti-Lea
nor anti-Leb causes hemolytic disease of the newborn. Since Lewis antibodies are
readily neutralized by Lewis blood group substances present in plasma, and Lewis-
positive red blood cells lose their Lewis antigens when transfused into Lewis-negative
recipients, "in vivo" reactions, are rare. No hemolytic transfusion reactions have been
proven to be caused by anti-Leb, but anti-Lea has been implicated. Le(a-) blood is easily
found for patients having anti-Lea present in their serum. To obtain blood for a patient
with anti-Leb, some workers have neutralized Lewis antibodies successfully "in vivo" by
transfusing plasma containing Lewis blood-group substances before carrying out
compatibility-testing and transfusion of Lewis-positive blood, however, for most
recipients, it is quite acceptable to use Le(a-b+) blood for transfusing, since anti-Leb is
so rarely capable of red blood cell destruction.
2-31. I BLOOD GROUP SYSTEM
a. The I system differs from most of the other blood group systems in several
ways. Fetal red cells are rich in an antigen known as i and have very poorly developed I
antigen. At birth, the I antigen is still poorly developed but there is a gradual
development of I antigen and a loss of i antigen during the first 2 years; thus, the normal
adult's red blood cells react strongly with anti-I but weakly with anti-i. The strength of I
antigen varies considerably among normal adults. Rare adults exist who have even
less I antigen and more i antigen on their red blood cells than cord red blood cells, the
so-called i(adult). No cells completely lack either the I or i antigens. In some conditions
associated with bone marrow stress (for example, thalassemia, congenital dyserythropoietic
anemia, and so forth), adults may have greatly increased i antigen on their red blood cells
without a concomitant decrease of I antigen.
b. An antibody whose reaction is strong against cord cells, weaker against adult
cells and, in contrast to anti-i, weaker still against the rare i (adult) phenotype, has been
described. It was suggested that the antigen it detected, IT, was transitional between i
and I. Table 2-16 shows the relative amounts of these antigens on various red blood
cells.
Table 2-16. Amounts of I system antigens on different red blood cells.
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