Not to be confused with Lutheran or Lewis, Anti-LW antibodies, named after Karl Landsteiner and Alexander Wiener, are generally thought to be nuisance antibodies in the transfusion medicine world, with little impact on clinical outcomes to patients in regard to transfusion and Red Cell survival. However, their true identification is important for certain populations of people, such as pregnant women.
Anti-LW antibodies often manifest with an Anti-D pattern on antibody screen / panels. The reason for this is that LW glycoproteins are expressed at an increased rate on Rh positive Red Blood Cells. It is posited that the LW glycoprotein actually requires interaction with the Rh proteins to properly express itself on the Red Blood Cell. Thus Rh negative cells express little to no LW glycoprotein. As a result, RhD positive cells will usually react much stronger with an Anti-LW antibody. RhD negative cells will usually react much weaker or not at all depending on LW expression. So we can see that, even though LW and RhD antigens are not related from a genetic standpoint, they are phenotypically related in that they may produce apparent Anti-D reactivity.
The LW blood group system (also potentially known as ICAM4 or Intercellular Adhesion Molecule-4) consists of 3 known antigens -- LWa, LW(b), and LWab. LWa is extremely common (greater than 90% of most populations). LWb is a low frequency antigen, and LWab even less.
Most anti-LW antibodies are IgG in nature and generally exist as an autoantibody. They are not known to activate compliment. Allo-Anti-LW is extremely rare but has been known to occur in only a few patients, those who are Lwa(-)Lwb(-) are most at risk of developing an alloantibody.
Anti-Lw antibodies are often seen in certain populations where expression of Lw antigens is transiently suppressed. Some pregnant women and those with certain hematologic malignancies may suppress their Lw expression, this can cause a temporary Anti-Lw(a) or Anti-Lw(ab) to be produced. It has been observed that the antibody reactivity clears up once pregnancy or disease state has passed.
Allo Anti-Lw has been implicated in a single known potential instance of HDFN, which was relatively mild. Cases of autoanti-Lw do not result in hemolytic transfusion reactions. However, to obtain a compatible crossmatch, it may be necessary to transfuse Rh negative blood, given Lw expression is lower on Rh negative cells. Transfusion of RhD positive cells likely would not result in hemolysis or decreased RBC survival, but each transfusion center will have its own rules on how it deals with Anti-Lw transfusion.
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