ICAM4
| Intercellular Adhesion Molecule-4 (Landsteiner-Wiener blood group system) | |||||||
|---|---|---|---|---|---|---|---|
| Identifiers | |||||||
| Symbol | ICAM-4 | ||||||
| Alt. symbols | LW | ||||||
Chr. 19 p13.2-cen | |||||||
| |||||||
The LW blood system was first described by
Rh system, not becoming a separate antigen system until 1982. The LW and RhD antigens are genetically independent though they are phenotypically related and the LW antigen is expressed more strongly on RhD positive cells than on RhD negative cells. In most populations, the antithetical LW antigens, LWa and LWb are present as very high and very low frequency, respectively.[1][2][3]
Genomics
The LW locus is located on the short arm of chromosome 19 (19p13.3).[1]
Molecular biology
LW antigens reside on a 40- to 42-kilo
integrins
bind to ICAM-4 is subject to controversy.
The function of ICAM-4 is not fully understood but appears to be restricted to
αv integrins on macrophages to help stabilise the erythroblastic islands. The binding of red cells to macrophages in the spleen by ICAM-4 could also play a part in the removal of senescent red cells.[1][2][3]
Despite the functional aspects of ICAM-4, its apparent absence in LW(a-b-) and Rhnull phenotypes does not appear to lead to any obvious pathological effects. ICAM-4 expression is elevated on sickle red cells and its binding to αv integrins on the endothelial cells may cause the pain associated with
Auto anti-LW is not uncommon as an
autoimmune haemolytic anaemia; Philip Levine suggested that it was the most common antibody in cases of AIHA with a positive Coombs test.[1][4][5]
Transfusion medicine
Haemolytic disease of the newborn (HDFN) due to alloanti-LW is described as mild and very rare, even the very potent anti-LWab of one known patient caused minimal evidence of HDFN in her three pregnancies.[6] To date auto anti-LW has only been implicated as the cause of one case of HDFN.[7]