ABCB1 and osteonecrosis: Another example is that the T/T genotypes from the C1236T and C3435T polymorphisms of the gene encoding the adenosine triphosphate (ATP)-binding cassette subfamily B member 1 (ABCB1) show protective roles against osteonecrosis as compared with the wildtype (C/C) genotypes, where ABCB1 functions by pumping foreign substances out of cells and is lowly expressed among SLE patients.406–408 In summary, reduced level of ABCB1 is associated with cells’ decreased ability of removing immune stimulants and consequently increased SLE activity and elevated risk of developing osteonecrosis.