Early studies showed that the donor and recipient genotypes in genes that regulate the host response to microorganisms, including myeloperoxidase (MPO), mannose binding lectin (MBL) and Fcγ receptors (FcγRIIa, IIIa, IIIb), were reportedly associated with infections after BMT (Rocha et al., 2002). This evidence concerns the gene MBL2 and infection.