The monoclonal antibody 2D5B6 reacts specifically with human MAp-44, a protein of approximately 44kDa, which is encoded by an alternatively spliced mRNA of the MASP-1 gene. Up to now 5MASP proteinshave been identified (MASP-1, MASP-2, MASP-3, MAp19 and MAp44) which are encoded by 2 genes. The MASP-2 gene gives rise to MASP2 and MAp19 due to alternative splicing, whereas the MASP-1 gene encodes a primary transcript which can be spliced to three different mRNAs coding for MASP-1, MASP-3 and MAp44. On the protein level MASP-1 and MASP-2 are shown to be responsible for complement activation through proteolytic cleavage of C2 and C4, whereas MASP-3 has been suggested to inhibit the generation of the C3 convertase.So far the role of MAp44 remains elusive. However, recent research have shown that patients suffering from colorectal cancer have increased levels of MAp44 upon surgery as compared to Map44 levels in normal sera. The monoclonal antibody 2D5B6 is suitable for immunohistochemistry, western blotting as well as use in immunoassays.