3HS0, 1DLE, 1Q0P, 1RRK, 1RS0, 1RTK, 2OK5, 2WIN, 2XWB, 2XWJ, 3HRZ62914962ENSG00000241534ENSG00000204359ENSMUSG00000090231P00751P04186NM_001710NM_001142706NM_008198NP_001701NP_001136178NP_032224NP_001389804Complement factor B is a protein that in humans is encoded by the CFB gene.

Upon activation of the alternative pathway, it is cleaved by complement factor D yielding the noncatalytic chain Ba and the catalytic subunit Bb.

The active subunit Bb is a serine protease that associates with C3b to form the alternative pathway C3 convertase.

This gene localizes to the major histocompatibility complex (MHC class III) region on chromosome 6.

This cluster includes several genes involved in regulation of the immune reaction.