Factor B deficiency

Factor B is a serine protease highly homologous to C2. The gene for factor B is part of the HLA class III region on chromosome 6. Factor B is a part of the alternate pathway which plays an important role in natural immunity. Factor B cleaves of C3 and C5 and is expressed primarily in hepatocytes and monocytic cells.

Alternative names

Complement factor B deficiency


  • Defects of the alternative complement pathway


Autosomal recessive


*138470 Properdin factor B; BF

Cross references

Phenotypically related immunodeficiencies

IDR factfile for C2 deficiency


Incidence is not known.