Complement factor B (CFB) is a circulating serine protease that plays a central role in the alternative pathway of the complement system, a critical component of innate immunity. Encoded by the CFB gene, this protein is primarily synthesized by hepatocytes, adipocytes, and monocytes, reflecting its systemic and local involvement in immune surveillance and inflammation ^[1]. Upon activation by factor D, CFB forms the active enzyme factor Bb, which, in complex with complement component C3b, constitutes the alternative pathway C3 convertase (C3bBb). This convertase catalyzes the cleavage of C3 into the anaphylatoxin C3a and the opsonin C3b, leading to the amplification of the complement cascade and the subsequent elimination of pathogens and damaged cells ^[2]. Dysregulation of CFB activity, often stemming from genetic polymorphisms within the CFB locus, has been implicated in the pathogenesis of several human diseases, including age-related macular degeneration (AMD), atypical hemolytic uremic syndrome (aHUS), and systemic lupus erythematosus (SLE), underscoring the delicate balance required for proper complement regulation and immune homeostasis ^[3-4]. These associations highlight CFB as a key mediator of both protective and pathological immune responses.

The B6-hCFB mouse is a humanized model constructed by replacing the sequence of the mouse Cfb gene in situ with the corresponding sequence from the human CFB gene. The homozygous B6-hCFB mice are viable and fertile and can be used for studies on age-related macular degeneration (AMD), atypical hemolytic uremic syndrome (aHUS), and systemic lupus erythematosus (SLE), and pathogenesis of immune-related diseases, as well as for CFB-targeted drug development.