Which statement about the complement system is NOT true?

• A. It can be activated by antibodies
• B. It shows dosage effect with homozygous cells
• C. It is a group of at least 9 plasma proteins
• D. It participates in inflammation

Answer: (B)

Understanding how the complement system works helps explain why the statement about dosage effects is not accurate. The complement system is a cascade of at least nine plasma proteins that can be activated to fight infections and promote inflammation. It can be triggered by antibodies through the classical pathway or by direct microbial surfaces via the alternative pathway, and its activation products (like C3a and C5a) drive inflammation and opsonization.

The idea of a dosage effect with homozygous cells doesn’t fit how complement functions. Complement activity depends on the availability and activation of its protein components and on triggers such as antibody-antigen complexes or microbial surfaces, not on the zygosity of cells. Dosage effects are a concept used to describe how certain antigens on red blood cells are expressed more or less strongly depending on genetics, which is separate from how the complement cascade operates.