Serum C3 content in vitamin B₁₂-deficient rats

As a clue to clarifying the role of vitamin B₁₂ (B₁₂) in the function of the complement system, serum C3 content was determined in B₁₂-deficient rats, and the effect of the administration of methylcobalamin (CH₃-B₁₂) on the serum C3 content was also studied. It was found that the serum C3 content in rats fed on a vitamin B₁₂-deficient diet for 90 and 120 days significantly decreased compared with that in control rats. The administration of CH₃-B₁₂ restored the serum C3 content to control levels. The above results indicate that B₁₂-deficiency depressed the serum C3 content and lowered humoral immunocompetence, and that these changes were ascribable to B₁₂-deficiency.