C4B deficiency is not associated with meningitis or bacteremia with encapsulated bacteria.

The two isotypes of the fourth complement component are C4A and C4B. C4B forms ester bonds more efficiently than C4A and so, in theory, is more likely than C4A to bind to polysaccharide capsules of encapsulated bacteria. Two studies have reported homozygous C4B deficiency in patients with meningitis or bacteremia caused by encapsulated organisms. In the present study the association between C4B deficiency and these disorders was evaluated in four groups: patients with bacteremia, those with meningitis, those who developed Haemophilus influenzae type b (Hib) disease after Hib polysaccharide vaccination, and patients less than 1 year old with meningitis. Healthy adults served as controls. Of the 257 patients, 2.3% had homozygous C4B deficiency compared with 3.7% of 349 controls. According to these data, there is no increase in homozygous C4B deficiency among patients with bacteremia or meningitis caused by encapsulated bacteria.