Gm allotypes influence the production of IgG3 but the effect is age-dependent. 
Serum concentrations of IgG3 were found to be higher in Gm-f-positive (= b-positive) than in f-negative individuals except in young children.  Young children aged 3-4 months had a mean concentration of 0.24 g/l of IgG3 regardless of allotype.  The concentration gradually rose with age in f-positive individuals to a geometric mean of 0.56 g/l in adults but it remained essentially unchanged in f-negative people.  A corresponding allotype effect was seen in influenza-specific antibody responses.  While the total IgG response (mainly IgG1) was equally strong in f-positive and in f-negative patients, f-positive (= b-positive) patients produced more IgG3 antibodies than f-negative patients.  The difference between geometric mean values of opposite homozygotes (f/f versus f-negative) was 2.3-fold (p = 0.0113).  This finding indicates that the b-positive gamma-3 allele is more productive than the g-positive allele.