Low IgG subclass levels in brittle asthma and in patients with exacerbations of asthma associated with respiratory infection

Serum total immunoglobulin (G, A, M and E) and IgG subclass levels were studied in 23 patients with brittle asthma, 23 age-and sex-matched patients with mild asthma and 33 patients with recurrent infective exacerbations of their asthma. Patients with brittle asthma showed significantly reduced levels of IgG (mean +/- SD, 8.8 +/- 3.3 g l(-1)) compared to patients with mild asthma (11.0 +/- 2.5 g l(-1)) (P<0.008) with further significant reductions in the brittle compared to the mild group in IgG(1) (5.2 vs 6.3, P=0.035), IgG(2) (2.4 vs 3.25, P<0.006), IgG(3) (0.39 vs 0.55, P<0.05) and IgA (1.91 vs 2.38, P<0.03), There were no significant differences between the brittle group and the group with recurrent infective exacerbations for any parameter, but the latter group showed significantly reduced levels of IgG (8.2, P<0.001), IgG(1) (4.9, P<0.00001) and IgG(2) (2.5, P<0.02) compared to the mild group. In all groups. there was no relationship between dose of inhaled steroids and levels of any antibody. These findings suggest that the presence of a mild degree of humoral immunodeficiency relates to severity of asthma, and suggests that immunoglobulin replacement therapy may be appropriate in patients with the more severe forms of asthma.