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 IgG1 (5.2 vs 6.3, P = 0.035), IgG2 (2.4 vs 3.25, P < 0.006), IgG3 (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), IgG1 (4.9, P < 0.00001) and IgG2 (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.