We characterized 121 adults with frequent or severe bacterial
respiratory tract infections at diagnosis of selective subnormal
IgG3. Mean age was 47 ± 13 (SD)y; 87.6% were women. Associated disorders included: autoimmune conditions 33.1%;
hypothyroidism 14.9%; atopy 29.8%; and other
allergy manifestations 41.3%. In 34.1%, proportions of protective Streptococcus pneumoniae serotype-specific
IgG levels did not increase after polyvalent pneumococcal
polysaccharide vaccination. Blood CD19+, CD3+/CD4+, CD3+/CD8+, and CD56+/CD16+ lymphocyte levels were within reference limits in most patients. In regression analyses, independent variables age; sex; autoimmune conditions;
hypothyroidism; atopy;
allergy manifestations;
corticosteroid therapy; and lymphocyte subsets were not significantly associated with
IgG subclass,
IgA, or
IgM levels. Frequencies of HLA haplotypes A*01, B*08; A*02, B*14; A*02, B*15; A*02, B*44; A*02, B*57; and A*03, B*07 were greater in 80 patients than 751 controls. We conclude that subnormal
IgG3 and non-protective S. pneumoniae
IgG levels contribute to increased susceptibility to
respiratory tract infections.