Impaired pneumococcal antibody response in bronchiectasis of unknown aetiology.

As a defective anti-polysaccharide response can exist in the absence of an immunoglobulin deficiency, a series of 26 patients with bronchiectasis of unknown aetiology was vaccinated with a 23-valent pneumococcal polysaccharide vaccine. All patients suffered from recurrent respiratory tract infections. When measuring total antibody levels to pneumococcal serotypes 3, 4 and 9, a normal polysaccharide antibody response was found in 22 patients. However, only 11 of these subjects showed a normal pneumococcal antibody response within the IgA and/or IgG2 subclass, and thus could be classified as true responders, while 15 patients did not respond in either the IgA class or in the IgG2 subclass. When analysing differences between the responder (n = 11) and nonresponder (n = 15) groups, the latter demonstrated higher frequencies of respiratory tract infections and more severe lung pathology, as revealed by the presence of more bronchi visualised in the peripheral third of the lung by high-resolution computed tomography scanning. Moreover, nonresponders needed extensive lung surgery more often in order to control their disease (number of resected segments eight versus five). In conclusion, an important fraction of patients presenting with idiopathic bronchiectasis is associated with a selective anti-polysaccharide response deficiency and this subgroup appears to represent a more severe clinical phenotype. Therefore, it can be regarded as a separate clinical entity with possible therapeutic targets. In order to identify IgA and IgG2 anti-polysaccharide nonresponders, all patients presenting with bronchiectasis of unknown aetiology should be immunised with a pneumococcal polysaccharide vaccine, and IgA and IgG2 isotype responses should be evaluated as well as the total antibody response.