|dc.description.abstract||Bronchiectasis is a common chronic debilitating respiratory condition with
patients suffering chronic cough, sputum production and recurrent chest
infections. Specific immune defects can be associated with bronchiectasis in
up to 10% of patients.
There are four Immunoglobulin G subclasses (IgG1, IgG2, IgG3 and IgG4).
IgG2 primarily binds carbohydrates found in the bacterial outer membrane
and capsules, which makes IgG2 an important part of the pulmonary defence
against gram positive and negative bacteria. IgG2 deficiency is the most
frequently identified in patients with bronchiectasis but its clinical significance
is not known.
We assessed bronchiectasis patients in the bronchiectasis clinic that had
IgG2 deficiency and matched patients that were IgG2 replete. Furthermore
serum neutrophil phagocytosis assays of PAO1 were performed and
compared between the groups.
Information of 27 IgG2 deficient patients and 27 patients with normal IgG2
levels were matched for statistical analysis and comparison, which showed
that 67% of deficient patients and 56% of control patients are chronically
infected with pathogenic organisms. The most common bacterial pathogens
isolated were: Haemophilus influenzae, Pseudomonas aeruginosa,
Coliforms, Staphylococcus aureus, Streptococcus pneumoniae and
Moraxella catarrhalis. There was no significant difference in age, body mass
index, smoking status, lung function, CT score and sputum purulence
between the deficient and the non-deficient patient group. In deficient
patients, there were significantly lower IgG2 levels and the IgG2 percentage
of the total IgG, with an increased Bronchiectasis Severity Index score, an
increased frequency of chronic infection with Pseudomonas aeruginosa and
Coliforms and an increased number of exacerbations. The phagocytosis
assays showed no significant difference between the two groups.
In conclusion, IgG2 deficient patients had a more severe phenotype with
increased chronic infection with Pseudomonas species and increased
exacerbations. Preliminary investigations show the same peripheral
neutrophil phagocytic capacity for PAO1 but further work is needed to
explore this further.||en