Coexistence of (Partial) Immune Defects and Risk of Recurrent Respiratory Infections (Clinical Immunology‪)‬

Streptococcus pneumoniae and Haemophilus influenzae are important bacteria in recurrent respiratory infections (1). The immunological response against them is based on the synthesis of specific immunoglobulins, the generation of complement factors, and phagocytosis. Antibodies to polysaccharide antigens of S. pneumoniae and H. influenzae are important in protection against these microorganisms (2,3). The IgG2 subclass is the main antipolysaccharide antibody and patients with IgG2 subclass deficiency are more prone to develop pneumonia, sinusitis, and invasive pneumococcal disease (4). The G2m(n) allotype of IgG2 has been associated with increased susceptibility to infections with encapsulated bacteria (5). The link between IgG2 and phagocytosis of encapsulated bacteria is constituted by Fc[gamma] receptor (R) IIa, the only Fc[gamma] receptors that bind IgG2 (6). Fc[gamma]RIIa exhibits allelic polymorphism with different capacities for binding IgG2 and phagocytosis. A single nucleotide difference at base 494 (A or G) results in a histidine (H) or an arginine (R) at amino acid 131 of the protein. Fc[gamma]RIIa-H131 has a high affinity for IgG2, whereas Fc[gamma]RIIa-R131 has a low affinity for IgG2 (7).