Pneumococcal antibodies and complement during and after periods of recurrent otitis

Combined IgG2, IgG4 and IgA deficiency: low C1q concentrations and the presence of excess C1r and C1s in an adult patient with recurrent pneumococcal infections

The complement (C) profile was investigated in an adult patient with combined IgG2, IgG4 and IgA deficiency and recurrent pneumococcal infections. The analysis revealed no gross impairment of the classic and alternative pathways of C activation. However, the concentrations of circulating C1q were persistently decreased, and the sera contained an excess of C1r-C1s complexes, resembling the C1 aberrations previously found in children with recurrent acute otitis media. The concentrations of C4 in the patient were persistently low. This could be ascribed to partial C4 deficiency with lack of C4A variants. The patient's IgG and IgM antibody responses to pneumococcal capsular polysaccharides and to other bacterial carbohydrate antigens were very poor. Interestingly, pneumococcal C-polysaccharide (CPS) could be detected in serum obtained during infection-free periods. Since CPS has been shown to bind C1q without causing C1 activation, the possibility was considered that the C1 aberrations in serum were due to circulating CPS. After administration of intramuscular gammaglobulin to the patient, the serum C1q levels were observed to return to normal.

Recurrent otitis media: genetic immunoglobulin markers in children and their parents

The likelihood that hereditary factors play a significant role in the development of recurrent acute otitis media (rAOM) in children has been suggested. The genetically determined immunoglobulin variants, Gm and Km, are useful tools for mapping out the genetic loci involved in antibody responses. Certain Gm and Km types, G2m(23) and Km(1), appear to be linked to genes which regulate the concentrations of antibodies to pneumococcal polysaccharide antigens in adults. Our aim was to identify such immunoglobulin markers in rAOM children, since these children have extremely low concentrations of IgG antibodies against the pneumococcal types associated with this disease. The markers G1m(1), G1m(2), G1m(3), G2m(23) and Km(1) were identified in 20 families, each comprising 1 parent and 1 child with a history of rAOM and 1 parent free from rAOM. In addition, G2m(23) was identified in 47 children without AOM. The distribution of Gm and Km markers between rAOM and healthy subjects did not differ significantly. If anything, rAOM children exhibited a high rate of the G2m(23) marker, whereas earlier observations in adults have demonstrated low responders to polysaccharide antigens to be preferentially G2m(-23). Our findings indicate that mechanisms responsible for the low concentrations of antibodies to pneumococcal polysaccharides in rAOM children may differ from those causing certain adults to be low responders when exposed to pneumococcal polysaccharides.

Antibody activity of IgG subclasses against pneumococcal polysaccharides after vaccination

The isotypic pattern of antipneumococcal polysaccharide antibodies with respect to IgG subclasses differs in adults and children. Adults show almost exclusively IgG2 activity, whereas children exhibit both IgG1 and IgG2 activity. The IgG subclass pattern of the antibody response after pneumococcal vaccination was evaluated in nine healthy children 1 to 2 years of age, eight healthy children 5 to 6 years old, and eight healthy adults. The number of individuals responding increased with age, and the response was mainly of the IgG1 subclass. The implications of this finding are discussed.

Defective immunocompetence in otitis-prone young children

In a prospective study highly otitis-prone children were found to have significantly lower levels of IgG 2 at 12 and 32 months of age compared to healthy age matched controls. As a confirmation of these results the same otitis prone children had significantly lower activity compared to healthy children with regard to specific antipneumococcal antibody activity of both the IgG 1 and IgG 2 subclasses. These findings support the concept that otitis proneness is partly due to a defective immunocompetence.