A 4 yr old child has repeated pyogenic infections with organisms having polysaccharide capsules. Which of the following deficiencies need to be investigated?

IgG2 is directed against polysaccharide antigens and is an impoant host defense against encapsulated bacteria. Since this patient is suffering from recurrent infections caused by organisms having polysaccharide capsules he should be investigated for IgG2 deficiency. Each IgG molecule consists of two L chains and two H chains linked by disulfide bonds. There are four subclasses (IgG1 to IgG4), based on amino acid sequence differences in the H chains and on the number and location of disulfide bonds. IgG1 constitutes 65% of the total IgG.