In a 5-year-old boy who has history of recurrent pyogenic infections by bacteria with polysaccharide-rich capsules, which of the following investigations should be done?

Ans. (d) IgA and IgG, deficiency Ref. Harrison 18/e, p 2704, 19/e p 2108 "IgG subclass deficiency may be suspected in children and adults who have a history of recurrent infections of the ears, sinuses, bronchi and/or lungs." Antibodies against the polysaccharide, coating (capsule) of ceain disease-producing bacteria (e.g. the pneumococcus and Haemophilus influenzae) are predominantly of the IgG2 type. These patients are unable to produce protective levels of antibody when immunized with unconjugated polysaccharide vaccines against Streptococcus pneumonaiae (the pneumococcus) or Haemophilus influenzae bacteria and are prone for infections by capsulated bacteria. Ig G2 deficiency is frequently associated with deficiency of IgA. Note- Overall IgA deficiency is the most common primary immunodeficiency.