Impaired Ige responses in a child with homozygous C2 deficiency and recurrent pneumococcal septicaemia

Homozygous deficiency of the second component of complement (C2) is the mos t common inherited deficiency of complement (1). Although C2 deficiency has been detected in asymptomatic individuals, patients usually present with e ither autoimmune disease or recurrent pyogenic infection, particularly due to encapsulated bacteria such as Streptococcus pneumoniae, Haemophilus infl uenzae type b and Neisseria meningitidis. Interestingly, infection is the m ost common mode of presentation of C2 deficiency in young children (1). An association between C2 deficiency and IgG subclass deficiency has also been previously described (2-4). We now report a female child with C2 deficienc y that presented at the age of 3 mo with recurrent pneumococcal septicaemia . Although IgG subclass levels were normal, specific IgG responses to vacci nation against S. pneumoniae and H. influenzae were significantly impaired.