Anti-pneumococcal polysaccharide antibody (anti-PPS) levels were measured in 153 serum samples collected from children aged between 2 and 47 months living in the highlands of Papua New Guinea (PNG). Fifty-seven of the samples were collected during acute episodes of lower respiratory tract infection (ALRI). Total IgA and IgG increased steadily with age; however, no association was found between the levels of these antibodies and the health status of the child. Total IgM levels showed little relationship to the age of the child but under 12 months of age levels were somewhat higher on average in children with pneumonia. For most of eight pneumococcal serotypes tested, specific IgG levels were found to decline rapidly in the first 6-8 months, reaching a minimum at approximately 12 months of age. Serotype 3 was exceptional in having very low titres in the youngest children. A separate analysis of 24 cord sera suggested that antibodies to this serotype do not usually cross the placenta in PNG. Children with pneumonia tended to have lower levels of specific IgG than healthy controls of the same age. Specific anti-PPS IgA levels were found to increase steadily with age, but were not associated with health statu
