IgG subclasses in foetal cord and maternal serum: associations with infections in infancy and smoking in pregnancy.

We have investigated the associations between levels of umbilical cord and maternal IgG subclasses with maternal smoking habits in pregnancy and infection rate during the first year of life following the birth of 93 normal infants. There was a wide degree of normal biological variation of subclass levels between infants and also within mother/infant pairs. There were higher serum levels of IgG-1 in smoking mothers (P less than 0.001) compared to non-smokers. One year follow-up of the infants' infection rate was evaluated by postal questionnaire (n = 72; 77% response rate). There was a weak but significant inverse correlation between foetal cord levels of IgG-2 and infection rate (r = -0.38). There was however no observable increase in infection in the infants of smoking mothers despite reduced birth weight, increased IgG-1 levels and the continued exposure to passive smoking during the first year. The possible mechanisms of a longterm protective effect against infection of maternally derived IgG-2 and the effects of maternal smoking are discussed.