Development of immunoglobulin A in infancy and childhood.

Serum and salivary concentrations of immunoglobulin A1 (IgA1) and IgA2 were studied in 105 Icelandic children aged 0-12 years. Serum concentrations of both IgA1 and IgA2 increased slightly (P < 0.001) during childhood. The salivary IgA1/IgA2 ratio tended to decrease during the same period; this trend is less apparent when omitting the youngest children. The salivary IgA1 and IgA2 output could be high, even in children with low levels of serum IgA. Only polymeric IgA was found in whole saliva. Interestingly, in serum, most IgA1 and IgA2 were polymeric during infancy. The proportion of polymeric IgA decreased, when the concentration of IgA increased. The polymeric form of IgA might provide the infant with better protection against invading microorganisms by activation of the innate immune mechanisms.