IgA-Secreting Cells in the Blood of Premature and Term Infants: Normal Development and Effect of Intrauterine Infections

Abstract

It is now well appreciated that human infants at birth usually have undetectable levels of IgA in the serum, which slowly rise over the first few years of life to attain adult levels by puberty^1,2. Most newborns also lack secretory IgA (S-IgA) at birth, with IgA in the saliva or tears not detectable until the first wk. Increasing S-IgA levels are noted in the first few mo of life, sometimes being demonstrated before serum IgA (3,4, Cripps et al., this volumn). As noted by Moro et al., (this volume), as well as by others^5,6, the genetic and cellular mechanisms for the production of IgA responses are in place before birth, although induction of IgA responses would necessitate antigenic stimulation in utero. However, the subset of B cells involved in the production of serum or S-IgA is still unclear. The B cells found in several fetal organs and in the blood of the fetus and neonate are primarily of the CD5⁺ rather than the CD5^- subset; the latter represent the majority of B lymphocytes in human adults^7–9.