Increase in density of jejunal IgA2 cells during infancy without change in IgA1 cells

To determine any association between densities of cells containing IgA, IgA1, IgA2, IgG, and IgM in the lamina propria of the jejunum and the age of the individual, we restudied 65 specimens from 65 patients in the age range 66 days to 4 years. Indications for jejunal biopsy were minor symptoms; none of the patients had any gastrointestinal disease, and the specimens showed normal morphology. We used murine anti-human monoclonal antibodies to IgA, IgA1, IgA2, IgG, and IgM and an indirect immunoperoxidase method and found a significant increase with advancing age in the densities of cells containing IgA, IgA2, and IgG, whereas the densities of IgA1- and IgM-positive cells did not change with age. Densities of IgA2 and IgG cells in children over 1 year were significantly greater than in infants under 9 months (upper vs. lower quartile of the study group, p < 0.05 in both comparisons). In the jejunum, an increase in IgA2 cells was responsible for the increase in total IgA production for the age range studied.