Delineation of producing ability of IgG and IgA subclasses by naive B cells in newborn infants and adult individuals

Abstract

SUMMARYNeonatal B cells with the naive (slgD"^) phenotype are able to generate IgG-and IgA-producing cells as well as IgM production in the presence of memory CD4'*' T cells expressing L-selectin (CD62L) in pokeweed mitogen-stimulated cultures. We used this system to examine comparatively the ability of naive B cells to produce IgG and IgA subclasses in newborn infants and adult individuals. Naive B cells were enriched from both donors on the basis of sIgD positivity, and memory (CD45RO'^) CD4"^ T cells with CD62L expression were isolated from adults. We here demonstrate some differences in profiles of IgG and IgA subclass production between neonatal and adult naive B cells. In neonatal B cells, IgGl and IgG3 were predominantly produced, but IgG2 and IgG4 production was virtually absent. Similar to neonatal B cells, adult naive B cells produced mainly IgGl and IgG3, although memory (sIgD") B cells from adults secreted all of the IgG subclasses. It should be noted that low but detectable levels of IgG2 and IgG4 were found in adults' naive B cell cultures. Although IgA produced by neonatal B cells was exclusively IgAl, IgA2-secreting cells were identifiable in adult naive B cells. The results suggest that further class switch of naive B cells to IgG2, IgG4 and IgA2 in addition to IgGl and IgG3 may be controlled by their own age-dependent maturation process.

Measurement of allergen-specific secretory IgA in stool of neonates, infants and toddlers by protection against degradation of immunoglobulins and allergens

“…The inhibitor spectrum indicates that protease(s) present in stool that degrade IgA, SIgA and allergens may be exogenous proteases, such as IgA1, IgA2, SIgA or IgG proteases in Escherichia coli (17,18) and other microbiota, rather than being leupeptin-and chymostatin-sentitive pancreatic proteases, trypsin and chymotrypsin, respectively. In this regard, reduced IgA immunofluorescence signals were not detected in the stool of 3day-old neonates probably because of immaturity (30). On the other hand, allergen -specific SIgA detected in the stool of 1 -monthold infants most likely originated from breast-fed milk from the mother, which immunoreacted with milk and egg allergens.…”

“…6). However, the stool extract of 3-day-old neonate did not show such immunofluorescence signals probably due to the lack of SIgA at that age (30).…”