B-cell development in lamina propria of the large intestine: influence of age and t-cell densities.

The development of B-cells and immunoglobulin-isotype and IgA subclass-positive cells in the lamina propria of the large intestine during infancy was investigated. Biopsy specimens from 36 infants, taken for diagnostic purposes, were available. All samples showed normal morphology. Monoclonal antibodies to CD22, IgA, IgA1, IgA2, IgM and IgG and a peroxidase method were used to demonstrate positive cells in the cryostat sections. Cell densities were counted from a known area. T-cells had been measured in a previous study using the same specimens. The density of CD22+ cells was already high in infants below the age of 1 month and increased little with age. Four specimens from infants below the age of 40 days lacked IgA-, IgA1- and IgA2-positive cells. The densities of these cells increased with age; the correlation coefficient between the age and the density of the cells was for IgA: R=0.47, p=0.04; for IgA1: R=0.57, p=0.001, and for IgA2: R=0.34, p=0.04. The densities of IgG- and IgM-positive cells remained unchanged with age. The negative correlation between density of IgG+cells and CD8+ cells in the lamina propria (R= -0.43, p=0.01) was significant. Strong local stimulation results in early accumulation of CD22+, IgM+ and IgG+ cells in the large intestine, but little change takes place after the first few days of life. The terminal differentiation to IgA-positive cells is slowest, and this population showed significant developmental change.