Immunoglobulin A cell distribution in the human small intestine: phenotypic and functional characteristics

We compared B-cell phenotypes in Peyer's patches and solitary lymphoid foll icles (organized gut-associated lymphoid tissue, GALT) with those in jejuna l or ileal lamina propria. In situ, immunostaining showed that small B cell s of naive [surface immunoglobulin D-positive (sIgD(+)) CD27(-)] and memory (sIgD(+/-) CD27(+)) phenotypes occurred almost exclusively in GALT, wherea s the lamina propria contained only scattered sIgA(+) CD27(+) memory cells. In contrast, B-cell blasts and plasma cells negative for CD20 and often al so for CD19 but with strong expression of CD38, CD27 and cytoplasmic IgA (c IgA), dominated in the lamina propria but were scarce in GALT. By flow cyto metry, the proportion of dispersed CD19(+) B lymphocytes varied from 4 to 4 2% among jejunal mucosal samples; between 5 and 50% of these were sIgD(+), suggesting a variable contamination with GALT cells. B-cell blasts and plas ma cells, identified by their large size and strong expression of CD38, wer e regularly found (25-35% of the total mononuclear cell population). Distin ction between B-cell blasts and mature plasma cells was made by the presenc e or absence of human leucocyte antigen (HLA) class II molecules, CD45RA, C D19 and surface immunoglobulin. No CD19(+) B cells outside GALT expressed C D5, but a very small portion of the lamina propria B-cell blasts were posit ive for CD28. Dispersed sIgA(+) lamina propria cells expressed low levels o f CD40, proliferated on CD40 ligation and constitutively secreted IgA in vi tro. We concluded that the lamina propria B-cell compartment consists mainl y of B-cell blasts and plasma cells but also has scattered, small sIgA(+) c ells that can proliferate in response to CD40 ligation and may therefore fu nction as local memory cells for recall antigens.