Normal human intestinal B lymphocytes. Increased activation compared with peripheral

The state of activation of normal human intestinal mononu-clear cells obtained from transplant donors was studied. Com-pared with PBMC, freshly isclated intestinal mononuclear cells expressed significantly more cell surface activation anti-gens on both B and T lymphocytes. Intestinal mononuclear cells contained significant numbers of immunoglobulin secret-ing cells immediately after cell separation. This population included CD5-positive B cells that secreted predominantly IgA. Cells from the large bowel consistently revealed higher numbers of IgA secreting cells than cells from the small bowel. Thus, intestinal B cells are markedly activated in vivo com-pared with PBMC and this increased activation correlates with increased spontaneous antibody secretion. B cells from the large intestine are more highly activated and secrete more an-tibody than do cells from the small intestine. The intestinal lamina propria lymphoid compartment exhibits a heightened state of activation that may be important for its distinct role in mucosal defense