INTESTINAL B-CELL ISOTYPE RESPONSE IN RELATION TO LOCAL BACTERIAL LOAD - EVIDENCE FOR IMMUNOGLOBULIN-A SUBCLASS ADAPTATION

Background and Aims: In experimental animals, the indigenous microbiot a modulates mucosal immunity. In humans, such direct evidence is scarc e. The aim of this study was to examine the effect of intestinal bacte ria on the local immunoglobulin (Ig) response. Methods: The numbers of IgA-, IgM-, and lgG-producing immunocytes per defined mucosal length unit were determined, and the local IgA subclass response was studied using immunohistochemistry in jejunal segments from adults with bacter ial overgrowth and in sterile ileal urinary conduits from children. Re sults: The ileal bladder mucosa showed atrophy, but the number of immu nocytes only tended to be decreased. The jejunal segments with bacteri al overgrowth showed minor histological changes; the numbers of IgA an d IgG immunocytes were fairly normal, whereas the number of IgM immuno cytes was significantly reduced (P < 0.05) (12 cells/ U) compared with control mucosa (24 cells/U). The number of IgA2 immunocytes was signi ficantly decreased (P < 0.01) in ileal conduits (7 cells/U or 30% of t otal IgA) but increased (P < 0.05) in jejunal segments with bacterial overgrowth (42 cells/U or 43% of total IgA) compared with normal ileum (15 cells/U or 40% of total IgA) and jejunum (24 cells/U or 23% of to tal IgAf. Conclusions: An association exists between bacterial load an d IgA subclass production. An increase in IgA2 may enhance mucosal pro tection and probably reflects immunomodulation caused by lipopolysacch arides.