Terminally differentiated human intestinal B cells. J chain expression of IgA and IgG subclass-producing immunocytes in the distal ileum compared with mesenteric and peripheral lymph nodes

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Abstract
Two‐colour immunofluorescencc staining for intracellular J chain and IgA (or J chain and IgG) was performed on tissue sections of normal human ileal mucosa (eight adult kidney donors), mesenteric lymph nodes (MLN), peripheral lymph nodes, and palatine tonsils. The most prominent J chain positivily was seen for IgA (97.3%) and IgG (81.7%) immunocytes in the ileal lamina propria (LP). Moreover, the proportion of J chain‐expressing exlrafollicular immunocytes was significantly higher (P < 0.05) in MLN than in peripheral lymph nodes for the IgA class (58.5%versus 25.6%); the same proportion for the IgG class was 45.9%versus 30.4%. In clinically normal palatine tonsils of adults, extrafollicular J chain expression was much lower than in peripheral lymph nodes; 14.2% for IgA cells and 5.5% for IgG cells. When related to subclass production, J chain expression was found to be higher for IgA2 than for IgA 1 cells in all tissues examined (palatine tonsils excluded because of a small number of lgA2 cells), the difference being significant in M LN and ileal LP (P < 005). The J chain positivity tended to be higher for all IgG subclasses in MLN than in peripheral lymph nodes; this difference was significant (P <005) for lgG2‐producing immunocytes. Taking J chain expression as a marker of clonal immaturity, our results may reflect to some extent distribution of newly generated memory B cell clones from gut‐associated lymphoid tissue to MLN. peripheral lymph nodes, and palatine tonsils in a strikingly decreasing order.