Human tonsil, blood and bone marrow in vivo‐induced B cells capable of spontaneous and high‐rate immunoglobulin secretion in vitro: Differences in the requirements for factors and for adherent and bone marrow stromal cells, as well as distinctive adhesion molecule expression

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Abstract
Human B cells capable of spontaneous IgG secretion are commonly found in circulation and in lymphoid tissues such as tonsil and bone marrow (BM). The present study compares the mechanisms that regulate tonsil, blood and BM B cells capable of spontaneous IgG secretion. The BM cell subset produced IgG during a markedly longer period of time (14 days) than did tonsil and blood cell subsets (2–3 days). Blood and BM, but not tonsil, B cell IgG secretion depended on the presence of adherent cells, as demonstrated by adherent cell depletion and re-addition experiments. Stromal BM cells supported linear IgG secretion by non-adherent BM cells for 2 weeks, but were unable to prolong the short-term IgG secretion by tonsil and blood cells. Different factors induced IgG secretion in each of the three B cell populations as optimal IgG secretion by tonsil, blood or BM cell subsets required either tumor necrosis factor-α, interleukin-6 or fibronectin + interleukin-6, respectively. Finally, these populations also showed differences in the expression of adhesion molecules; the tonsilar cell subset was PNA+/− CD44+ CD49d+ CD49e− Leu-8+/−, the blood cell subset was PNA− CD44+/− CD49d+ CD49e− Leu-8+ and the BM cell subset was PNA− CD44+/− CD49d+ CD49e− Leu-8−. These results suggest that the mechanisms controlling the final differentiation and the expression of adhesion molecules in these B lymphocytes exhibit territorial specificity.