Plastic‐immobilized anti‐μ or anti‐δ antibodies induce apoptosis in mature murine B lymphocytes

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Abstract
It is widely accepted that extensive cross‐linking of surface immunoglobulin (sIg) receptors on mature B cells promotes their activation and progression through the cell cycle. A commonly employed method to maximize receptor cross‐linking via anti‐receptor antibodies is to immobilize them on tissue culture plastic. We show here that immobilizing monoclonal anti‐μ or anti‐δ antibodies, which are mitogenic in solution, on plastic abrogates their capacity to induce DNA synthesis in mature murine B cells, even in the presence of interleukin‐4 (IL‐4). The cells do become abortively activated, as evidenced by up‐regulation of major histocompatibility complex class II antigen levels, but subsequently virtually all of them die, manifesting DNA fragmentation characteristic of apoptosis. The induction of apoptosis is abrogated by the inclusion of either IL‐4 or anti‐CD40 antibodies in the cultures, with the two stimuli acting in concert. We believe that the system represents a polyclonal model of clonal deletion tolerance in mature B cells, such as may be induced under physiological conditions by antigens with repeating epitopes.