Polyclonal B-cell activation by bacteria that induce nonsuppurative sequelae

The polyclonal B cell activation (PBA) process induced by Klebsiella pneumoniae K34 (klebs) and Yersinia enterocolitica 03 (yers) was investigated. Both heat-inactivated bacteria and their cell wall biostructures (klebsM, muriene, protein I etc.) stimulate human blood B cells to differentiate into immunoglobulin-secreting cells without prior proliferation and without T cells. Klebs-activated B cells secrete mainly IgM and to a lesser degree IgG (mainly IgG₂). The PBA process was regulated by CD4⁺ cells and monocytes, but not by CD8⁺ cells. While interleukin 2 is able both to induce proliferation and to enhance differentiation in klebs-activated B cell cultures, the low-molecular-weight B cell growth factor (BCGF) did not lead to a significant amount of ³H-thymidine uptake. In addition, in klebs-activated B cell cultures various anti-polynucleotide autoantibodies and the 16/6 idiotype were detectable. Thus, bacteria that induce nonsuppurative sequelae (e.g. klebs, yers) can use several mechanisms to overcome tolerance in their host.