Activated pneumococcal polysaccharide (PPS)-specific human B lymphocytes have been purified and examined in vitro. They are large cells that are refractory to further activation by antigen, anti-Ig, or Staphylococcus aureus Cowan strain I, but they respond directly by proliferation to B cell growth factors. In addition, they express the isotype pattern of activated cells and a surface marker of activated lymphocytes called 4F2. Finally, they contain a subset of cells that spontaneously secrete PPS-specific antibody.

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