Interleukin 2 and low molecular weight B cell growth factor are T cell‐replacing factors for different subpopulations of human B cells*

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Abstract
Both recombinant human interleukin 2 (rhIL2) and low molecular weight B cell growth factor (BCGFlow) were shown to be T cell‐replacing factors (TRF) in specific antibody responses to influenza virus by human blood and tonsillar B cells. When B cells were separated into high and low‐density populations on Percoll gradients at 1.074 kg/l, IL2 was found to act as a TRF only on the low‐density B cells, whereas BCGFlow was a TRF for high‐density B cells with a lesser effect on low‐density B cells. Both populations of B cells responded well in the presence of T cells. The high‐density B cells could not be activated to respond to IL2 by either IL1, rhIL4 or by a CD22 monoclonal antibody known to enhance B cell activation. In contrast, a 24‐h preincubation with T cells and antigen appeared to prime high‐density B cells to respond to IL2. These results show that high‐density B cells can in fact respond to TRF, and that IL2 and BCGFlow, act on different populations of B cells which may be defined by prior exposure to T cells.