Presence of plasma cells binding autologous antibody during an immune response.

Spleen and other lymphoid tissues of rabbits immunized with human serum albumin (HSA) and human lactoferrin (LF) were examined for the presence of cells forming anti-idiotype antibodies. To detect these cells, IgG, F(ab')2, or Fab' of specific antibodies were isolated, fluorochrome-tagged with tetramethylrhodamine isothiocyanate, and used as an idiotypic marker to detect splenic plasma cells that are producing anti-idiotypic antibody. By this procedure, we were able to demonstrate anti-idiotypic cells in surprisingly high numbers. For example, in six rabbits immunized with HSA for periods ranging from 36 to 542 d, the percentage of Ig-positive cells that stained with autologous idiotype ranged from 0.7 to 44; furthermore, cross-reactivity was observed among seven different anti-HSA preparations and two anti-LF antisera. The isotype of anti-idiotypic cells, determined by costaining with fluorescein isothiocyanate-labeled goat Fc-specific anti-rabbit Ig, was shown to be predominantly IgG. These findings provide evidence of the presence of plasma cells producing antibody to autologous idiotype during a vigorous immune response.