Polyclonal activation of the murine immune system by an antibody to IgD V. Effect on germinal centers.

Heterologous anti-mouse delta chain has been shown to induce T-independent polyclonal B cell proliferation by 24 h after injection into mice and a T-dependent polyclonal increase in the number of IgG-secreting cells in spleen and lymph nodes 6 days after injection. The effect of anti-delta on germinal center cells has been difficult to determine, however, since anti-delta-induced blast transformation of mantle zone cells makes it difficult to distinguish these cells from germinal center cells. To clarify the effect of anti-delta on germinal centers, we stained lymph node sections from control and anti-delta-injected mice with peanut agglutinin conjugated to horseradish peroxidase which clearly differentiates the germinal center cells from other large and small lymphoid cells. For the first 5 days after i.v. injection of goat anti-mouse delta, the germinal center volumes did not differ significantly from those of mice injected with control antibodies. On days 6 and 7 after injection, the lymph node germinal center volumes of anti-delta-treated mice increased on average over 10-fold as compared to those of mice injected with an equal amount of control antibody. Thus, while anti-delta antibody directly induced blastogenesis of mantle layer B cells, it appears to have little direct effect on germinal center cells. In contrast, rapid germinal center development is seen in anti-delta-injected mice during the T-dependent phase of B cell activation and occurs simultaneously with the appearance of large numbers of IgG-secreting cells.