| Abstract: | Previous experimental work demonstrated that clonal variation occurs in vitro. The present experiments were designed to test for clonal variation in vivo. B cells were transferred at limiting dilution, with antigen, into irradiated recipients. Seven days later spleens were assayed for plaque-forming cell (PFC) colonies. Control experiments showed that these PFC colonies were clones, that is, they were derived from a single B cell precursor. When the clones were analyzed for heterogeneity of the PFC population, using cross-reactivity on various mixtures of red blood cells as a method of detecting differences in antibody specificity, form 23–83 % of the clones contained variants. By adjusting the amounts of helper activity and antigen available to a developing clone, we have been able to influence this variation; high levels of help and/or antigen favour pure clones, while low levels of either produce mainly mixed clones. |
