CORRESPONDENCE accompanies immunizations12. But clonal cell division might permit somatic mutation, the raw material of affinity maturation, assuming that there is self-antigen present to perform the selection process of the activated anti-self clonal precursors. Finally, polyclonal activation with proliferation carries with it a potential benefit. Such a process should produce antibodies reflecting the entire immunological history of the host (and perhaps a modest sample of its future potential as well). As Ahmed and Oldstone pointed out 20 years ago2, the stimulation of bystander B cells by any polyclonal activator may be a significant contributor to the maintenance of long-term immunological memory in the absence of specific antigenic stimulation.