The clonal selection theory first proposed by Macfarlane Burnet is a cornerstone of
immunology. At the time, it revolutionized the thinking of immunologists because it provided
a simple explanation for lymphocyte specificity, immunological memory, and elimination of
self-reactive clones. The experimental demonstration by Nossal & Lederberg that B
lymphocytes bear receptors for a single antigen raised the central question of where B
lymphocytes encounter antigen. This question has remained mostly unanswered until …