A continuum of cells leading to an in-vivo humoral response.

A fortuitous series of observations reported in 1955-56 allowed the first demonstration that a lymphoid structure, the bursa of Fabricius, exerts a profound influence on humoral immunity. These and later studies contributed to our understanding of the role of the cell in immunology and, in particular, to the T- and B-cell concept. The bursa gained acceptance as an exporter of specialized lymphocytes following the demonstration of certain bursa-dependent cell populations in specific regions of peripheral lymphoid tissue such as thegerminal centre. Here Bruce Glick and Imre Olah discuss a newly identified family of cells which they believe may influence B-cell differentiation.