In 1965, Max Cooper and Robert Good published a landmark study in Nature that led to the birth of the B cell field. Working with chickens, they showed that cells that develop in the bursa of Fabricius ('B cells') are responsible for antibody production, whereas those cells that develop in the thymus ('T cells') are necessary for delayed-type hypersensitivity responses.

50 years on, we have a better understanding of the developmental pathways and diverse immune functions of B cells. Not only are these cells important for the generation of antibody-producing plasma cells and immunological memory, but they regulate diverse immune responses through their production of cytokines and other immune mediators.

The Review articles in this Focus issue discuss the mechanisms involved in B cell selection in the germinal centre and their subsequent development into memory B cells and plasma cells. The authors explain the importance of these processes for providing protective immunity to pathogens, but also highlight their contribution to diseases such as B cell lymphomas. In our Timeline articles, Max Cooper himself chronicles the early history of the B cell, while Shane Crotty takes a look back at the key events that helped to define the crucial role of CD4⁺ T cells as supporters of B cell-mediated immune responses.

The Nature Reviews Immunology team are delighted to present this Focus issue in celebration of the golden anniversary of the B cell. It's safe to say — B cells remain nifty at fifty!