Abstract
A diverse B cell repertoire is essential for an effective immune response. Not only to provide a variety of antibodies to recognise the Multiplicity of likely pathogen challenge, but also because B cells are important regulators of the immune response. In addition to their excellent capabilities as antigen presenting and activating cells, recent work shows that some subpopulations of B cells can have suppressive functions. The diversity of the B cell population as a whole decreases with age, and is associated with ill health. Whether decreased diversity is a feature of all B cells or a reflection of altered subpopulations is not clear, since different subsets of B cells have different functions and their repertoires are shaped by different selection pressures.