Research: THINK POSITIVE

Professor Adrian Hayday and colleagues at King's College London have found that development of different kinds of T cell in the thymus is more closely linked than previously thought. The findings shed new light on key aspects of immune cell development.

The thymus, a gland found overlying the heart, is where the immune system's T cells develop. Two main types of T cell exist, αβ and γδ; broadly speaking, αβ cells circulate in the bloodstream tackling a diverse range of microbes, while γδ cells patrol the body's boundaries with the outside world, such as the skin and gut.

One of the most striking features of the thymus is the large number of T cells it generates, most of which are eliminated. Immature T cells – known as DP or 'double-positive' cells as they produce two key T-cell surface molecules – proliferate, but only those deemed to be of potential value in the fight against infection go on to later developmental stages.

In their latest research, Professor Hayday and colleagues discovered that this multitude of DP cells are not simply passively waiting to be chosen or culled: they also have a specific role of their own. The DP cells release factors (such as lymphotoxin) that act on neighbouring immature T cells, pushing them towards a γδ T-cell fate.

Thus, as well as generating the αβ T cells, these DP precursors also ensure that γδ T cells are produced – so the body has a balance between these two types of defence cell.

External links

• Silva-Santos B et al. Lymphotoxin-mediated regulation of gammadelta cell differentiation by alphabeta T cell progenitors. Science 2005;307(5711):925–8.