Toward defining a 'lineage'--The case for dendritic cells

The immune system consists of a heterogeneous ensemble of cell types that immunologists have tried to classify and order for decades. This classification has relied on varying criteria, resulting in major debates in the immunology community. Discovered in the late 1970s [1], dendritic cells (DCs) are no exception, and their membership to a distinct immune lineage is still vividly debated [2-6]. Here, we review recent work on the origin of DCs and discuss the possible definition of a separate 'DC lineage'.