PROLIFERATIVE COMPARTMENTS IN THE NORMAL NAIL UNIT

The main distinction between the germinal matrix and the nail bed is t hat the former is the origin of all or most of the nail plate and the latter provides an epithelial surface to which the emerging nail can a dhere. It has been argued that the nail bed may contribute substance t o the nail plate and it is likely that if this was the case, epithelia l proliferation in the nail bed would match that in the germinal matri x by a proportion appropriate to its contribution, We have measured th e labelling index (LI) in the three major anatomical sites of the nail unit using two antibodies to antigens expressed in cycling cells, Usi ng Ki-67 (MIB-1) and proliferating cell nuclear antigen (PCNA) as mark ers of cell proliferation we have defined the LI in the germinal matri x (MIB-1: 22.1%, PCNA: 33%), nail bed (MIB-1: 0.75%, PCNA: 1%) and dig it pulp (MIB-1: 16.8%, PCNA: 17.4%), This suggests a low degree of pro liferation in normal nailed consistent with a minimal or non-existent contribution to the nail plate. This may change in hyperkeratotic nail dystrophies, where the nail bed LI is raised (MIB-1: 31%, PCNA: 29%), illustrating how nail bed behaviour can alter with disease.