PARAFOLLICULAR BULGES, BUT NOT HAIR BULB KERATINOCYTES, ARE ATTACKED IN GRAFT-VERSUS-HOST DISEASE OF HUMAN SKIN

Graft-versus-host disease (GVHD) has been shown to preferentially atta ck epithelial stem cell regions in the rete ridge of epidermis, the pa rafollicular bulge stem cells of the hair follicle, the limbus of the eye, the basal cells of filiform papilla of the tongue and the stem ce ll regions of gut crypts. The parafollicular bulge, but not the papill ary bulb tip, has recently been shown to be the site of follicular ste m cells. The hair bulb at the tip of the papilla contains progeny of t he parafollicular bulge stem cells. These progeny in turn are a prolif erative population which gives rise to the hair. We asked the question : Does GVHD preferentially attack the younger, less differentiated pop ulation of cells in the parafollicular bulge but spare the also cyclin g, later generation of cells in the papillary bulb? We had 22 evaluabl e cases from our prior study of 38 biopsies of GVHD patients: 19 showe d preferential bulge involvement, 2 showed both involved, 1 showed nei ther involved and none showed bulb positive and bulge negative. The da ta support a strong preference for GVHD to attack the less differentia ted of two cell populations both of which are cycling, thereby support ing the hypothesis that preferred targets are related to the stem cell populations in epithelial and not just all cycling or proliferating p opulations.