The pathogenesis of alopecia areata.  Antigen-presenting cells, such as Langerhans cells, are increased in the bulb of the affected follicles.  They present the responsible epitope to the peribulbar lymphocytes.  This leads to a cascade of immunologic events with increased interleukin-2 (IL-2), gamma interferon (gamma IFN) and intercellular adhesion molecules (ICAM).  This series of events helps to induce hair loss.  This is considered to be a Type I helper T-cell response (Th1).