Immune privilege (IP) is believed to exist in the anagen hair follicle (HF). 
Studies have shown that downregulation of major histocompatibility complex Class 
I occurs and immunosuppressive factors are expressed in the HF bulb and bulge. 
However, demonstration and quantification of functional IP in HF cells are 
required. We examined the middle (sheath) and lower (bulb) portions of the human 
HF using quantitative real-time RT-PCR (qPCR), immunohistology, ELISA, in vitro 
coculture with peripheral blood mononuclear cells (PBMCs), and flow cytometry. 
We found that HF cells, relative to non-follicular epidermal cells, failed to 
promote allogeneic PBMC proliferation and CD4(+) and CD8(+) IFNγ production. By 
qPCR, we found significant downregulation of Class I and Class II HLA alleles in 
both the bulb and sheath, and upregulation of multiple immunoregulatory genes. 
It is noteworthy that somatostatin (SST) was significantly upregulated relative 
to epidermis. By immunohistochemistry, SST was most strongly expressed in the HF 
outer root sheath, and, by ELISA, cultured sheath cells secreted SST. PBMCs, 
cultured with stimulatory allogeneic epidermal cells and SST, secreted 
significantly less IFNγ than controls. Addition of SST antagonists to PBMCs 
cocultured with allogeneic HF cells increased IFNγ secretion. The data identify 
SST as a secretory factor potentially contributing to the HF IP repertoire.