Significance of HLA antigens and the mixed lymphocyte reaction in psoriasis

Human Major Histocompatibility (HLA) complex antigens B13, BW16, BW17, CW6 and D-MA are increased in frequency in patients with psoriasis. Of these, the strongest association is with HLA-CW6 and D-MA, with a relative risk of 10.4. Since no strong association with any HLA-A locus antigen is seen, it seems likely that the disease susceptibility gene for psoriasis lies close to the HLA-D locus, which is defined by the use of the mixed lymphocyte reaction (MLR). In the mouse, the Immune response (Ir) genes are found in the MLR region and it is thought that Ia antigens lie at a corresponding location in man. Recently, we have demonstrated that human epidermal cells cause stimulation in the mixed lymphocyte reaction. Lymphocyte antigens which stimulate in this reaction are known to be products of HLA genes and anti-HLA-D sera block stimulation by epidermal cells. It is possible that these antigens may be involved in the regulation of cell--cell communication. Psoriasis is a disease characterized by epidermal hyperproliferation. It is possible, therefore, that an HLA-linked deficiency of recognition between epidermal cells exists in patients with psoriasis and that this defect allows abnormal cellular proliferation to occur.