The rate of psoriasis in human immunodeficiency virus-positive (HIV) individuals is comparable to that of HIV-negative individuals, but psoriasis tends to be more severe in people infected with HIV. A much higher rate of psoriatic arthritis occurs in HIV-positive individuals with psoriasis than in those without the infection. The immune response in those infected with HIV is typically characterized by cellular signals from Th2 subset of CD4+ helper T cells, whereas the immune response in psoriasis vulgaris is characterized by a pattern of cellular signals typical of Th1 subset of CD4+ helper T cells and Th17 helper T cells. The diminished CD4+-T cell presence is thought to cause an overactivation of CD8+-T cells, which are responsible for the exacerbation of psoriasis in HIV-positive people. Psoriasis in those with HIV/AIDS is often severe and may be untreatable with conventional therapy. In those with long-term, well-controlled psoriasis, new HIV infection can trigger a severe flare-up of psoriasis and/or psoriatic arthritis.
