Notably, the presence of HLA Cw*0602, a risk allele of psoriasis, was present in 79% of HIV-positive patients with psoriasis, compared with 24.5% of HIV-infected patients without psoriasis (64), suggesting that lymphopenia due to HIV infection likely triggers expansion and differentiation of skin-reactive T cells with higher affinity to a particular MHC risk allele. This evidence concerns the gene HLA-C and psoriasis.