Some studies have observed the direct effects of ritonavir (RTV) on immune cell activation, proliferation, and susceptibility to apoptosis, showing how RTV inhibits the activation and proliferation of primary endothelial cells and decreases the production of tumor necrosis factor alpha (TNF-alpha), IL-6, IL-8, and VEGF, which are all responsible for the development of KS lesions [85,86]. Here, IL6 is linked to Kaposi's sarcoma.