As a result, in spite of the relatively robust viral replication resulting in levels of viremia, which are similar or higher than those observed during pathogenic SIV infection, the natural hosts of SIVs do not display any of the hallmarks of HIV disease progression, i.e., breakdown of the gut epithelial barrier, microbial translocation, and chronic T-cell immune activation and inflammation, CD4+ T-cell decline, or hypercoagulation (6, 28, 52, 122, 130, 151–153). Here, CD4 is linked to thrombophilia.