To obtain a clearer understanding of whether SerpinB2 is induced during lentivirus infections in vivo, we analyzed SerpinB2 mRNA and protein expression in serial PBMC samples obtained from pigtail macaques infected with 2 primate lentiviruses; (i) SIVmac251, which utilizes the CCR5 co-receptor to enter cells and therefore readily infects macrophages as well as memory CD4 T cells [21], or (ii) the highly pathogenic SHIVmn229, which utilizes the CXCR4 co-receptor to enter cells and therefore primarily infects naïve CD4 T cells [22]. This evidence concerns the gene CD4 and lentivirus infection.