Alpha-defensins, theta-defensins and their synthetic analogues the retrocyclins have been shown in numerous studies to have anti-HIV-1 activity (Chang & Klotman 2004). This appears to be mediated via multiple mechanisms including direct viral inactivation and down regulation of host-cell target co-receptors important for viral entry (Furci et al. 2007, Seidel et al. 2010). HNP1-3 act as lectins, binding with relatively high affinity to gp120 (KD range, 15.8-52.8 nM) on the HIV-1 envelope and CD4 (KD range, 8.0-34.9 nM) on host target cells, both important molecules for viral entry (Wang et al. 2004). Retrocyclins, artificial theta defensins predicted from human defensin pseudogenes, bind with even higher affinity whereas HNP-4 binding is much weaker (Wu et al. 2005). Alpha defensins have been demonstrated to inhibit the binding of gp120 to CD4 thus blocking HIV-1 fusion with its target cells (Furci et al. 2007).