Figure 7

Siglec-7 and susceptibility to HIV-1 infection. A, Chronic and high levels of HIV-1 replication in AIDS patients lead to the decreased surface expression of Siglec-7 on NK cells [31] and to higher levels of soluble Siglec-7 detected in the plasma of HIV-1 infected patients with elevated viral burden (Figures 5 and 6). HIV-1 is able to bind Siglec-7 (Figure 1) that, in its soluble form facilitates the infection of Siglec-7^neg/CD4^pos T cells (Figures 3 and 4). B, In contrast, high levels of viral replication do not affect the constitutive expression on monocytes and macrophage of Siglec-7 [14–31], which in turns, significantly contribute to HIV-1 infection of these cells. These experimental evidence suggest that, similar to other members of Siglec family [28–30], Siglec-7 greatly enhances either in its soluble form or as membrane receptor the susceptibility of CD4^pos cell targets expressing chemokine receptors to be infected by HIV-1, while spares from infection NK cells that, although positive for CCR5 or CXCR4, do not express CD4 [54].