HIV type 1 Nef protein is a viral factor for leukocyte recruitment into the central nervous system

Recombinant HIV-1 Nef protein, but not Tat, gp120, and gp160, provoked leuk ocyte recruitment into the CNS in a rat model. The strong reduction of bioa ctivity by heat treatment of Net, and the blocking effect of the mAb 2H12, which recognizes the carboxyterminal amino acid (aa) residues 171-190 (but not of mAb 3E6, an anti-Nef Ab of the same isotype, which maps the aa seque nce 168-175, as well as a mixture of mAbs to CD4) provided evidence for the specificity of the observed Nef effects. Using a modified Boyden chamber t echnique, Nef exhibited chemotactic activity on mononuclear cells in vitro. Coadministration of the anti-Nef mAb 2H12, as well as treatment of Nef by heat inhibited Nef-induced chemotaxis. Besides soluble Nef, chemotaxis was also induced by a Nef-expressing human astrocytoma cell line, but not by co ntrol cells. These data suggest a direct chemotactic activity of soluble Ne f. The detection of elevated levels of IL-6, TNF-alpha, and IFN-gamma in ra t cerebrospinal fluid 6 h after intracisternal Nef injection hint at the ad ditional involvement of indirect mechanisms in Nef-induced leukocyte migrat ion into rat CNS, These data propose a mechanism by which HIV-1 Nef protein may be essential for AIDS neuropathogenesis, as a mediator of the recruitm ent of leukocytes that may serve as vehicles of the virus and perpetrators for disease through their production of neurotoxins.