HIV-induced T-cell syncytia release a two component T-helper cell chemoattractant composed of Nef and Tat

Using a newly developed gradient chamber to provide independent measurement s of chemokinesis (stimulated motility) and chemotaxis (stimulated motility up a concentration gradient) of individual T-helper cells, it was recently demonstrated that HIV-induced T-cell syncytia release two distinct chemota ctic activities that are separable by their rates of diffusion. The molecul ar masses of the two chemoattractant activities were estimated to be 30 and 120 kDa. The higher molecular mass activity was demonstrated to be the vir al glycoprotein gp120, In an attempt to identify the lower molecular mass a ctivity, chemotaxis and chemokinesis of T-helper cells were analyzed in ind ividual concentration gradients of the virally encoded proteins Rev, p24, T at and Nef. None functioned alone as a chemoattractant, but both Tat and Ne f alone functioned as chemokinetic stimulants. When Tat and Nef were used t ogether to generate parallel gradients, they stimulated chemotaxis. Antibod y to either Tat or Nef neutralized the lower molecular mass chemotactic act ivity released by syncytia, The addition of antibody to the CD4 receptor or the addition of soluble CD4 inhibited high molecular mass chemotactic acti vity but not the low molecular mass chemotactic activity in HIV-induced syn cytium-conditioned medium, demonstrating that the former but not the latter activity is mediated through the CD4 receptor, These results identify the combination of Nef and Tat as the lower molecular mass T cell chemoattracta nt released by HIV-induced syncytia, and provide the first evidence suggest ing that parallel concentration gradients of two proteins are necessary for chemotaxis.