The invasive and destructive behavior of HIV-induced T cell syncytia on collagen and endothelium

HIV-induced syncytia of the CD4⁺ SUP-T1 T cell line mimic the subcellular organization of single cells and are able to crawl like single cells through extension of giant pseudopods. Because syncytia have been demonstrated in lymphoid tissue of HIV-positive individuals, their behavior has been investigated on more natural substrata, including dehydrated collagen, hydrated collagen, endothelial monolayers, and endothelial monolayers grown on collagen cushions. On hydrated collagen gels, both individual SUPT1 cells and syncytia form unusually long cylindrical projections that possess pseudopodial ends and are highly dynamic. Syncytia penetrate collagen gels through extension of these projections and disrupt their integrity. When incubated on endothelium, both single cells and syncytia readily traverse the monolayer through holes, and when incubated on endothelium supported by a collagen cushion, syncytia generate large holes through the monolayer, penetrate the monolayer, and disrupt the collagen gel through extension of long, complex projections. Invading syncytia also release viruses in a polarized fashion which adhere to and are taken up in vesicles by the endothelium. It is suggested that the destructive behaviors of syncytia which have been demonstrated in vitro may have correlates in vivo.