Correlation between kinetics of soluble CD4 interactions with HIV-1-Env-expressing cells and inhibition of syncytia formation: implications for mechanisms of cell fusion and therapy for AIDS.
OBJECTIVE
To study the kinetics of the interactions between soluble (s) CD4 and HIV-1-Env-expressing cells in relation to subsequent events leading to cell fusion and inhibition of syncytia formation.


METHODS
Vaccinia-HIV-1 (Env)-infected CD4- T-cells were used to study the kinetics of sCD4-gp120/41 interactions and syncytia formation (with CD4+ T-cells) under identical conditions.


METHODS
sCD4 association and dissociation rates for HIV-1-Env-expressing cells, and quantification of sCD4-induced gp120 shedding was determined by a quantitative flow cytometry assay. Syncytia inhibition was measured in the continuous presence of sCD4, or after washing of HIV-1-Env-expressing cells following pre-incubation with sCD4.


RESULTS
The kinetics of syncytia inhibition correlated with sCD4 binding when sCD4 was maintained during the culture. When Env-expressing cells, which had been pre-incubated with sCD4, were washed to remove unbound sCD4, no syncytia formation inhibition was observed, even following sCD4-induced shedding of greater than 50% of surface gp120 molecules.


CONCLUSIONS
The lack of syncytia inhibition seen after removal of unbound sCD4, even after pre-incubation of cells under saturation and gp120 shedding conditions, indicated that sufficient numbers of fusogenic molecules remained on the sCD4-treated cells. In addition, fast dissociation of pre-bound sCD4 occurred in culture. These results are important for understanding HIV-1-Env-mediated cell fusion and AIDS therapy.
Dimitrov
D S
DS
Section of Membrane Structure and Function, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892.
Hillman
K
K
Manischewitz
J
J
Blumenthal
R
R
Golding
H
H
D000163:Acquired Immunodeficiency Syndrome / Q000628:therapy; D000954:Antigens, Surface / Q000378:metabolism; D015704:CD4 Antigens / Q000378:metabolism*; D015496:CD4-Positive T-Lymphocytes / Q000166:cytology / Q000378:metabolism; D002460:Cell Line; D005434:Flow Cytometry; D015726:Giant Cells / Q000166:cytology / Q000378:metabolism; D015699:HIV Envelope Protein gp120 / Q000378:metabolism*; D015700:HIV Envelope Protein gp41 / Q000378:metabolism*; D015497:HIV-1 / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008561:Membrane Fusion / Q000502:physiology*
D000954:Antigens, Surface; D015704:CD4 Antigens; D015699:HIV Envelope Protein gp120; D015700:HIV Envelope Protein gp41