Summary

• HIV virus type 1 (HIV-1) uses fusin as a cofactor, with CD4+cells in order to enter the cell.
• Fusin is a coupled coreceptor, G protein. It is a cofactor for T-tropic strains of the HIV virus.
• Certain chemokines inhibit cell fusion by inhibiting infection by M-tropic cell lines. This is done selectively through mediation by analogous envelope glycoproteins. These specific chemokines are RANTES, MIP-1a, AND MIP-1B.
• CC CKR5 is a recombinant coupled receptor, G protein for the aforementioned chemokines. CC CKR5 conferred CD4-expressing, nonhuman cells able to employ fusin preferentially with M-tropic envelope glycoproteins.
• CC CKR5 mRNA was selectively found in cells likely to be infected by M-tropic lines.
• This leads to the conclusion that CC CKR5 is a cofactor for M-tropic HIV-1 strains.

Questions/Purpose of Study

• To study the specific cytotropisms for infection of primary macrophages on HIV-1 isolates versus infectection on CD4+ T cell isolates. This cytotropism is determined by the corresponding envelope glycoprotein, where HIV binds. It is suggested that the cytotropism of the various isolates is a result of the inherent membrane fusion selectivities of the analogous envelope glycoproteins for different CD4+ target cell types.

Hypothesis

• Suppressive C-C chemokines exert infection-inhibition by binding to a chemokine receptor that acts as a fusion cofactor for M-tropic HIV-1 isolates, thus inhibiting fusion determined by the corresonding envelope glycoprotein.

Methods of Study

• Direct assays (vaccina-based) of fusion mediated recombinant envelope glycoproteins.
• Recombinant vaccina-based systems where fusion between envelope-expressing (Envs-expressing) and CD4-expressing cells causes expression of E. coli lacZ gene. Thus, B-galactosidase (B-gal) is produced in fused cells, selectively.
• Measurement of cell specificity with these assays
• Examination of effects of C-C chemokines on fusion reaction, using phytohemagglutinin PHA-activated peripheral blood mononuclear cells (PBMC's). ---used as the CD4+ target cell type.
• Comparison of envelope glycoproteins from prototypic M-tropic Ba-L isolate and T-tropic LAV isolate.
• Tested effects of C-C chemokines on fusion by CC CKR5 and CD4
• DNA probing
• Northern blot analysis

Results/Conclusions

• Recombinant CC CKR5 allowed nonhuman cells to go through fusion, mediated by Envs from M-tropic isolates.
• Inhibition of Ba-L Env-mediated fusion according to dose, in RANTES, MIP-1a, MIP1B, not in MCP-1, MCP-3
• The presence of a correspondence between CC CKR5 selectivity and specificity of chemokine inhibition of HIV infection and Env/CD4 determined cell fusion with human PBMCs and nonhuman cells coexpressing CC CKR5 and CD4.
• Differences in expression levels of different target cell molecules affects inhibition quantitatively.
• CC CKR5 and fusin are the only fusion cofactors for HIV-1 (One must also take into account the corresponding Envs.)

Future Studies/Connotations

• Practical applications in transgenic models of HIV-1 infection
• Possible treatment of HIV-1 infection
• Chemokines RANTES, MIP-1a, MIP-1B may have possible theraputic effects, as they are now known to have suppressive activity.