Complex inositol polyphosphate response induced by co-cross-linking of CD4 and Fc gamma receptors in the human monocytoid cell line U937.
The cell-surface Ag CD4, which is characteristic for Th lymphocytes, can also be found with a lower density on monocytes/macrophages. Co-cross-linking of CD4 and Fc gamma R by an anti-CD4 mAb (MAX.16H5) and by excess of goat anti-mouse Ig induced a biphasic increase of the free cytosolic Ca(2+)-concentration ([Ca2+]i) in the human monocytoid cell line U937 as measured by FURA-2 fluorescence. A rapid rise from 100 to 150 nM [Ca2+]i to 750 to 900 nM within 1 min was followed by a decline to about 200 to 300 nM within the next 2 to 3 min. This kinetic is characteristic also for blood monocytes and differs significantly from CD4-mediated Ca(2+)-mobilization in T lymphocytes. The rise in [Ca2+]i in U937 cells was not observed when F(ab)2 fragments of MAX.16H5 and F(ab)2 fragments of the cross-linker were used indicating the involvement of Fc gamma R. Time course analysis using HPLC and a recently developed post-column dye system for mass analysis revealed a complex inositol polyphosphate response with rapid increases not only in inositol 1,4,5-trisphosphate and inositol 1,3,4,5-tetrakisphosphate, but also in D/L-inositol 1,4,5,6-tetrakisphosphate, inositol 1,3,4,5,6-pentakisphosphate, and inositol hexakisphosphate after co-cross-linking of CD4 and Fc gamma R. In conclusion, co-cross-linking of CD4 and Fc gamma R, which may occur in vivo during HIV infection or treatment with therapeutic anti-CD4 antibodies, appears to be a strong activation mechanism for the inositol polyphosphate/Ca2+ signal transduction pathway in U937 cells.
Guse
A H
AH
Max-Planck-Society, Institute for Clinical Immunology of the University, Erlangen, Germany.
Roth
E
E
Bröker
B M
BM
Emmrich
F
F
D000943:Antigens, Differentiation / Q000502:physiology*; D015704:CD4 Antigens / Q000032:analysis / Q000502:physiology*; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D006801:Humans; D007074:Immunoglobulin G / Q000378:metabolism*; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D007295:Inositol Phosphates / Q000378:metabolism*; D009000:Monocytes / Q000378:metabolism*; D011961:Receptors, Fc / Q000502:physiology*; D017452:Receptors, IgG
D000943:Antigens, Differentiation; D015704:CD4 Antigens; D007074:Immunoglobulin G; D007295:Inositol Phosphates; D011961:Receptors, Fc; D017452:Receptors, IgG; C081655:inositol-1,3,4,5-tetrakisphosphate; C081651:inositol-1,4,5,6-tetrakisphosphate; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium