ANAPHYLATOXIN C3A BUT NOT C3A(DESARG) IS A CHEMOTAXIN FOR THE MOUSE MACROPHAGE CELL-LINE J774

Varying results have been published regarding the functional reactivit y of different cell types, including human monocytes, to the anaphylat oxin C3a and its degradation product C3a(desArg). To further delineate the functions of C3a and C3a(desArg) on this cell type we used the mu rine macrophage (M empty set) cell line J774A.1 which is known to resp ond to the anaphylatoxin C5a. J774 cells specifically bound fluorescei n isothiocyanate-labeled recombinant human C3a (rCSa). The cells migra ted along rC3a concentration gradients in a dose-dependent manner with an optimal concentration of about 3 nM (rC5a: 7 nM) and a half-maxima l effective concentration (EC50) of about 1.2 nM (rC5a: 2 nM). The deg radation product rC3a(desArg) was devoid of chemotactic activity. mRNA for the recently cloned G protein-coupled mouse high-affinity C3a rec eptor (C3aR) was detected in J774 cells, suggesting that this receptor represents the binding site for C3a on J774 M empty set. In support o f the specific nature of C3a-stimulated cellular mobility, RBL-2H3 tra nsfectants expressing the human C3aR were also shown to migrate along gradients of rC3a (optimal concentration about 8 nM; EC50 about 3.5 nM ) whereas rCSa(desArg) was again inactive. In summary, our findings de monstrate for the first time a specific, receptor-mediated chemoattrac tion of cells of the monocytic lineage to the anaphylatoxin C3a which may contribute to the accumulation of M empty set at sites of inflamma tion.