We report here canine mastocytoma-derived cell (CMMC) activation via two pentraxin, limulus- and human-CRP. Mast cell chemotaxis was measured by Boyden's blindwell chamber. To confirm that the cell migration was chemotactic, "checkerboard" analysis was performed. We used Fura-2 to investigate CRP-mediated cytosolic calcium elevation. To examine whether CRP-induced stimulation is mediated through G-proteins, CMMC were incubated with pertussis toxin (PTx) before use in chemotaxis assay and Ca2+ mobilization. CMMC migration in response to CRP was both chemokinetic and chemotactic. Limulus-CRP induced a transient Ca2+-mobilization dose-dependently. Preincubation of the cells with PTx inhibited CRP chemotaxis and Ca2+-mobilization, suggesting that G-proteins of the Gi-class are involved in the chemotaxis. We suggest that CRP may participate in the migration of mast cells to inflamed tissues during an acute-phase response. CRP-mediated recruitment of mast cells might play an important role in hypersensitivity and inflammatory processes. (C) 2002 Elsevier Science (USA). All rights reserved.