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Zinc is a trace element that plays a central role in the immune system. In the present study, the effect of zinc on the phagocytic capacity of canine peripheral blood phagocytes was examined in vitro by flow cytometry. Zinc was used at a concentration of 100 μM, which preserved cell viability. Treatment with zinc did not directly affect the phagocytic capacity of peripheral blood polymorphonuclear neutrophils (PMN) and mononuclear cells (PBMC). However, it did directly enhance the phagocytic capacity of peripheral blood monocyte-rich cells. Moreover, the phagocytic capacity of PMN and monocyte-rich cells but not PBMC was remarkably enhanced by culture supernatants from PBMC but not PMN treated with zinc. Anti-recombinant canine (rc) tumor necrosis factor-alpha (TNF-α) polyclonal antibody (pAb) neutralized the enhancing effect of the culture supernatant from zinc-treated PBMC and this supernatant had higher TNF-α levels than the culture supernatant of untreated PBMC. Thus, zinc may stimulate canine PBMC to produce TNF-α, which enhances the phagocytic capacity of canine peripheral blood phagocytes.