Phagocytic and killing activity of human blood, gingival crevicular, and salivary polymorphonuclear leukocytes for oral streptococci.

The phagocytosis and killing of oral streptococci by blood, crevicular, and salivary polymorphonuclear leukocytes (PMNL) were examined using a visual assay based on differential staining of viable and non-viable microorganisms by acridine orange. Crevicular PMNL were 83% viable, 19% contained bacteria on collection, and phagocytosis occurred in vitro in 66% of glass-adherent leukocytes. Salivary PMNL were 56% viable, 11% contained bacteria on collection, and 44% phagocytosed streptococci in vitro. Crevicular and salivary PMNL were capable of phagocytosis and killing of oral streptococci, but both were impaired. Crevicular fluid was not significantly leukotoxic; mixed saliva caused a significant reduction in PMNL viability and in phagocytic and killing activity for oral streptococci. Crevicular PMNL may be actively functional phagocytes, but salivary PMNL are unlikely to be significant in oral defenses.