DIFFERENTIAL ACTIVATION OF HUMAN NEUTROPHILS BY STREPTOCOCCUS-MUTANS ISOLATES FROM ROOT SURFACE LESIONS AND CARIES-FREE AND CARIES-ACTIVE SUBJECTS

Phagocytosis of bacterial pathogens is an important defense mechanism and may contribute to regulating Streptococcus mutans-induced dental c aries, particularly at root surfaces. This study was undertaken to exa mine and compare differences in polymorphonuclear leukocyte or neutrop hil activation by clinical isolates of S. mutans collected from the sa liva of caries-free or caries-active individuals with S. mutans isolat es from root surface lesions. S. mutans clinical isolates (5 caries-fr ee. 5 caries-active, 5 root caries isolates and a laboratory strain) w ere incubated with neutrophils in the presence of normal human serum a nd the luminol dependent chemiluminescence was measured for 1 h at 37 degrees C. Results indicated that the caries active and laboratory str ains activated neutrophils equally. The mean integration stimulated by caries-free strains, however, displayed a 25-30% enhanced neutrophil activation over the caries-active and laboratory strains. In contrast, neutrophil activation by root caries strains of S. mutans was 45-50% lower than all other S. mutans strains, possibly suggesting a natural selection for S. mutans strains that can evade neutrophil recognition and subsequent phagocytosis. stimulation of neutrophils with the cell wall and membrane surface component preparations indicated that extrac ts from all four groups activated neutrophils significantly. Again, ca ries-free preparations activated neutrophils significantly more than c aries active, laboratory strain and root caries isolates. This selecti on may become more important on root surfaces due to increased exposur e to crevicular fluid and neutrophils. The data provide evidence for t he presence or onset of mechanisms or biological alterations in S. mut ans developed to circumvent neutrophil recognition and/or phagocytosis , thus increasing S. mutans survival and colonization on tooth surface s, resulting in an enhanced risk of dental caries, particularly at roo t surfaces.