ORAL MICROBIAL ECOLOGY AND THE ROLE OF SALIVARY IMMUNOGLOBULIN-A

In the oral cavity, indigenous bacteria are often associated with two major oral diseases, caries and periodontal diseases. These diseases s eem to appear following an inbalance in the oral resident microbiota, leading to the emergence of potentially pathogenic bacteria. To define the process involved in caries and periodontal diseases, it is necess ary to understand the ecology of the oral cavity and to identify the f actors responsible for the transition of the oral microbiota from a co mmensal to a pathogenic relationship with the host. The regulatory for ces influencing the oral ecosystem can be divided into three major cat egories: host related, microbe related, and external factors. Among ho st factors, secretory immunoglobulin A (SIgA) constitutes the main spe cific immune defense mechanism in saliva and may play an important rol e in the homeostasis of the oral microbiota. Naturally occurring SIgA antibodies that are reactive against a variety of indigenous bacteria are detectable in saliva. These antibodies may control the oral microb iota by reducing the adherence of bacteria to the oral mucosa and teet h. Ir is thought that protection against bacterial etiologic agents of caries and periodontal diseases could be conferred by the induction o f SIgA antibodies via the stimulation of the mucosal immune system. Ho wever, elucidation of the role of the SIgA immune system in controllin g the oral indigenous microbiota is a prerequisite for the development of effective vaccines against these diseases. The role of SIgA antibo dies in the acquisition and the regulation of the indigenous microbiot a is still controversial. Our review discusses the importance of SIgA among the multiple factors that control the oral microbiota. It descri bes the oral ecosystems, the principal factors that may control the or al microbiota, a basic knowledge of the secretory immune system, the b iological functions of SIgA, and, finally, experiments related to the role of SIgA in oral microbial ecology.