Innate Immunite and Inflammation

Abstract

A bacterium can find in the human oral cavity a variety of environmental niches that provide the warmth, moisture and food necessary for growth. Bacteria are able to invade this environment, adhere and colonize, gain access to food sources, and escape clearance by host nonimmune and immune responses thanks to genetic traits they have acquired. Unfortunately, diseases can be caused by many of the mechanisms the bacteria use to maintain their niches. This can occur either by destroying the tissue directly or indirectly, since the surface structures of the bacteria stimulate strong inflammatory host responses which can/may be protective but are often the main causes of the disease symptoms. The human body is colonized with numerous microbes as normal flora, many of which serve important functions for their hosts, such as protecting the host from colonization with pathogenic microbes. Therefore, not all bacteria cause disease. Almost 1000 microbial species have been identified in dental biofilm intimately integrated forming a consortia in which an interchange of nutrients and metabolic factors occurs. Genetic characteristics expressed by the biofilm let the microbial consortia to compete, cooperate, and survive a changing environment, resist antibiotics and acquire virulence factors to the detrimental of oral health. A “septic” gingival inflammation occurs when microbes and their virulence factors compromise the junctional epithelium health. Some of the natural defense mechanisms and physical and chemical barriers are salivary pH, mucus, secretions containing antibacterial substances such as lysozyme and collectins, phagocytic cells as neutrophils, macrophages and natural killer cells, blood proteins, including the complement system and other inflammatory mediators such as cytokines that regulate and coordinate the innate immune response.. The role of these factors is to make it difficult for the bacteria to enter the body. However, bacteria often have the means to compromise the epidermal barrier and invade the body. Initially gram-positive bacteria infects the mouth, while peptidoglycan and its breakdown products, teichoic and lipoteichoic acids, are released, which induce a pyrogenic acute-phase responses. New Gram-negative species, such as Porphyromonas gingivalis, Campylobacter rectus, Eikenella corrodens, Actinobacillus actinomycetemcomitans, and oral spirochetes (Treponema species) may be found present in the biofilm in the first four days following the beginning of plaque accumulation. While the dental plaque formation continues, Gram-negative species become dominant over the Gram-positive species. The overgrowth of Gram-negative anaerobic bacteria is considered one of the main causative factors that induce a complex sequence of events known as the inflammatory response of gingivitis. The lipopolysaccharide (LPS) produced by gram-negative bacteria is an even