Immune response of macrophages from young and aged mice to the oral pathogenic bacterium Porphyromonas gingivalis

As humans age, they become more susceptible to a variety of infections including those of the lung, urinary tract, and skin [1]. This increase in infection results in concomitant increase in morbidity and mortality for elderly individuals [1]. The mechanisms underlying age-dependent increase in susceptibility to infection are complex, though decline in immune function and immune senescence is thought to play a central role [2]. Age-related changes in immune fitness have been identified in both the adaptive and innate arms. Effects associated with aging on adaptive immunity include diminished capacity of cells to present antigen, as well as reduced capacity to generate antigen-specific T and B cells [3,4]. Changes in innate immune response include capacity to recognize and respond to pathogens, which may be in part as a result of reduced expression of cell surface receptors, such as the Toll-like receptors (TLRs) [5]. TLRs are a family of receptors that bind conserved microbial structures shared by large groups of pathogens, termed pathogen-associated molecular patterns. Ligation of these receptors with specific pathogen derived antigens initiates intracellular signaling that culminates in coordinated expression of genes that encode molecules such as cytokines and chemokines [6]. Cytokines and chemokines serve diverse roles in many host functions including cell activation, immune function, and communication as well as cell recruitment. Aberrant production of cytokines and chemokines has been observed in aged individuals as compared with young [7].Periodontal disease is a common chronic oral inflammatory disease [8]. Although complex in pathogenesis, it is commonly thought that erosion of the soft and hard tissue supporting teeth results from bacteria-elicited inflammation. Among the various bacterial species associated with the development of periodontitis, Porphyromonas gingivalis (Pg), a Gram-negative anaerobic bacterium suspected to be one of the most important ca