Abstract
The surfaces of oral mucosa are protected from infections by antimicrobial proteins and natural immunoglobulins that are constantly secreted in saliva, serving as principal innate immune defense in the oral cavity. MyD88 is an important adaptor protein for signal transduction downstream of Toll-like receptors and TACI, receptors for regulation of innate immunity and B cell responses, respectively. Although MyD88-mediated signaling has a regulatory role in the intestinal mucosal immunity, its specific role in the oral cavity has remained elusive. In the present study, we assessed the influence of MyD88 deficiency on the oral innate defense, particularly the expression of antimicrobial proteins in salivary glands and production of salivary basal immunoglobulins, in mice. Microarray analysis of the whole tissues of submandibular glands revealed that the expression of several genes encoding salivary antimicrobial proteins, such as secretory leukocyte peptidase inhibitor (SLPI), S100A8, and lactotransferrin, was reduced due to MyD88 deficiency. Histologically, SLPI-expressing acinar cells were evidently decreased in the glands from MyD88 deficient mice compared to wild-type mice. Flow cytometric analysis revealed that B cell populations, including B-1 cells and IgA+ plasma cells, residing in submandibular glands were increased by MyD88 deficiency. The level of salivary anti-phosphorylcholine IgA was elevated in MyD88 deficient mice compared to wild-type mice. Thus, this study provides a detailed description of the effect of MyD88 deficiency on expression of several salivary antimicrobial factors in mice, illustrating the role for MyD88-mediated signaling in the innate immune defense in the oral cavity.
Highlights
Saliva, which is secreted from the salivary glands (SGs), is one of the major body fluids
To determine the effect of MyD88 deficiency on the oral innate defense, we focused on the major SGs because they are major sources of various salivary antimicrobial products
We initially evaluated the histological appearance of SGs collected from naive Myd88-/- mice as well as Myd88+/+ control mice
Summary
Saliva, which is secreted from the salivary glands (SGs), is one of the major body fluids. The lubricative function of saliva is important for protection of the oral mucosal surfaces from desiccation, wetting foods and facilitating the initiation of swallowing. The salivary digestive enzymes are essential in the processing of dietary starches and fats. Antimicrobial agents are contained in saliva, constantly protecting the surfaces of oral mucosa from infections. A variety of antimicrobial proteins (AMPs), including bactericidal peptides and enzymes, and natural immunoglobulins (Igs), including IgA and IgM, are constantly secreted [1,2,3]. They are thought to serve as the principal innate immune defense in the oral cavity
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