Abstract
Salivary immunoglobulin A (IgA) plays a critical role in mucosal immunity. Chronic exposure to moderate heat induces heat acclimation, which modifies salivary functions. However, the changes in salivary IgA secretion in heat-acclimated rats are unclear. In this study, we investigated salivary IgA secretion and the expression of polymeric Ig receptor (pIgR), a key mediator of mucosal IgA secretion, in the submandibular glands (SMGs) of heat-acclimated rats. Following maintenance at an ambient temperature (Ta) of 24 ± 0.1 °C for 10 days, male Wistar rats were subjected to Ta of 32 ± 0.2 °C for 5 days (HE group) for heat acclimation or maintained at Ta of 24 ± 0.1°C (CN group). The rats were then anesthetized, pilocarpine (0.5 mg/kg) was intraperitoneally injected, and saliva was collected. Afterward, the SMGs and plasma were sampled. The salivary IgA concentration and IgA flow rate were significantly higher in the HE group than in the CN group. Similarly, SMG pIgR expression was significantly higher in HE rats. The levels of plasma cytokines, including interleukin (IL)-5, IL-6, and interferon-γ, were significantly greater in HE rats than in CN rats. Heat acclimation may enhance oral immunity through salivary IgA secretion and pIgR upregulation in the SMGs.
Highlights
Immunoglobulin A (IgA) is a type of antibody that mainly functions in the mucosal immune system and serves as the first line of defense in protecting the oral cavity and upper respiratory tract [1,2]
We found that the salivary IgA concentration and IgA flow rate were significantly increased in heat-acclimated rats
Salivary IgA secretion increased in the first 2 days of the heat exposure period and remained elevated for at least 14 days. These results suggest that salivary IgA secretion may be promoted by polymeric immunoglobulin receptor (pIgR) upregulation in the submandibular glands (SMGs) of heat-acclimated rats
Summary
Immunoglobulin A (IgA) is a type of antibody that mainly functions in the mucosal immune system and serves as the first line of defense in protecting the oral cavity and upper respiratory tract [1,2]. DIgA binds the polymeric immunoglobulin receptor (pIgR) on the basolateral surface of epithelial cells and forms the IgA-pIgR complex. The IgA-pIgR complex is transported to the lumen from the basolateral surface. A fragment of pIgR becomes a secretory component (SC) that binds dIgA. In this manner, secretory IgA (sIgA) combines with other SCs, and free SCs are released. SIgA binds to luminal bacteria and prevents them from accessing the epithelial surface [4,5]. A reduction in salivary sIgA levels grants bacteria access to the epithelial surface and leads to various diseases such as upper respiratory tract infection and periodontal disease [6,7]
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