Expression of surfactant Protein-A in the Haemophilus influenzae-induced otitis media in a rat model

The objective of this study was to investigate the expression and the role of surfactant protein A (SP-A) in the middle ear (ME) mucosa in response to bacterial infection in a rat model. Otitis media (OM) was induced by surgical inoculation of non-typeable Haemophilus influenza (NTHi) into the ME cavity of Sprague-Dawley rats. The rats were divided into an NTHi-induced OM group and a phosphate-buffered saline-injected control group. The NTHi-induced OM and control groups were subdivided into sets of 6 rats, one for each of the 6 time points (0, 1, 2, 4, 7, and 14 days post-inoculation), at which point the rats were euthanized after inoculation. The concentrations of SP-A in the ME effusion were determined by an enzyme-linked immunosorbent assay (ELISA). Tissue expression of SP-A, interleukin-1β (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α) in infected ME mucosa was assessed by immunohistochemical staining. For mRNA expression quantification, RNA was extracted from the ME mucosa and SP-A expression was monitored and compared between the control and OM groups using quantitative polymerase chain reaction (PCR). Expression of IL-1β, IL-6, and TNF-α in the ME mucosa was also evaluated. SP-A expression was evaluated in the effusion of pediatric OM patients (70 ears) who received ventilation-tube insertion by ELISA. SP-A was detected in normal rat ME mucosa before bacterial inoculation. SP-A expression was up-regulated in the NTHi-induced OM group (p = 0.046). Immunohistochemical staining revealed increased SP-A expression on post-inoculation day 1, 2, and 4 in the OM group. Expression of proinflammatory cytokines (IL-1β, IL-6, and TNF-α) in the ME also increased significantly on post-inoculation day 1, 2, and 4 in the OM group. It correlated with changes in SP-A expression. Expression of SP-A was also identified in the ME effusion of humans. SP-A exists in the ME of the rat and was up-regulated in the ME of NTHi-induced OM. Expression of IL-1β, IL-6, and TNF-α was increased in the ME of the bacteria-induced OM in the rat model. The results suggest that SP-A may play a significant role in the early phase of OM induction and subsequent recovery from it.