Porcine TLR3 characterization and expression in response to influenza virus and Bordetella bronchiseptica.

We have provided a detailed structural analysis of porcine alveolar macrophage TLR3 extracellular domain (ECD). The porcine TLR3-ECD contains 18 leucine-rich repeats (LRRs) consisting of blocks of consensus motifs and non-consensus motifs containing insertions. Excluding the N-terminal and C-terminal LRRs, porcine TLR3 has two LRRs with insertions, resulting in one LRR of 39 amino acids and another LRR of 34 amino acids. Furthermore, we have conducted the first examination of the regulated expression of porcine alveolar macrophage TLR3 during in vivo co-infection with influenza virus and Bordetella bronchiseptica. There was a bi-phasic upregulation of porcine TLR3 during influenza virus infection (day 1 and day 10 post-infection). Co-infection resulted in an enhanced expression of porcine TLR3 only at day 1 post-infection. Interestingly, B. bronchiseptica induced an upregulation in alveolar macrophage TLR3 expression at day 10 post-infection. Based on our work and that of others, TLR3 likely plays a key role in the immune response of lung cells to influenza virus infection in several mammalian species.

Dendritic cell influx differs between the subglottic and glottic mucosae during acute laryngotracheitis induced by a broad spectrum of stimuli.

Clinically, the subglottic and glottic mucosae may react differently, eg, during acute laryngotracheitis. In healthy rats, we showed previously that the composition of the mucosal immune system of the larynx also differs between these areas. Neutrophils, lymphocytes, and dendritic cells (DCs) are part of this mucosal immune system. In particular, DCs occupy a key function. They migrate into inflamed mucosae during the early phase of the immune response, which is normally characterized by an influx of neutrophils. Thus, they help to overcome the time lag between the innate and the adaptive immune responses. In the present study, the influx of DCs, neutrophils, and T lymphocytes into the subglottic and glottic mucosae of rats was examined at different time points after challenge with a broad spectrum of stimuli such as dead Moraxella catarrhalis, viable Bordetella pertussis, viable Sendai virus, and the soluble protein ovalbumin. The number of DCs increased rapidly after the application of the antigens. This increase was as rapid as the increase in neutrophils. Depending on the kind of antigen, their number in the mucosa increased up to 1,000 cells per 0.1 mm2 (Sendai virus). The comparison of different mucosal areas shows that an overwhelming number of immunocompetent cells entered the subglottic mucosa, whereas only a few cells migrated into the adjacent glottic mucosa. In conclusion, after inhalation of different kinds of antigens, the subset of immunocompetent cells investigated in this study entered the laryngeal mucosa in high numbers. The number of DCs entering the laryngeal mucosa was higher than the numbers of the other immune cells investigated. This finding underlines their function as first-line sentinels of the mucosal immune system of the larynx. The observation that the number of cells entering the laryngeal mucosa is location-dependent indicates the ability of adjacent laryngeal regions to react differently. This is similar to the clinical observation of a selective subglottic reaction during acute laryngotracheitis.