Study of the PTX3 activity in the pulmonary inflammatory response in a murine model.

Innate immunity plays key roles in activation and orientation of adaptive immunity and consists of a cellular and a humoral arm. The humoral arm is composed by a heterogeneous collection of weird molecules that represent functional ancestors of antibodies and form an integrated system of diverse molecules, including collectins, ficolins, and pentraxins (1). Pentraxins constitute a superfamily of multifunctional multimeric proteins and Pentraxin-3 (PTX3) is the first member of the long pentraxin subfamily. It is released from dendritic cells, mononuclear phagocytes, fibroblasts, endothelial and epithelial cells upon exposure to inflammatory signals such as cytokines (e.g. IL-1β, TNF-α), TLR agonists, microbial moieties (e.g. LPS, OmpA) or microorganisms (1,2). PTX3 acts as an opsonin, binding the bacteria to facilitate their phagocytosis by the DCs and macrophages. On these bases, we investigated the role of PTX3 during a pulmonary infection by Shigella flexneri, in mouse. For this purpose, C57Bl/6 mice were inoculated intranasally with 20 μl of 0.9% NaCl suspensions containing 3X10⁸ CFU of the strain. Control mice were similarly inoculated with 20 μl of PBS. At the same time, PTX3 were administered via ip route once per day for three consecutive days following challenge. We monitored animals for mortality and clinical signs. After 72 h post-infection, mice were euthanatized and lungs and BALF were collected and processed for histopathological studies, and macrophage analysis. We analyzed the inflammatory response and tissue damage in lungs through histological evaluation and immunohistochemistry analysis. In order to characterize the cell-mediated response in T-cell population, tissue were tested with different primary antibody by immunohistochemistry staining. Moreover we performed in vitro macrophage activity assays, following primary culture by BALF, evaluating phagocytosis and respiratory burst. The intranasal infection resulted in bacterial invasion of bronchial and alveolar epithelia with concomitant development of acute suppurative bronchiolitis and lethal pneumonia. Infected mice lungs showed acute bronchiolitis with diffuse alveolar damage, exuberant neutrophilic exudate and peribronchiolar and interstitial inflammatory infiltrate. Mice treated with PTX3 showed particularly activation of BALT and increased macrophage activity. Our results show that in the mouse, PTX3 modulates the inflammatory response by reducing the acute phase, stimulating activation of the BALT and then leading a cell-mediated response.