Dual secretion locations on type II cells in the avian lung suggest local as well as general roles of surfactant

Abstract

Transmission electron microscopy indicates that the avian lung surfactant may be secreted in two directions: a) into air passages of parabronchus, atrium and infundibulum where it forms a trilaminar substance serving the respiratory role and b) to the basolateral surface-intercellular space-of type II pneumocytes, contributing to the innate and adoptive immune responses of lung. Basolateral secretion may be confirmed by the presence of trilaminal substance in the intercellular space of type II pneumocytes. Fusion of surfactant containing vesicles with the lateral plasma membrane may result in membrane fusion of neighboring cells and subsequently formation of multinucleated giant cell. The indistinct and in some places discontinuous basal lamina in the parabronchial atrium and infundibulum permits the hydrophilic surfactant proteins to spread into the interstitium of air-blood capillary region. The hydrophilic surfactant proteins may activate lung interstitial macrophages to migrate into the air passages where they appear as "free avian respiratory macrophages." Therefore, in the interstitium the hydrophilic surfactant proteins are essential soluble components of innate immunity. J. Morphol. 277:1062-1071, 2016. © 2016 Wiley Periodicals, Inc.

A critical assessment of the cellular defences of the avian respiratory system: are birds in general and poultry in particular relatively more susceptible to pulmonary infections/afflictions?

“…While its possible role in defence has not been directly investigated in bird lungs (Van Iwaarden et al, 1990;Lorz & L opez, 1997;Kunchala et al, 2023), in the mammalian lung, together with functions such as reduction of surface tension (Van Golde, Batenburg & Robertson, 1988) and prevention of exudation of blood plasma onto the respiratory surface (Leiby, Raredon & Niklason, 2020), the surfactant provides an important defence function of destroying pathogenic microorganisms (Wright, 1997(Wright, , 2003Wu et al, 2003Wu et al, , 2021. For the lungs of the chicken, Stearns et al (1987) observed that inhaled particles were first trapped by the trilaminar substance, a special kind of avian pulmonary surfactant (Pattle, 1958;Tyler & Pangborn, 1964;Jones & Radnor, 1972;Scheuermann et al, 1997;B odi et al, 2016), and then moved across the epithelium to the underlying interstitial/subepithelial (tissue/fixed) macrophages and even across the BGB to be phagocytosed by the pulmonary intravascular macrophages (PIMs). The air sacs of the avian respiratory system are poorly vascularized, delicate and transparent (McLelland, 1989;Maina, 2005): the inner wall is predominantly lined by a simple squamous epithelium supported by a thin layer of connective tissue and scattered ciliated columnar cells that are located close to the ostial connections (Fletcher, 1980;McLelland, 1989;Crespo, Yamashiro & Hunter, 1998).…”

“…By serving as antigen-presenting cells, DCs regulate innate and adaptive immune responses (Albert, Sauter & Bhardwaj, 1998;Von Garnier & Nicod, 2009;Nicod, Cochand & Dreher, 2000;Banchereau et al, 2000;Soloff & Barratt-Boyes, 2010;Mokhtar & Hussien, 2019;Zmrhal & Slama, 2020;Chakraborty et al, 2022). In humans, DCs are involved in resisting infections, protection against cancers, organ transplant rejections and in production of T-cell-dependent antibodies (Bodey, Bodey & Kaiser, 1997;Vervelde et al, 2013;Zanna et al, 2021;Yue, Zhang & Sun, 2022). DCs are found in lymphoid organs such as bone marrow and thymus, peripheral lymphoid tissues such as spleen and lymph nodes, in most nonlymphoid organs and in all epithelial surfaces that interface with external environments, e.g.…”

“…For the lungs of the chicken, Stearns et al . (1987) observed that inhaled particles were first trapped by the trilaminar substance, a special kind of avian pulmonary surfactant (Pattle, 1958; Tyler & Pangborn, 1964; Jones & Radnor, 1972; Scheuermann et al ., 1997; Bódi et al ., 2016), and then moved across the epithelium to the underlying interstitial/subepithelial (tissue/fixed) macrophages and even across the BGB to be phagocytosed by the pulmonary intravascular macrophages (PIMs). The air sacs of the avian respiratory system are poorly vascularized, delicate and transparent (McLelland, 1989; Maina, 2005): the inner wall is predominantly lined by a simple squamous epithelium supported by a thin layer of connective tissue and scattered ciliated columnar cells that are located close to the ostial connections (Fletcher, 1980; McLelland, 1989; Crespo, Yamashiro & Hunter, 1998).…”