The Lung Responds to Zymosan in a Unique Manner Independent of Toll-Like Receptors, Complement, and Dectin-1

Abstract

In vitro studies indicate that the inflammatory response to zymosan, a fungal wall preparation, is dependent on Toll-like receptor (TLR) 2, and that this response is enhanced by the dectin-1 receptor. Complement may also play an important role in this inflammatory response. However, the relevance of these molecules within the in vivo pulmonary environment remains unknown. To examine pulmonary in vivo inflammatory responses of the lung to zymosan, zymosan was administered by intratracheal aerosolization to C57BL/6, TLR2- TLR4-, MyD88-, and complement-deficient mice. Outcomes included bronchoalveolar fluid cell counts. We next examined effects of dectin-1 inhibition on response to zymosan in alveolar macrophages in vitro and in lungs of C57BL/6, TLR2-, and complement-deficient mice. Finally, the effect of alveolar macrophage depletion on in vivo pulmonary responses was assessed. Marked zymosan-induced neutrophil responses were unaltered in TLR2-deficient mice despite a TLR2-dependent response seen with synthetic TLR2 agonists. TLR4, MyD88, and complement activation were not required for the inflammatory response to zymosan. Although dectin-1 receptor inhibition blocked the inflammatory response of alveolar macrophages to zymosan in vitro, in vivo pulmonary leukocyte recruitment was not altered even in the absence of TLR2 or complement. Depletion of alveolar macrophages did not affect the response to zymosan. Neither complement, macrophages, nor TLR2, TLR4, MyD88, and/or dectin-1 receptors were involved in the pulmonary in vivo inflammatory response to zymosan.

Characterisation of Innate Fungal Recognition in the Lung

“…As before, the inhibition of surfactant function with EDTA had no effect, even in the Dectin-1 deficient animals ( Figure 4A ). In contrast, and despite the convincing in vitro data (see Figure 1 ), we found that Dectin-1 was not essential for inflammatory responses to zymosan in vivo , even in the presence of EDTA ( Figure 4B ); a finding similar to that reported previously [22].…”

“…These data therefore suggest that there are other innate fungal recognition systems in the lung, which have yet to be defined, but may involve more recently identified receptors such as Dectin-2 [24] or Mincle [45]. A role for complement, TLR2, TLR4 and MyD88 has already been ruled out [22].…”

Severe neutrophil-mediated lung inflammation in myeloperoxidase-deficient mice exposed to zymosan

“…Intratracheal administration of zymosan has been shown to induce pulmonary inflammation in animal models [13]. It stimulates the oxidative burst in macrophages and neutrophils following internalization [14].…”

Overview of vertebrate animal models of fungal infection

“…These advances are likely to replace techniques that rely on surgical incision of the trachea for instillation of fungal cells [see videos in (Helms et al, 2010; Reddy et al, 2012)]. Dispersion of fungal cells into the pulmonary parenchyma may be enhanced by brief mechanical ventilation (Hasenberg et al, 2011) or by use of a microsprayer attached to the syringe tip (Kelly et al, 2008). The detergent Tween-20 is commonly used to prepare fungal cell suspensions for intranasal and intratracheal delivery.…”