Deficiency of lung-specific claudin-18 leads to aggravated infection with Cryptococcus deneoformans through dysregulation of the microenvironment in lungs

Cryptococcus deneoformans is an opportunistic fungal pathogen that infects the lungs via airborne transmission and frequently causes fatal meningoencephalitis. Claudins (Cldns), a family of proteins with 27 members found in mammals, form the tight junctions within epithelial cell sheets. Cldn-4 and 18 are highly expressed in airway tissues, yet the roles of these claudins in respiratory infections have not been clarified. In the present study, we analyzed the roles of Cldn-4 and lung-specific Cldn-18 (luCldn-18) in host defense against C. deneoformans infection. luCldn-18-deficient mice exhibited increased susceptibility to pulmonary infection, while Cldn-4-deficient mice had normal fungal clearance. In luCldn-18-deficient mice, production of cytokines including IFN-gamma was significantly decreased compared to wild-type mice, although infiltration of inflammatory cells including CD4(+) T cells into the alveolar space was significantly increased. In addition, luCldn-18 deficiency led to high K+ ion concentrations in bronchoalveolar lavage fluids and also to alveolus acidification. The fungal replication was significantly enhanced both in acidic culture conditions and in the alveolar spaces of luCldn-18-deficient mice, compared with physiological pH conditions and those of wild-type mice, respectively. These results suggest that luCldn-18 may affect the clinical course of cryptococcal infection indirectly through dysregulation of the alveolar space microenvironment.

Automated summary

The lung-specific claudin-18 (luCldn-18) plays a crucial role in host defense against Cryptococcus deneoformans infection, as deficiency in luCldn-18 increases susceptibility to pulmonary infection. On the other hand, Cldn-4 does not have a significant role in fungal clearance. Deficiency in luCldn-18 leads to decreased cytokine production, increased inflammatory cell infiltration, acidification in the alveolar space, and enhanced fungal replication.