Pseudomonas aeruginosa Infection Modulates the Immune Response and Increases Mice Resistance to Cryptococcus gattii

Abstract

Cryptococcosis is an invasive mycosis caused by Cryptococcus spp. that affects the lungs and the central nervous system (CNS). Due to the severity of the disease, it may occur concomitantly with other pathogens, as a coinfection. Pseudomonas aeruginosa (Pa), an opportunistic pathogen, can also cause pneumonia. In this work, we studied the interaction of C. gattii (Cg) and Pa, both in vitro and in vivo. Pa reduced growth of Cg by the secretion of inhibitory molecules in vitro. Macrophages previously stimulated with Pa presented increased fungicidal activity. In vivo, previous Pa infection reduced morbidity and delayed the lethality due to cryptococcosis. This phenotype was correlated with the decreased fungal burden in the lungs and brain, showing a delay of Cg translocation to the CNS. Also, there was increased production of IL-1β, CXCL-1, and IL-10, together with the influx of iNOS-positive macrophages and neutrophils to the lungs. Altogether, Pa turned the lung into a hostile environment to the growth of a secondary pathogen, making it difficult for the fungus to translocate to the CNS. Further, iNOS inhibition reverted the Pa protective phenotype, suggesting its important role in the coinfection. Altogether, the primary Pa infection leads to balanced pro-inflammatory and anti-inflammatory responses during Cg infection. This response provided better control of cryptococcosis and was decisive for the mild evolution of the disease and prolonged survival of coinfected mice in a mechanism dependent on iNOS.

Secondary Streptococcus pneumoniae infection increases morbidity and mortality during murine cryptococcosis

“…Fragments of lung tissues were used to determine myeloperoxidase (MPO) and N ‐acetylglucosaminidase (NAG) activities, providing an indirect measurement of neutrophil and macrophage influx, respectively, as previously described [13]. In addition, levels of IL‐1β, TNF, IFN‐γ, IL‐17 and IL 12p70 were quantified in BALF and lungs by ELISA according to the manufacturer's guidelines (R&D System, Minneapolis, MN) [24].…”

“…Then, colonies were suspended in Phosphate Buffered Saline (PBS), and cells were counted in a Neubauer Chamber. The concentration of viable cells was obtained after Trypan Blue staining [13]. Finally, for fungal infection, mice were inoculated intratracheally (i.t.)…”

“…Finally, for fungal infection, mice were inoculated intratracheally (i.t.) with 10 4 CFU of Cg in 30 μL of PBS [13].…”

“…Coinfections are infections caused by two or more microorganisms, which may present synergistically or sequentially [13, 14]. The problem in these conditions is that the first infection modifies immunity and pathology to the secondary one [13, 15–18].…”

“…Coinfections are infections caused by two or more microorganisms, which may present synergistically or sequentially [13,14].The problem in these conditions is that the first infection modifies immunity and pathology to the secondary one [13,[15][16][17][18]. For instance, previous infection by Influenza A virus facilitates the colonization and infection by both S. pneumoniae and C. gattii, contributing to the development of more severe infections [19,20].…”