# The Heat Shock Protein 60 and Pap1 Participate in the _Sporothrix schenckii_-Host Interaction
## 4 Discussion
In agreement, a 62 kDa protein isolated from the _H. capsulatus_ cell wall, named HIS-62/Hsp60, was shown to play important roles during the interaction with the host, inducing T-cell activation and the stimulation of a protective immune response [36]. In addition, it contributes to fungal virulence due to its adhesive properties [37]. A similar observation was also reported for _P. brasiliensis_ Hsp60 [66; 90]. The fact that Pap1 was predicted to be an intrinsically disordered protein may offer a possible explanation for the wider ability to bind ECM components when compared to Hsp60. Gp70, besides being a highly immunogenic protein, is an _S. schenckii_ adhesin that mediates binding to the host dermal matrix and fibronectin [4; 91; 92]. However, unlike Hsp60 and Pap1, Gp70 is a typical cell wall protein with a signal peptide [93] and thus is likely to be transported by conventional secretion systems. Other putative adhesins for fibronectin, laminin, and type-II collagen in the _S. schenckii_ cell wall have been described, with variations among strains and morphologies [94; 95; 92; 95]. However, the identity of the proteins with those adhesive properties has not been established. When inoculated to _G. mellonella_ larvae before challenging with a lethal dose of _S. schenckii_ cells, both rHsp60 and rPap1 conferred protection against the experimental infection, and this observation resembles the immunological priming already reported in invertebrates, a response similar to the immunological memory found in the mammalian host and other vertebrates [96]. In _G. mellonella_, immunological priming was stimulated using bacteria, bacterial lipopolysaccharide, and _S. schenckii_ recombinant proteins [56; 61; 97; 98]. It was recently reported that a recombinant version of the _S. schenckii_ cell wall protein Gp70 stimulated immunological priming in _S. schenckii_ cells, increasing hemocyte levels and phenoloxidase activity [56]. As a consequence, increased survival rates of animals infected with _S. schenckii_ cells were observed [56]. Similarly, the inoculation of either rHsp60 or rPap1 stimulated immunological priming and reduced the mortality associated with the inoculation of the fungal cells, most likely due to the immunological activation by the recombinant proteins, allowing the animals to control fungal cells. This was supported by the low fungal burden and cytotoxicity observed in the hemolymph of infected animals. The fact that a lower dose of rPap1 was sufficient to generate these observations when compared to Hsp60 could be explained by the fact that the former is an intrinsically disordered protein and this could be an advantage to stimulate immune sensors involved in the immunological priming stimulation. This hypothesis remains to be addressed though. Our results here pave the way to assess the relevance of these proteins during the interaction with the mammalian host, such as the murine model of experimental sporotrichosis. One limitation we have to acknowledge about our experimental design is that it did not assess the contribution of the glycan moieties modifying Hsp60 and Pap1 during interaction with the host. However, nonglycosylated versions of the Gp70 are capable of stimulating a protective immune response in the murine model of infection caused by _S. brasiliensis_ and _S. globosa_[99; 100]. The clinically relevant species that cause sporotrichosis, _S. schenckii_, _S. brasiliensis_, and _S. globosa_ were reported to have different virulence profiles [2]. _S. brasiliensis_ was described as the most virulent species, and was associated with severe clinical forms of the mycosis, followed by _S. schenckii_ with moderate virulence, and _S. globosa_, considered a low-virulence species [2]. These different virulence profiles can be related to the virulence factors that the different species have, such as adhesins. Since the Hsp60 is a highly conserved protein, it was found in the three _Sporothrix_ species, while the Pap1 was found to be only present in _S. schenckii_ and _S. brasiliensis_ but not in _S.