Low-level laser therapy to the mouse femur enhances the fungicidal response of neutrophils against Paracoccidioides brasiliensis

Neutrophils (PMN) play a central role in host defense against the neglected fungal infection paracoccidioidomycosis (PCM), which is caused by the dimorphic fungus Paracoccidioides brasiliensis (Pb). PCM is of major importance, especially in Latin America, and its treatment relies on the use of antifungal drugs. However, the course of treatment is lengthy, leading to side effects and even development of fungal resistance. The goal of the study was to use low-level laser therapy (LLLT) to stimulate PMN to fight Pb in vivo. Swiss mice with subcutaneous air pouches were inoculated with a virulent strain of Pb or fungal cell wall components (Zymosan), and then received LLLT (780 nm; 50 mW; 12.5 J/cm2; 30 seconds per point, giving a total energy of 0.5 J per point) on alternate days at two points on each hind leg. The aim was to reach the bone marrow in the femur with light. Non-irradiated animals were used as controls. The number and viability of the PMN that migrated to the inoculation site was assessed, as well as their ability to synthesize proteins, produce reactive oxygen species (ROS) and their fungicidal activity. The highly pure PMN populations obtained after 10 days of infection were also subsequently cultured in the presence of Pb for trials of protein production, evaluation of mitochondrial activity, ROS production and quantification of viable fungi growth. PMN from mice that received LLLT were more active metabolically, had higher fungicidal activity against Pb in vivo and also in vitro. The kinetics of neutrophil protein production also correlated with a more activated state. LLLT may be a safe and non-invasive approach to deal with PCM infection.

PCM triggers a typical granulomatous inflammatory reaction with PMN playing a major role; these inflammatory cells are crucial in the initial stages of PCM, participating in the innate immune reaction and also directing the acquired immune response in the later stages. In some PCM patients, these immune mechanisms are insufficient to eradicate the infection, and need to be boosted with antifungal drugs that have to be administered for long periods and can show serious side-effects. We aimed to develop a novel and safe way to activate PMN through low-level laser irradiation of the bone marrow in the mouse femoral medulla. LLLT increased PMN viability and activation, shown by a significantly greater production of protein and ROS, as well as a higher fungicidal capacity; PMN even retained their higher metabolic activity and fungicidal ability after a second exposure to the pathogenic fungus in vitro. This is the first time that LLLT has been shown to increase the immune response against a fungal infection, and could be a promising and safe technique to be used with antifungal drugs in PCM.

Ultrastructural changes in Paracoccidioides brasiliensis yeast cells attenuated by gamma irradiation

Paracoccidioides brasiliensis is a thermally dimorphic fungus agent of paracoccidioidomycosis, a deep-seated systemic infection of humans with high prevalence in Latin America. Until now no vaccine has been reported. Ionizing radiation can be used to attenuate pathogens for vaccine development and we have successfully attenuated yeast cells of P. brasiliensis by gamma irradiation. The aim of the present study was to examine at ultrastructural level the effects of gamma irradiation attenuation on the morphology of P. brasiliensis yeast cells. Paracoccidioides brasiliensis (strain Pb-18) cultures were irradiated with a dose of 6.5 kGy. The irradiated cells were examined by scanning and also transmission electron microscopy. When examined 2 h after the irradiation by scanning electron microscopy, the 6.5 kGy irradiated cells presented deep folds or were collapsed. These lesions were reversible since when examined 48 h after irradiation the yeast had recovered the usual morphology. The transmission electron microscopy showed that the irradiated cells plasma membrane and cell wall were intact and preserved. Remarkable changes were found in the nucleus that was frequently in a very electrondense form. An extensive DNA fragmentation was produced by the gamma irradiation treatment.

Paracoccidioides brasiliensis: attenuation of yeast cells by gamma irradiation

Paracoccidioides brasiliensis is the agent of paracoccidioidomycosis, the most prevalent mycosis in Latin America, and currently there is no effective vaccine. The aim of this study was to attenuate the yeast form of P. brasiliensis by gamma irradiation for further studies on vaccine research. Paracoccidioides brasiliensis (strain Pb 18) cultures were irradiated at doses between 0.5 and 8.0 kGy. After each dose the viability, reproductive ability and protein metabolism were evaluated. The comparison between the antigenic profile of irradiated and control yeast was made by Western blot and the virulence evaluated by the inoculation in C(57)Bl/J6 mice. At 6.5 kGy the yeast lost its reproductive capacity. The viability and the incorporation of [L-(35)S]-methionine were the same in control and up to 6.5 kGy irradiated cells, but 6.5 kGy-irradiated yeast secreted 40% less proteins. The Western blot profile was clearly similar in control and 6.5 kGy-irradiated yeast. No colony-forming unit (CFU) could be recovered from the tissues of the mice infected with the radioattenuated yeast. We concluded that for P. brasiliensis yeast it is possible to find a dose in which the pathogen loses its reproductive ability and virulence, while retaining its viability, metabolic activity and the antigenic profile.