A influência da infecção por MHV-A59 na reposta imune adaptativa e seu impacto na infecção murina por Candida albicans

Abstract

COVID-19 is an infectious disease caused by the SARS-CoV-2 virus that has led to a pandemic and has resulted in a high number of deaths and comorbidities. Vaccination against SARS-CoV-2 has contributed to reduce the number of deaths. However, it has been observed that patients infected with COVID-19 may have persistent symptoms despite vaccination or may develop new symptoms after recovery from the disease. This late-onset symptomatology is referred to as long COVID, although the immune mechanisms responsible for long COVID are not yet fully understood. In order to assess susceptibility to worsening in a subsequent infection, in the context of long COVID, we chose to use Candida albicans in our evaluations. C. albicans is a fungus of great clinical importance, with a high incidence in opportunistic infectious contexts, including infections caused by SARS-CoV-2. Our aim was therefore to investigate whether changes in the activation profile of T lymphocytes induced by coronavirus infection in mice influence host susceptibility to Candida albicans infection. To this end, we used an in vivo infection model in which we infected female C57BL/6 mice with MHV-A59 by intranasal administration and initially examined two infection time points. In the first experiment, the mice were infected with MHV-A59 and infected with C. albicans after seven days and euthanized two days after C. albicans infection. In another experiment with a later infection time point, the animals were pre-infected with MHV-A59 and infected with C. albicans after twenty-one days and euthanized two days after C. albicans infection. Bronchoalveolar lavage was collected for analysis of fungal utilization and evaluation of the T-cell profile by flow cytometry. Lungs were harvested for histopathologic analysis, analysis of fungal and viral debris, assessment of T-cell activation profile, assessment of neutrophil activity, and quantification of cytokines. We also examined the lung function of the animals at later time points using spirometry. In our histopathologic analyzes, we demonstrated that C. albicans infection led to an increase in inflammatory infiltrates seven days after MHV-A59 infection. However, when the animals were infected with C. albicans twenty-one days after MHV-A59 infection, they showed a significant loss of lung tissue structure. Our results showed that infection with C. albicans or MHV-A59 alone was not sufficient to cause an increase in lymphocytes. However, the group exposed to both infections showed an increase in CD8+ T cells. Nevertheless, the groups infected only with C. albicans showed an increase in regulatory T cells compared to the groups infected first with MHV-A59 and then with C. albicans. These results suggest that the inability of the host to develop a regulatory response against secondary infection is a key factor. Interestingly, we observed that MHV-A59 infection did not affect the clearance of C. albicans or induce changes in neutrophil activity, despite the changes in cellular profile. We also examined the lung function of animals infected with C. albicans twenty-one days after MHV-A59 infection and euthanized two and nine days after C. albicans infection. Our results showed pulmonary dysfunction after nine days of C. albicans infection, with changes in parameters related to increased airflow and pulmonary hyperinflation consistent with findings in chronic obstructive pulmonary disease (COPD). In summary, these results suggest that MHV A59 infection in response to secondary C. albicans infection triggers an increase in effector T cells without adequate regulation by regulatory T cells, leading to lung damage and impaired lung function.