Re-infections with Trypanosoma cruzi are an aggravating factor for Chagas disease morbidity. The Colombian strain of T. cruzi represents multiclonal populations formed by clonally propagating organisms with different tropisms and degrees of virulence. In the present study, the influence of successive inoculations with clones of the Colombian strain, exhibiting different degrees of virulence, on chronic myocarditis and the humoral and cellular immune responses (Col-C1 high virulence, Col-C8 medium virulence and Col-C5 low virulence) were demonstrated. Mice from three groups with a single infection were evaluated during the acute (14th-30th day) and chronic phases for 175 days. An immunofluorescence assay, ELISA and delayed type hypersensitivity (DTH) cutaneous test were also performed. Mice with a triple infection were studied on the 115th-175th days following first inoculation. The levels of IgM and IgG2a were higher in the animals with a triple infection. DTH showed a higher intensity in the inflammatory infiltrate based on the morphometric analysis during a 48 h period of the triple infection and at 24 h with a single infection. The histopathology of the heart demonstrated significant exacerbation of cardiac inflammatory lesions confirmed by the morphometric test. The humoral responses indicate a reaction to the triple infection, even with clones of the same strain.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the virus responsible for coronavirus 2019 , which was declared a pandemic in March 2020 by the World Health Organization due the rapid spread representing a global health crisis. The disease is characterized by a wide clinical spectrum ranging from asymptomatic forms until severe viral pneumonia, which can to evolve to severe acute respiratory syndrome, especially in elderly patients and/or with comorbidities. An efficient assembly of the immunological response of the patients becomes fundamental against SARS-CoV-2 infection and it has been demonstrating a significant relationship between the severity of the disease and expression profile of the immune cells and the levels of pro-inflammatory cytokines. This review aims to presents the main immunological mechanisms developed during the infection by SARS-CoV-2 in the evolution of the severe cases of COVID-19. The immune dysregulation of the Th1 cellular response standard, the instability in the production of neutralizing antibodies by plasma B cells, the difference in tropism of CD8+ T cells against virus proteins in early infection, late infection and reinfections, dynamic of alveolar macrophages and pulmonary innate lymphoid cells (TCR γδ) of the natural imune response and the high level of pro-inflammatory cytokines can determine the main cause of breath tissues damages and, consequently, a greater severity of the disease. Therefore, a complete understanding of the main immunological changes involved in SARS-CoV-2 infection can identify possible biomarkers in the evaluation of early prognosis of the severe cases of COVID-19, making possible better therapeutic success to the patients.