Evaluation of the pathophysiological mechanisms involved in pediatric sepsis susceptibility and its long-term consequences

Author(s)

David Fernando Colón Morelo

• Document type: Doctoral Thesis
• Press: Ribeirão Preto.
• Institution: Universidade de São Paulo (USP). Faculdade de Medicina de Ribeirão Preto (PCARP/BC)
• Defense date: 2020-06-22

Examining board members

Fernando de Queiroz Cunha; Larissa Dias da Cunha; João Santana da Silva; Mauro Martins Teixeira

• Advisor: Fernando de Queiroz Cunha

Abstract

Sepsis is one of the leading causes of mortality in hospitalized patients worldwide. Clinically it is defined as a potentially fatal organ dysfunction caused by the dysregulated immune response to infection. It is noteworthy that infants are an age group particularly susceptible to sepsis, presenting a higher risk of mortality when compared to the adult population; Nevertheless, the mechanisms that explain this high susceptibility have been poorly studied. In addition to sepsis severity, adult sepsis survivors commonly develop a long-term immunosuppression associated with the increased susceptibility to secondary infections, which might last for up to five years. Conversely, the investigation of the long-term immune consequences of sepsis in the pediatric population have been neglected. Hence, the objective of the present study was to study the pathophysiological mechanisms involved in the susceptibility of infant to sepsis as well as the immunomolecular mechanisms involved in the late consequences of sepsis in surviving infant individuals. We found that, similar to epidemiological observations regarding pediatric sepsis, infant mice are more susceptible to sepsis when compared to adults. Remarkably, we found that this high susceptibility was due to the high production of NETs (Neutrophils Extracellular Traps) both in vitro and in vivo, associated with the increase of Padi4 expression and histone H3 citrunylation in the tissues. Moreover, it was found that the systemic degradation of NETs, using rhDNase associated with antibiotic therapy or through pharmacological inhibition of the Pad4 enzyme, significantly increased the survival of infant mice to sepsis, which was related with a reduction in systemic inflammation markers and organ damage. Notably, in a translational manner, we found that pediatric patients exhibit higher serum NET concentrations compared to adult patients, and the serum levels of NET were positively correlate with the severity of pediatric sepsis. Nevertheless, despite the high susceptibility to the acute phase of sepsis, unlike previously reported in adult individuals, we demonstrated that sepsis-surviving infant mice do not develop late immunosuppression. Specifically, sepsis-surviving infant mice were resistant to P. aeruginosa-induced secondary infection as well as showing no changes in T-cell-dependent tumor immunovigilance when compared to adults. Mechanistically, we found that this \"resistance\" to the development of immunosuppression was associated with the reduction in the IL-33 / ILC2 axis, M2 / Tregs profile macrophages axis activation as well as the high degree of DNA methylation in pulmonary epithelial cells and TCD4+CD25- cells of infant surviving mice. Likewise, Tregs cells from infant mice showed less stability in Foxp3 expression. In order to transfer our findings to human settings, we demonstrated that sepsis- surviving pediatric patients did not show Tregs cell expansion or increase in serum IL-33 levels when compared to adults. In conclusion, we have shown that, even though in the acute phase of sepsis, infants are highly susceptible; after the septic process, sepsis-surviving mice are resistant to the development of long-term immune dysfunction resulting from sepsis, suggesting that long-term immunosuppression after to sepsis is an age-dependent phenomenon. (AU)

• FAPESP's process: 16/11405-0 - Immuno-molecular mechanisms involved in the resistance to the development of immunosuppression in neonatal sepsis
• Grantee: David Fernando Colon Morelo
• Support Opportunities: Scholarships in Brazil - Doctorate