COMPLEMENT SYSTEM ACTIVATION IN PATIENTS WITH HUMAN LEPTOSPIROSIS-ASSOCIATED SEVERE PULMONARY HEMORRHAGIC SYNDROME

• Grant number: 23/12968-1
• Support Opportunities: Scholarships in Brazil - Doctorate (Direct)
• Start date: April 01, 2024
• End date: October 31, 2026
• Field of knowledge: Biological Sciences - Immunology
• Principal Investigator: Lourdes Isaac
• Grantee: Milena Carvalho Carneiro
• Host Institution: Instituto de Ciências Biomédicas (ICB). Universidade de São Paulo (USP). São Paulo , SP, Brazil

Abstract

Leptospirosis is a neglected zoonosis, endemic in developing countries with tropical or subtropical climate. Approximately one million new cases are reported yearly with 5-10% deaths. Some patients develop a clinical condition called Leptospirosis- associated Severe Pulmonary Hemorrhagic Syndrome (LPHS), with a mortality rate higher than 50%. The etiopathology of LPHS remains to be elucidated. Some evidence suggests that its progression is multifactorial and may be due to: (1) leptospiral toxins that can damage blood capillaries, affect vascular permeability and allow the entry of a high number of bacteria into the tissues; and (2) an exacerbated immune response, causing a significant release of cytokines and anaphylatoxins that can affect tissue permeability, cause tissue damage and local hemorrhage.The deposition of C3 in the lungs of patients with LPHS has been previously reported, in human and animal models, suggesting that the activation of the Complement System may contribute to the hemorrhagic clinical picture. In these studies, the deposition of C3 was accompanied by the deposition of antibodies, indicating a possible activation of the Classical Pathway. However, the role of the Complement System in LPHS still needs to be further investigated.With this background, this study aims to evaluate the possible activation of the Complement System in patients who died from LPHS and identify the pathways involved in this process. For this, samples from dead LPHS patients (n=11) were used and compared to patients who died of sepsis (n=5) and acute myocardial infarction (n=5) (controls). Histopathological analysis was carried out in the lungs, kidneys and liver of the 3 groups.In the LPHS group, the lungs were observed to have a higher intensity of the hemorrhagic condition, higher incidence of septal inflammation, and formation of hyaline membrane. In the liver, moderate and intense dissociation of hepatocyte levels, lobular and portal inflammation, and necrosis were observed. Furthermore, there was greater tubular injury and mesangial hyperplasia in the kidneys when compared to the controls.Immunohistochemical assays were performed to analyze the deposition of Complement proteins: C1q, Factor B, MASP2, C3c, C4d, C5b-9 and the presence of anaphylatoxin receptors C3aR1 and C5aR, in the three study groups. At the same11time, immunoglobulins (IgG and IgM) deposition in the tissue and Leptospira antigens were evaluated.Preliminary results of the pulmonary analysis of patients with LPHS revealed the presence of C1q in the vascular endothelium, Factor B in the alveolar fibrin and lung epithelium, MASP2 in vascular endothelium and lung epithelium, and the Membrane Attack Complex (C5b-9) in the hyaline membranes, vascular endothelium, and apoptotic cells. So far, these results suggest that all three Complement pathways were activated in patients with LPHS. The quantification of C3c, C5aR, and IgM deposition in the alveolar septa didn't reveal a significant difference between the three groups; however, the analysis of other proteins is in progress. We believe that understanding the contribution of Complement in the etiopathogenesis of LPHS can guide the future use of inhibitors as a therapeutic treatment for LPHS patients.