Complement system subversion by leptospires as a possible mechanism of renal immune evasion

Author(s)

Cassia Moreira Santos

• Document type: Master's Dissertation
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Faculdade de Medicina Veterinária e Zootecnia (FMVZ/SBD)
• Defense date: 2023-04-27

Examining board members

Ângela Silva Barbosa; Felipe Silva de França; Paula Carvalhal Lage von Buettner Ristow

• Advisor: Ângela Silva Barbosa

Abstract

Spirochetes belonging to the genus Leptospira are bacteria that cause leptospirosis. Highly mobile, pathogenic leptospires penetrate the host through skin abrasions or mucous membranes and rapidly reach target organs. The kidney is always considered an immunoprivileged site in leptospirosis, given persistence of these spirochetes in this organ. HK-2 renal cells produce complement proteins such as C3, Factor B and Factor H, in addition to molecules belonging to the other pathways of this system such as C1q, C2 and C4. Therefore, in this study, we evaluated whether L. interrogans serovar Manilae (L495), a pathogenic, virulent species, regularly kept in the laboratory as a study model, would be able to subvert the action of the alternative pathway of the complement system, inactivating locally produced molecules of the complement cascade. To this end, HK-2 cells were cultivated and infected with L. interrogans. According to our data, HK-2 infected cells synthesize greater amounts of C3, Factor B and Factor H. The C5 component was not detected in the supernatant of cells (infected or not). Leptospires acquire Factor H locally and this regulator remains functional, acting as a cofactor for Factor I in the inactivation of C3b, besides increasing the survival of these bacteria in Factor H depleted serum. In infected cells C3 was cleaved into C3a and C3b. While C3b is deposited on the bacteria, eventually acting as an opsonin, C3a accumulates in the supernatant over the incubation period. Interestingly, C3a levels are lower in the supernatant of infected cells compared to the control in the first 24 h of infection, leading us to speculate that this C3 fragment may eventually bind to its receptor on HK-2 cells. This hypothesis, as well as the consequences of this possible interaction, will be further investigated. In short, leptospires bind Factor H produced by HK-2 kidney cells and this negative regulator remains active. The complement system is locally activated in the presence of bacteria and its activation products may trigger a local inflammatory response related to the acute interstitial nephritis seen in leptospirosis. (AU)

• FAPESP's process: 21/00539-3 - Subversion of complement pathway by leptospires as possible immune evasion mechanism in the kidney
• Grantee: Cassia Moreira Santos
• Support Opportunities: Scholarships in Brazil - Master