IDENTIFICATION OF A COMPLEMENT REGULATOR-ACQUIRING PROTEIN OF LEPTOSPIRA INTERROGANS

Angela Silva Barbosa (IBU); Ludmila Bezerra da Silva (IBU); Amane Paldès Gonçales (FMVZ-USP); Zenaide Maria de Morais (FMVZ-USP); Sílvio Arruda Vasconcellos (FMVZ-USP); Patrícia Antônia Estima Abreu (IBU)

Introduction: Leptospirosis is a spirochetal disease caused by pathogenic members of the genus Leptospira. After penetrating the host, leptospires have the ability to disseminate and to trigger a specific immune response. Their capacity to adhere to host cells and to escape the host´s innate immune defense systems contributes to colonization and persistence of those pathogens in the organism. A number of pathogenic microorganisms have evolved strategies to circumvent the immune defense systems of a variety of hosts, notably mechanisms to escape complement activation and/or lytic complement attack. Recently, we have shown that pathogenic leptospiral strains are able to bind C4b Binding Protein (C4BP). Surface-bound C4BP retains its cofactor activity, indicating that acquisition of this complement regulator may contribute to leptospiral serum resistance. Objectives: In the present study, the ability of six leptospiral recombinant proteins to interact with C4BP was evaluated by ligand affinity blot analyses. Methods and Results: One of them, named LepCRP (Leptospiral Complement Regulator Protein), interacted with this human complement regulator. Binding of LepCRP to C4BP was further examined by ELISA, and our results indicate that the recombinant protein exhibits a strong and saturable binding to C4BP. Triton X-114-solubilized extract of L. interrogans and phase partitioning showed that LepCRP was exclusively in the detergent phase, indicating that it is a component of the leptospiral membrane. The ability of both high- and low-passage in vitro cultured leptospires to express the gene coding for LepCRP was assessed by PCR amplification of reversely transcribed total RNA. Significant levels of transcripts could be only detected in low-passage strains. Discussion: This newly identified membrane protein may play a role in immune evasion of Leptospira.