Autoimmunity may have its origins of early repertoire selection in developmental B cells. Such a primary repertoire is probably shaped by selecting B cells that can efficiently perform productive signaling, stimulated by self-antigens in the bone marrow, such as DNA. In support of that idea, we previously found a V segment from VH10 family that can form antibodies that bind to DNA independent of CDR3 usage. In this paper we designed four antibody fragments in a novel single-chain pre-BCR (scpre-BCR) format containing germinal V gene segments from families known to bind DNA (VH10) or not (VH4) connected to a murine surrogate light chain (SLC), lacking the highly charged unique region (UR), by a hydrophilic peptide linker. We also tested the influence of CDR2 on DNA reactivity by shuffling the CDR2 loop. The scpre-BCRs were expressed in bacteria. VH10 bearing scpre-BCR could bind DNA, while scpre-BCR carrying the VH4 segment did not. The CDR2 loop shuffling hampered VH10 reactivity while displaying a gain-of-function in the nonbinding VH4 germline. We modeled the binding sites demonstrating the conservation of a positivity charged pocket in the VH10 CDR2 as the possible cross-reactive structural element. We presented evidence of DNA reactivity hardwired in a V gene, suggesting a structural mechanism for innate autoreactivity. Therefore, while autoreactivity to DNA can lead to autoimmunity, efficiently signaling for B cell development is likely a trade-off mechanism leading to the selection of potentially autoreactive repertoires.

Queria agradecer aos meus pais, Francisco da Chagas e Eliane Maria pelo apoio, suporte e compreensão durante toda a vida. Ao Professor Marcelo Brígido e a Professora Andrea Maranhão pela oportunidade que me foi dada, pela confiança e pelos ensinamentos que com certeza me ajudaram amadurecer ainda mais. Ao Professor Napoleão Valadares pelas dicas valiosas e por ceder os equipamentos necessários para o desenvolvimento de alguns experimentos. Aos meus irmãos, Emerson Chagas, Danielle Araujo e Ingridy Juliana pelo companheirismo ao longo dos anos. Aos meus familiares de Brasília Tia Leila, meus primos Marcos Henrique e Helder Castro, meu avô e sua esposa, Dona Aparecida) que me receberam de braços abertos quando iniciei essa nova etapa, tornando essa transição bem mais fácil e agradável.Aos meus amigos e companheiros de laboratório durante esses anos,