BackgroundToxoplasma gondii is an intracellular parasite that causes relevant clinical disease in humans and animals. Several studies have been performed in order to understand the interactions between proteins of the parasite and host cells. SAG2A is a 22 kDa protein that is mainly found in the surface of tachyzoites. In the present work, our aim was to correlate the predicted three-dimensional structure of this protein with the immune system of infected hosts.MethodsTo accomplish our goals, we performed in silico analysis of the amino acid sequence of SAG2A, correlating the predictions with in vitro stimulation of antigen presenting cells and serological assays.ResultsStructure modeling predicts that SAG2A protein possesses an unfolded C-terminal end, which varies its conformation within distinct strain types of T. gondii. This structure within the protein shelters a known B-cell immunodominant epitope, which presents low identity with its closest phyllogenetically related protein, an orthologue predicted in Neospora caninum. In agreement with the in silico observations, sera of known T. gondii infected mice and goats recognized recombinant SAG2A, whereas no serological cross-reactivity was observed with samples from N. caninum animals. Additionally, the C-terminal end of the protein was able to down-modulate pro-inflammatory responses of activated macrophages and dendritic cells.ConclusionsAltogether, we demonstrate herein that recombinant SAG2A protein from T. gondii is immunologically relevant in the host-parasite interface and may be targeted in therapeutic and diagnostic procedures designed against the infection.
The specificity of monoclonal antibodies (mAbs) to desired targets makes these molecules suitable for therapeutic and diagnostic uses against a wide range of pathogens. Phage display antibody libraries offer one method by which mAbs can be selected for, without the use of conventional hybridoma technology. In this work, phage display technology was used to construct, select and characterize a combinatorial single chain fragment variable (scFv) antibody library against bovine herpesvirus type 1 (BoHV-1) from the immune repertoire of chickens immunized with the virus. In silico analysis of the hypervariable domains of the antibody heavy chains revealed a high frequency of scFv fragments with low variability, suggesting that selection had probably been carried out and favored by a few immunogenic viral antigens. The reactivity of the scFv fragments selected against BoHV-1 was demonstrated by Phage-ELISA. A significant increase in antibody reactivity to the target was observed after six rounds of library selection, showing its potential use as a molecule for BoHV-1 diagnosis. The strategy described here opens up a field for the use of phage display as a tool for selection of monoclonal antibodies that could be used for theranostic applications against infectious and parasitic diseases of veterinary interest. Key words: Antibody engineering. BoHV-1. Diagnosis. ScFv library.
ResumoA especificidade dos anticorpos monoclonais (mAb) aos alvos desejados torna estas moléculas adequadas para uso em diagnóstico ou terapia de uma vasta gama de agentes patogênicos. Biblioteca de anticorpos apresentados em fagos filamentosos é uma metodologia para a produção de mAbs, podendo ser utilizada como alternativa à tecnologia de hibridoma convencional, tradicionalmente empregada para este fim. Neste trabalho, a tecnologia de Phage display foi usada para construir, selecionar e caracterizar uma biblioteca combinatorial de fragmentos de anticorpos de cadeia única (scFv) contra o Herpesvírus bovino tipo 1 (BoHV-1) a partir do repertório imune de galinhas imunizadas com o vírus. A análise in silico dos
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