Expression of a recombinant Fab antibody fragment against cruzipain, the major cysteine proteinase of Trypanosoma cruzi

Cruzipain, the major proteinase of Trypanosoma cruzi, plays an important role in the biology of this parasite. This study reports the development of a recombinant Fab antibody, using RNA isolated from the anti-Ag136B6 hybridoma against cruzipain. This procedure involves the use of cDNAs obtained with the aid of a specific set of primers complementary to the complete light kappa chain (LK) and the first two do mains of the IgG1 heavy chain (VH/CH1). These products were subsequently cloned in the pComb3 system, from which the gIII gene had been removed, and expressed in Escherichia coli cells. The recombinant Fab molecule recognized cruzipain by ELISA, in a fashion similar to the original mAb anti-Ag163B6. Nucleotide sequence analysis of the recombinant molecule, together with its immunological recognition by specific anti-mouse IgG (Fab)a, indicated the immunoglobulin nature of the recombinant product. Moreover, both the mAb anti-Ag136B6 and the soluble Fab fragment described here react similarly with the intact parasite surface, as observed in an indirect immunofluorescence assay. In conclusion, our recombinant Fab anti-Ag 163B6 allows the possible use of this molecule for diagnosis, antigen purification, and eventually treatment of Chagas-afflicted individuals. (C) 1998 Academic Press.