NPPB and heart failure: In this study we aim to investigate the effects of host strain, culture medium and aeration conditions on the production and extracellular leakage of Fab fragments in shaken E. coli cultures by the example of Fabs binding specifically to N-terminal pro-brain natriuretic peptide (NTproBNP), an important diagnostic marker of heart failure that can be detected from serum by an immunoassay applying the anti-NTproBNP Fabs [19].