Small, antibacterial and large, inactive peptides of neutrophil granules share immunoreactivity to a monoclonal antibody.

Monoclonal antibodies were raised against a bactericidal protein fraction that was purified from an extract of bovine neutrophil granules and that was previously shown (A. Savoini, R. Marzari, L. Dolzani, D. Serranò, G. Graziosi, R. Gennaro, and D. Romeo, Antimicrob. Agents Chemother. 26:405-407, 1984) to inhibit bacterial DNA synthesis. One of these antibodies, BP97, was covalently linked to Affi-Gel 10 and was used for immunoaffinity chromatography of granule extracts. Elution of the bound proteins, followed by reversed-phase high-performance liquid chromatography, generated several peptides whose molecular weights fell in the range of 1,600 to 64,000 and which reacted to BP97 but not to other mouse monoclonal or polyclonal antibodies. The reaction to BP97 appeared to be specific, inasmuch as a full panel of cationic oligo- or polypeptides was not recognized by this monoclonal antibody. Among the purified granule polypeptides, the more cationic ones (with molecular weights of 4,300 to 8,000) inhibited the growth of Escherichia coli at a MIC of 12 to 50 micrograms/ml. In addition, a 1,600-molecular-weight, highly cationic peptide also inhibited the growth of Staphylococcus aureus and Staphylococcus epidermidis at MICs of 3 to 8 micrograms/ml.