Plasma defensin concentrations are elevated in patients with septicemia or bacterial meningitis.

We measured concentrations of defensins (human neutrophil peptides) in the plasma of healthy volunteers and patients with sepsis and meningitis. When a sensitive enzyme immunoassay was used, defensins were detected in plasma samples from 13 of 24 healthy blood donors, with a mean +/- SD of 42 +/- 53 ng/ml. Defensin levels in plasma samples from seven patients with sepsis at the onset of disease ranged from 900 ng/ml to 170,000 ng/ml. In 10 patients with meningitis in the initial phase of disease, plasma defensin concentrations ranged from 120 ng/ml to 910 ng/ml. Defensin concentrations in the plasma of both patient groups were significantly higher than those in healthy blood donors (p << 0.01), and patients with sepsis had higher defensin levels than patients with meningitis (p < 0.01). Defensin levels were significantly (p < 0.01) lower after the beginning of specific antibiotic therapy. Defensin concentrations in the plasma of patients with sepsis and meningitis correlated only weakly (r = 0.38) with blood neutrophil count. In vitro studies of defensin added to plasma indicated that all defensin was bound to plasma proteins. At high concentrations (1000 micrograms/ml), defensins caused precipitation of plasma proteins. Because plasma defensin levels may reflect neutrophil activation at sites of infection and inflammation, studies of the clinical utility of defensin ELISA are indicated.

The effect of biotinylation on the antigenic specificity of anti-defensin monoclonal antibodies.

We studied the effects of biotinylation on three monoclonal antibodies (Mabs) that were raised against carrier protein conjugates of human defensin HNP-1, and of rabbit defensins NP-2 and NP-5 respectively. Before biotinylation, each Mab specifically bound to its peptide hapten. Biotinylation of these Mabs by the N-hydroxysuccinimide-biotin (NHS-biotin) resulted in crossreactivity of each Mab with the two irrelevant defensin peptides. In contrast, Mab specificity was preserved after biotinylation with biotin hydrazide, which links biotin to the glycan moiety of antibodies. The effects of NHS-biotinylation were in part mimicked by 2,4-dinitrofluorobenzene, another agent that modified primary amine groups of proteins, suggesting that this modification contributed to the change in antibody specificity. When a high degree of antigenic specificity against peptide immunogens is required, biotinylation on the glycan moiety of Mabs may be preferable.