Lactoferrin modifies the effects of endotoxin in alveolar macrophages

Lactoferrin (LF) deficiency in bronchial fluid is a risk factor for developing broncho-pulmonary dysplasia (BPD). Recently, an endotoxin (LPS)-binding region was described on LF. Since lung infection also increases the risk of BPD, the responses of bronchoalveofar macrophages (M φ) to LPS ± LF were studied. A rat M φ cell line (5 × 10⁵ cells/ml) was stimulated for 24 h with LPS (100 ng/ml) ± 500 μg/ml of human recombinant LF (rh-LF). NO production was measured as NO₂^- (Griess reaction) in culture supernatants, and the μM NO₂^- content was: no LPS = 3.4±0.5*, LPS = 20.2±1.4^†, rh-LF = 17.2±2.0^†, and LPS + rh-LF = 25.5±1.9^† (* mean ± SEM, n = 3 expts. done in duplicate, † = P<0.001 v. no LPS). At 24 hours, Northern analyses for inducible NO synthase (rat cDNA probe) were performed, and a representative blot showing M φ expression is shown below. iNOS mRNA → CONDITIONS: No LPS LPS LPS + rh-LF rh-LF iNOS/Actin ratio: 0.05 1.12 0.63 0.46. Nuclear factor kappa B activation (mobility shift assay) was the same at 2 h for LPS and LPS + LF, but was reduced for LF exposure alone. Early growth response-1 gene induction, an early marker of M φ activation, was also reduced at 2 h after LF and LPS + LF treatment compared to LPS alone. We conclude that LF can activate M φ and can modify M φ responses to LPS. These findings are likely of importance in controlling lung inflammation.