Dynamic changes in neutrophil defensins during endotoxemia

Abstract

Bacterial endotoxin or lipopolysaccharide (LPS) is an important causative agent of sepsis. This study determines the expression of defensins NP-2 and NP-5 and the function of polymorphonuclear leukocytes (PMN) in rabbits treated with LPS. PMN functional activity was assessed by measuring CD18 expression and H(2)O(2) production and by examining the lungs. NP-2 and, to a minor extent, NP-5 of circulating PMN increase during endotoxemia. This early increase is concomitant with neutrophilia and elevated CD18 expression and H(2)O(2) production, as well as with enhanced NP-2 immunoreactivity in pulmonary microvessels. A decline in defensins, shortly after the last LPS treatment, is associated with a decrease in the circulating activated PMN and enhanced immunoreactivity in the inflammatory cells, as well as with lung tissue damage. This study shows that LPS-induced changes in the defensins of circulating PMN correlate with the number and activated condition of these cells and suggests that PMN-derived products implement the inflammatory reaction that leads to lung injury and sepsis.

FIG. 1

(A and B) Kinetics of NP-2 and NP-5 in circulating PMN. NP-2 increases by 24 to 48 h (P < 0.05) (A), and NP-5 rises at 48 h (P = 0.19) (B). Both of these peptides fall at 97 h. Values show means ± standard errors of the means. P < 0.05 from the baseline (∗).

FIG. 2

(A and B) CD18 expression and H₂O₂ production in circulating PMN. CD18 expression (A) and H₂O₂ production (B) increase with repeated doses of LPS and exhibit a peak at 48 h. These parameters fall at 97 h and do not change with saline treatment. Values represent means ± standard errors of the means. P < 0.05 from the baseline (∗) or from 96 h (∗∗).

FIG. 3

(A to F) NP-2 (MCP-2) immunoreactivity. PMN-containing defensins are scarce in the lungs of control rabbits (arrows) (A) and accumulate in the capillaries of animals treated with LPS for 49 h (arrows) (B). Defensin-rich phagocytes are prominent in the interstitial (arrows) (C) and alveolar (D) spaces and are less evident in the capillaries of animals treated with LPS for 97 h (E). (F) IgG1-negative control. Magnifications are as follows: ×200 (A, B, E, and F), ×700 (C), and ×850 (D).

FIG. 4

(A to D) Changes in the lungs of rabbits treated with LPS for 49 h (A) and 97 h (B to D). Note PMN adhered to the endothelium (A), endothelial cell vacuolization (B), interstitial cell infiltrates (C), and alveolar epithelial cell damage with fibrillar deposits (D). Magnifications are as follows: ×7,700 (A), ×2,150 (B), ×2,750 (C), and ×10,000 (D).