LTB4 increases nasal neutrophil activity and conditions neutrophils to exert antiviral effects

Abstract

Background: Leukotriene B4 (LTB4) recruits and activates neutrophils. Accordingly, this leukotriene is involved in innate defense actions.

Objective: To examine if nasal LTB4 can produce neutrophil activity and to explore whether or not LTB4 can condition neutrophils to exert virucidal effects in vitro and in vivo.

Methods: 1. Twenty-three healthy subjects received nasal LTB4 in a randomized and sham-controlled design. Symptoms were scored and nasal lavages carried out. Myeloperoxidase (MPO) and α-defensins were monitored as indices of neutrophil activity. IL-8, eosinophil cationic protein (ECP) and α(2)-macroglobulin were measured as indices of pro-inflammatory cytokine production, eosinophil activity, and plasma exudation. 2. Supernatants from neutrophils activated by LTB4 in vitro were assayed for virucidal activity against respiratory viruses. 3. In 38 healthy individuals, nasal inoculation with human rhinovirus-16 (HRV-16) was performed. In a preliminary study, intervention with LTB4 was given in a randomized and controlled design. Symptoms, virus replication, and antibody-titres were monitored.

Results: 1. LTB4 produced statistically significant increases in MPO and α-defensins, whereas IL-8, ECP, and α(2)-macroglobulin were unaffected. 2. The supernatants efficiently killed human coronavirus, respiratory syncytial virus, and influenza B virus. 3. HRV-16 replication was lower in subjects receiving LTB4, but this difference failed to reach statistical significance. Common cold symptoms and incidence of seroconversion were unaffected.

Conclusion: Nasal LTB4 induces a selective recruitment/activation of neutrophils. LTB4 can condition neutrophils to exert virucidal effects in vitro and may reduce virus replication in vivo. We suggest that the condition induced by LTB4 reflects an enhanced state of innate defense.

Figure 1

LTB4 produces increased nasal lavage levels of MPO and α-defensins; Levels of MPO (A) and α-defensins (B) in nasal lavages obtained prior to challenge with sham and two doses of LTB4 as well as 1 and 4 h thereafter. LTB4 increased levels of MPO and α-defensins: these changes reached statistical significance for MPO at 1 as well as 4 h post challenge for both doses and for α-defensins at 1 h post challenge for LTB4 (2.0 μg). Comparisons were made with sham challenge at each time-point. Note that the repeated lavages produced gradually lower levels of MPO following sham challenge (as for IL-8, ECP, and α₂-macroglobulin: Table 4), whereas the sham challenge increased the levels of α-defensins. Data are expressed as median ± IQR (n = 23). ∗ Denotes p < 0.05 and ∗∗ p < 0.01, paired comparisons.

Figure 2

LTB4 conditions neutrophils to exert antiviral effects; Supernatants from neutrophils conditioned with LTB4 produced virucidal effects against human coronavirus (A), RSV (B), and influenza B virus (C). Control experiments indicated that the effect was specific for the interaction between LTB4 and neutrophils. Data are expressed as mean TCID₅₀ + S.D. from one experiment representative of at least two independent experiments. ∗ Denotes p < 0.05.

Figure 3

The control subjects presented viral replication and common cold symptoms; Data from control subjects inoculated with HRV-16. These subjects presented HRV-16 replication (peaking three days following inoculation), as indicated by qPCR (A), and mild nasal symptoms of the common cold (B). Data are expressed as mean ± SEM (n = 20). ∗ Denotes p < 0.05 and ∗∗ denotes p < 0.01, paired comparisons with baseline levels prior to inoculation.

Figure 4

Comparison of viral replication and common cold symptoms between the two groups; Virus replication (A) and nasal symptoms (B) from the LTB4 and control groups. Virus replication was lower in the LTB4-group, but this difference (c.f. control group) failed to reach statistical significance overall as well as at all time-points. Nasal symptoms of the common cold were mild an unaffected by LTB4. Data are expressed as mean ± SEM (n = 20: control and 18: LTB4).