Staphylococcus aureus enterotoxins induce IL-8 secretion by human nasal epithelial cells

Abstract

Background: Staphylococcus aureus produces a set of proteins which act both as superantigens and toxins. Although their mode of action as superantigens is well understood, little is known about their effects on airway epithelial cells.

Methods: To investigate this problem, primary nasal epithelial cells derived from normal and asthmatic subjects were stimulated with staphylococcal enterotoxin A and B (SEA and SEB) and secreted (supernatants) and cell-associated (cell lysates) IL-8, TNF-alpha, RANTES and eotaxin were determined by specific ELISAs.

Results: Non-toxic concentrations of SEA and SEB (0.01 microg/ml and 1.0 microg/ml) induced IL-8 secretion after 24 h of culture. Pre-treatment of the cells with IFN-gamma (50 IU/ml) resulted in a further increase of IL-8 secretion. In cells from healthy donors pretreated with IFN-gamma, SEA at 1.0 mug/ml induced release of 1009 pg/ml IL-8 (733.0-1216 pg/ml, median (range)) while in cells from asthmatic donors the same treatment induced significantly higher IL-8 secretion - 1550 pg/ml (1168.0-2000.0 pg/ml p = 0.04). Normal cells pre-treated with IFN-gamma and then cultured with SEB at 1.0 mug/ml released 904.6 pg/ml IL-8 (666.5-1169.0 pg/ml). Cells from asthmatics treated in the same way produced significantly higher amounts of IL-8--1665.0 pg/ml (1168.0-2000.0 pg/ml, p = 0.01). Blocking antibodies to MHC class II molecules added to cultures stimulated with SEA and SEB, reduced IL-8 secretion by about 40% in IFN-gamma unstimulated cultures and 75% in IFN-gamma stimulated cultures. No secretion of TNF-alpha, RANTES and eotaxin was noted.

Conclusion: Staphylococcal enterotoxins may have a role in the pathogenesis of asthma.

Figure 1

Release of interleukin-8 (IL-8) in cell culture supernatants after interferon-gamma (IFN-γ) pretreatment. Data are shown as individual points, the line represents the median. Black symbols = no IFN-γ pretreatment, open symbols = IFN-γ pretreatment. P values reaching statistical significance are marked on the graph. * = P < 0.05; ** = P < 0.01.

Figure 2

Interleukin-8 (IL-8) release from cells derived from normal subjects in response to SEA after 6 and 24 hour stimulation. Data are shown as individual points, the line represents the median. ■ = control (unstimulated cells), ▲ = 0.01 μg/ml SEA, ● = 1 μg/ml SEA. Median values of IL-8 release at 6 hours: control P values reaching statistical significance are indicated on the graph.

Figure 3

Interleukin-8 (IL-8) from cells derived from asthmatic subjects in response to SEA after 6 and 24 hour stimulation. Data are shown as individual points, the line represents the median. ■ = control (unstimulated cells), ▲ = 0.01 μg/ml SEA, ● = 1 μg/ml SEA. P values reaching statistical significance are indicated on the graph.

Figure 4

Interleukin-8 (IL-8) release from interferon-gamma (IFN-γ)-treated cells derived from normal subjects in response to SEA after 6 and 24 hour stimulation. Data are shown as individual points, the line represents the median. ■ = control (unstimulated cells), ▲ = 0.01 μg/ml SEA, ● = 1 μg/ml SEA. P values reaching statistical significance are indicated on the graph.

Figure 5

Interleukin-8 (IL-8) release from interferon-gamma (IFN-γ)-treated cells derived from asthmatic subjects in response to SEA after 6 and 24 hour stimulation. Data are shown as individual points, the line represents the median. ■ = control (unstimulated cells), ▲ = 0.01 μg/ml SEA, ● = 1 μg/ml SEA. P values reaching statistical significance are indicated on the graph.

Figure 6

Interleukin-8 (IL-8) release from cells derived from normal subjects in response to SEB after 6 and 24 hour stimulation. Data are shown as individual points, the line represents the median. ■ = control (unstimulated cells), ▲ = 0.01 μg/ml SEB, ● = 1 μg/ml SEB. P values reaching statistical significance are indicated on the graph.

Figure 7

Interleukin-8 (IL-8) release from cells derived from asthmatic subjects in response to SEB after 6 and 24 hour stimulation. Data are shown as individual points, the line represents the median. ■ = control (unstimulated cells), ▲ = 0.01 μg/ml SEB, ● = 1 μg/ml SEB. P values reaching statistical significance are indicated on the graph.

Figure 8

Interleukin-8 (IL-8) releases from interferon-gamma (IFN-γ)-treated cells derived from normal subjects in response to SEB after 6 and 24 hour stimulation. Data are shown as individual points, the line represents the median. ■ = control (unstimulated cells), ▲ = 0.01 μg/ml SEB, ● = 1 μg/ml SEB. P values reaching statistical significance are indicated on the graph.

Figure 9

Interleukin-8 (IL-8) release from interferon-gamma (IFN-γ)-treated cells derived from asthmatic subjects in response to SEB after 6 and 24 hours stimulation. Data are shown as individual points, the line represents the median. ■ = control (unstimulated cells), ▲ = 0.01 μg/ml SEB, ● = 1 μg/ml SEB. P values reaching statistical significance are indicated on the graph.