Ureaplasma urealyticum modulates endotoxin-induced cytokine release by human monocytes derived from preterm and term newborns and adults

Abstract

We previously observed that Ureaplasma urealyticum respiratory tract colonization in infants with a birth weight of < or =1,250 g was associated with increases in the tracheal aspirate proinflammatory cytokines tumor necrosis factor alpha (TNF-alpha) and interleukin-8 (IL-8) relative to the counterregulatory cytokine IL-6 during the first week of life (A. M. Patterson, V. Taciak, J. Lovchik, R. E. Fox, A. B. Campbell, and R. M. Viscardi, Pediatr. Infect. Dis. J. 17:321-328, 1998). We hypothesized that U. urealyticum alters the host immune response in the presence of a coinflammatory stimulus (e.g., bacterial infection or hyperoxia) by shifting the balance of cytokine expression towards the proinflammatory cytokines. To test this hypothesis, we compared the release of TNF-alpha, IL-8, IL-6, and IL-10 in vitro by unstimulated and U. urealyticum (with or without lipopolysaccharide [LPS])-stimulated human monocytes from adult peripheral blood and from term and preterm cord blood. U. urealyticum alone and in combination with LPS induced concentration- and development-dependent changes in cytokine release. In vitro inoculation with low-inoculum U. urealyticum (10(3) color-changing units [CCU]) (i) partially blocked the LPS-stimulated IL-6 release by all cells and reduced LPS-stimulated IL-10 release by preterm cells, (ii) stimulated TNF-alpha and IL-8 release by preterm cells, and (iii) augmented LPS-stimulated TNF-alpha release in all cells. In preterm cells, high-inoculum U. urealyticum (10(6) CCU) (i) stimulated TNF-alpha and IL-8, but not IL-6 or IL-10, release and (ii) augmented LPS-stimulated TNF-alpha and IL-8 release. High-inoculum U. urealyticum (i) stimulated release of all four cytokines in term cells and IL-8 release in adult cells and (ii) augmented LPS-induced TNF-alpha, IL-10, and IL-8 release in term cells but did not significantly affect LPS-induced cytokine release in adult cells. We speculate that U. urealyticum enhances the proinflammatory response to a second infection by blocking expression of counterregulatory cytokines (IL-6 and IL-10), predisposing the preterm infant to prolonged and dysregulated inflammation, lung injury, and impaired clearance of secondary infections.

FIG. 1

Dose-dependent effects of in vitro infection with U. urealyticum on preterm monocyte cytokine release. Monocytes from preterm cord blood (24 to 32 weeks) were incubated with CRPMI–10% FCS alone, U. urealyticum at 10³ CCU (UU3) (low inoculum) or 10⁶ CCU (UU6) (high inoculum), or LPS (100 ng/ml) with or without U. urealyticum for 24 h. (A) TNF-α; (B) IL-6; (C) IL-10; (D) IL-8. Results are expressed as percentages of the LPS positive control value (mean ± SEM; n = 6). ∗, P < 0.05 versus medium control; †, P < 0.05 versus LPS.

FIG. 2

Dose-dependent effects of in vitro infection with U. urealyticum on term monocyte cytokine release. Monocytes from term cord blood were incubated with CRPMI–10% FCS alone, U. urealyticum at 10³ CCU (UU3) to 10⁶ CCU (UU6), or LPS (100 ng/ml) with or without U. urealyticum for 24 h. (A) TNF-α; (B) IL-6; (C) IL-10; (D) IL-8. Results are expressed as percentages of the LPS positive control value (mean ± SEM; n = 4). ∗, P < 0.05 versus medium control; †, P < 0.05 versus LPS.

FIG. 3

Dose-dependent effects of in vitro infection with U. urealyticum on adult monocyte cytokine release. Monocytes from adult blood were incubated with CRPMI–10% FCS alone, U. urealyticum at 10³ CCU (UU3) to 10⁶ CCU (UU6), or LPS (100 ng/ml) with or without U. urealyticum for 24 h. (A) TNF-α; (B) IL-6; (C) IL-10; (D) IL-8. Results are expressed as percentages of the LPS positive control value (mean ± SEM; n = 6). ∗, P < 0.05 versus medium control; †, P < 0.05 versus LPS.

FIG. 4

Comparison of cytokine release by preterm, term, and adult monocytes infected in vitro with low-inoculum U. urealyticum. Monocytes from preterm and term cord blood and adult peripheral blood were incubated with CRPMI–10% FCS medium alone, U. urealyticum (UU) at 10³ CCU (low inoculum), or LPS (100 ng/ml) with or without U. urealyticum for 24 h. (A) TNF-α; (B) IL-6; (C) IL-10; (D) IL-8. Results are expressed as percentages of the LPS positive control value (mean ± SEM; preterm n = 8, term n = 12, and adult n = 6). ∗, P < 0.05 versus LPS.

FIG. 5

Time course of effects of LPS and U. urealyticum alone and in combination on preterm (30 weeks) monocyte cytokine release. Preterm monocytes were incubated with medium, U. urealyticum (UU) at 10³ CCU, or LPS with or without U. urealyticum for 2 to 24 h. (A) TNF-α; (B) IL-6; (C) IL-10. Results are from a representative experiment of three experiments.