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

We previously observed that Ureaplasma urealyticum respiratory tract coloni zation in infants with a birth weight of less than or equal to1,250 g was a ssociated 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, Vis cardi, Pediatr. Infect, Dis, J, 17:321-328, 1998), We hypothesized that U. urealyticum alters the host immune response in the presence of a coinflamma tory stimulus (e.g,, bacterial infection or hyperoxia) by shifting the bala nce of cytokine expression towards the proinflammatory cytokines, To test t his 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 lipopolysacch aride [LPS])-stimulated human monocytes from adult peripheral blood and fro m term and preterm cord blood, U, urealyticum alone and in combination with LPS induced concentration- and development-dependent changes in cytokine r elease. In vitro inoculation with low-inoculum U. urenlyticum (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, (i i) stimulated TNF-alpha and IL-8 release by preterm cells, and (iii) augmen ted LPS-stimulated TNF-at release in all cells. In preterm cells, high-inoc ulum 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 si gnificantly affect LPS-induced cytokine release in adult cells. We speculat e that U. urealyticum enhances the proinflammatory response to a second inf ection by blocking expression of counterregulatory cytokines (IL-6 and IL-1 0), predisposing the preterm infant to prolonged and dysregulated inflammat ion, lung injury, and impaired clearance of secondary infections.