Differential production of proinflammatory cytokines: in vitro PRRSV and Mycoplasma hyopneumoniae co-infection model

An in vitro culture system was developed to investigate the induction of pr oinflammatory cytokines by Mycoplasma hyopneumoniae and porcine reproductiv e and respiratory syndrome virus (PRRSV). M. hyopneumoniae infected porcine tracheal ring explants were co-cultured with PRRSV infected pulmonary alve olar macrophages (PAMs) for 24 h to assess the cytokine production of each pathogen alone and the interaction between the two pathogens in vitro. Semi quantitative RT-PCR was used to measure interleukin (IL) 1 alpha, IL1 beta, IL6, IL8, IL10, IL12 and tumor necrosis factor (TNF) alpha mRNA in PAMs. C ommercial ELISAs were used to measure soluble IL1 beta, IL8, IL10 and TNF i n the culture supernatant. In the dual infected group, mRNA expression of I L1 alpha, IL1 beta, IL8 and TNF was increased. Both the M. hyopneumoniae- a nd PRRSV-infected only groups tended to have increased expression of IL1 al pha, IL1 beta and IL8 mRNA, although no statistical difference was observed . Increased levels of IL1 beta, IL8 and IL10 were present in the supernatan t of the dual infected group as measured by ELISA. No increase in soluble T NF was observed in any of the groups. IL8 levels appeared high in all group s independent of infection status. The cause of the elevated IL8 was unknow n, however, it may have been a non-specific response by the cells to tissue damage during the harvesting of the tracheal rings. Correlation between mR NA expression and the soluble cytokine levels were similar in the dual infe cted groups with the exception of IL10 and TNF Levels of mRNA and soluble p rotein levels in the single pathogen infected groups were not as consistent . The increased production of proinflammatory cytokines IL1 alpha, IL1 beta , IL8 and TNF in the group infected with both M. hyopneumoniae and PRRSV su ggests that cytokine induced inflammation may play an important role in the severe, chronic pneumonia induced by the concurrent infection of the two p athogens. (C) 2001 Elsevier Science B.V. All rights reserved.