Interleukin-6 production from Theiler’s virus-infected macrophages in mice

Objective: Chronic viral infections can lead to inflammatory disease.  Macrophages from SJL/J mice exposed to Theiler’s Murine Encephalomyelitis Virus (TMEV) become chronically infected while those of B10.S mice do not. As a result, SJL/J mice with chronic TMEV-infected macrophages develop a neuroinflammatory disease, similar to Multiple Sclerosis, despite more Interferon-beta (IFNb) and less IL-12 expression, while B10.S mice do not.  Excessive macrophage Interleukin-6 (IL-6) expression from TMEV-infected SJL/J macrophages due to MAP-kinase activation in TLR-pathways is hypothesized to contribute significantly to disease.

Method: In order to test this hypothesis, macrophages from SJL/J and B10.S mice were challenged with TMEV or TLR3 and TLR4 agonists (polyIC and LPS, respectively) and IL-6 expression was evaluated by qRT-PCR and ELISA.  To determine the role of ERK and p38 MAP-kinase signaling pathways in IL-6 expression and TMEV replication, macrophages were pretreated with the p38 MAPK inhibitor, SB203580, or the ERK-MAPK inhibitor, U0126, before challenged with TMEV.  To determine if pretreatment with IFNb or IL-12 could influence TMEV induced IL-6 expression, SJL/J and B10.S macrophages were pretreated with recombinant IFNb, IL-12p70, or IL-12p40.

Result: The results show that macrophages stimulated with TMEV, polyIC, or LPS express IL-6 but SJL/J macrophages produce significantly more IL-6 mRNA and significantly less IL-6 protein than B10.S macrophages. In contrast to SB203580, U0126 significantly lowered TMEV-induced IL-6 expression but significantly increased TMEV replication in macrophages. IL-12 dramatically, and to a lesser extent IFNb, augmented IL-6 expression from TMEV-infected macrophages of both mouse strains. 

Conclusion: Therefore, murine macrophages express high levels of IL-6 in response to TMEV in a TLR/ERK-MAP-kinase dependent manner.  However, SJL/J macrophages produce less IL-6 in response to TMEV infection than B10.S, which may be related to decreased IL-12 from TMEV-infected SJL/J macrophages compared with B10.S macrophages. The data suggest that IL-6 and ERK-MAP-kinases have an unknown role in innate anti-viral immunity.