Engagement of Toll-like receptors by mycoplasmal superantigen: downregulation of TLR2 by MAM/TLR4 interaction

Abstract

SummaryMycoplasma arthritidis mitogen (MAM) is a superantigen (SAg) from M. arthritidis , an agent of murine toxic shock syndrome and arthritis. We previously demonstrated that C3H/HeJ and C3H/HeSnJ mice that differ in expression of TLR4 differed in immune reactivity to MAM. We show here that MAM directly interacts with TLR2 and TLR4 by using monoclonal antibodies to TLR2 and TLR4 which inhibit cytokine responses of THP-1 cells to MAM. Also, using macrophages from C3H substrains and TLR2-deficient mice, we confirmed that both TLR2 and TLR4 are used by MAM. Levels of IL-6 in supernatants of MAM-challenged macrophages were higher in mice which expressed only TLR2, lesser with both TLR2 and TLR4, and absent in mice lacking both TLR2 and TLR4. In addition, expression of TLR2 and TLR4 was moderately upregulated in wild-type cells but cells lacking TLR4 showed a fivefold increase in TLR2 expression. Further, blockade of TLR4 on macrophages of C3H/ HeN mice with antibody greatly increased expression of TLR2 and release of IL-12p40 in response to MAM. These results indicate that the SAg, MAM, interacts with both TLR2 and TLR4 and that TLR4 signalling might downregulate the MAM/TLR2 inflammatory response.

A Microbial TLR2 Agonist Imparts Macrophage-Activating Ability to Apolipoprotein A-1

“…Splenocytes, RAW 264.7 cells, and murine adherent peritoneal cells were cultured in RPMI 1640 medium, as described previously (4). Macrophage suspensions were prepared from pools of three to five mice.…”

“…It has now been established that diverse TLRs not only control the innate immune response recognizing a wide variety of exogenous and endogenous agonists (9,12), but may also control the subsequent direction of the adaptive immune response (4,(13)(14)(15). These interactions may be beneficial to the host by promoting a rapid immune response to invading organisms or may trigger an acute inflammatory reaction as seen in toxic shock syndromes (4).…”

“…In view of our findings on multiple TLR usage by several agonists present in the arthritogenic and toxigenic M. arthritidis species (4,6), the present work was initiated to more fully characterize these moieties. In this study, we purify and characterize the 28-kDa bioactive component described previously (6) and show, unexpectedly, that it is an apolipoprotein A-1 (apoA-1)-like molecule that acquires bioactivity by associating with mycoplasma cells.…”

“…It has now been established that diverse TLRs not only control the innate immune response recognizing a wide variety of exogenous and endogenous agonists (9,12), but may also control the subsequent direction of the adaptive immune response (4,(13)(14)(15). These interactions may be beneficial to the host by promoting a rapid immune response to invading organisms or may trigger an acute inflammatory reaction as seen in toxic shock syndromes (4). TLR/endogenous interactions may also lead to autoimmunity (16,17), and chronic infections may promote asthma (18); in addition, there is increasing evidence that agonists from multiple microbial agents may be a contributing factor to the development of atherosclerosis (19,20).…”

“…Mycoplasma arthritidis is a natural pathogen of rodents, which causes acute and chronic arthritis, lethal toxic shock, and a necrotizing fasciitis-like syndrome in genetically predisposed mice and rats (3). Virulence factors include a potent superantigen (SAg), M. arthritidis mitogen (MAM) (3), which uses TLR2 and TLR4 (4). It also possesses two distinct adhesins and a bacteriophage, all of which are thought to contribute to disease (5).…”