Toxoplasma gondii-derived heat shock protein 70 induces lethal anaphylactic reaction through activation of cytosolic phospholipase A2 and platelet-activating factor via Toll-like receptor 4/myeloid differentiation factor 88

ABSTRACT Toxoplasma gondii‐derived heat shock protein 70 (T.g.HSP70) was proven to induce IFN‐γ‐dependent lethal anaphylactic reaction in T. gondii‐infected mice through an alternative PAF‐mediated pathway, but not the classical immunoglobulin (Ig)E‐dependent pathway. Although marked IFN‐γ production was observed by CD11b+, CD11c+, CD4+ and CD8+ splenocytes, CD11b+ and CD11c+ cells were shown to be the key effecter cells which generated pro‐inflammatory lipid such as PAF and caused T.g.HSP70‐induced anaphylactic reaction. In the present study, we found that the T.g.HSP70‐induced anaphylactic reaction was not observed in TLR 4‐deficient (−/−) mice, whereas it was observed in WT and TLR2−/− mice. The mRNA expression of PAF‐AH, the main enzyme for PAF degradation, increased in T. gondii‐infected WT and TLR2−/− but not in TLR4−/− mice after T.g.HSP70 injection. Furthermore, phosphorylation of cPLA2, which is the key enzyme for pro‐inflammatory lipid generation, was detected in CD11b+ splenocytes of WT and TLR2−/− mice but not in TLR4−/− mice. Subsequently, cPLA2 activation was suppressed by inhibiting the TLR4‐directed p38 and p44/42 MAPK pathways. However, T.g.HSP70‐induced anaphylactic reaction was observed in TRIF−/− mice, but not in MyD88−/− mice. These findings indicate the cPLA2 activated‐PAF production via TLR4/MyD88‐dependent, but not TRIF‐dependent, signaling pathway in T.g.HSP70‐induced anaphylactic reaction in T. gondii‐infected mice.