MAPK9 and immune system toxicity: In vitro immunotoxicity was observed in RAW 264.7 murine leukemic monocyte macrophages exposed to TiO2 NPs by simultaneous induction of immunocyte apoptosis and multiple toll-like receptors (TLRs) signaling through oxidative stress-dependent SAPK/JNK (Stress-activated protein kinases (SAPK)/Jun amino-terminal kinases (JNK)) and p38 mitogen-associated protein kinase activation [28].