Asian sand dust (ASD), a type of particulate matter (PM) found in Asia, can be transported to East Asia. We recently found that acute splenic inflammation is induced by ASD in mouse models. In this study, we examined the effect of sub-chronic ASD exposure on mouse immune cells. Mice were intratracheally administered ASD once every 2 weeks for 8 weeks and killed 24 hours after the final administration. Wild-type (WT) mice showed increased cell viability after ASD administration. In contrast, ASD administration induced splenocyte activation in toll-like receptor (TLR)2(-/-), but not TLR4(-/-) mice. Furthermore, concanavalin A-induced interleukin-2 production increased after ASD administration in WT and TLR2(-/-) mice, but not in TLR4(-/-) or myeloid differentiation factor (MyD)88(-/-) mice. Immunoblotting demonstrated that nuclear factor kappa B (NF-kappa B) was activated in WT mice, but not in TLR4(-/-) or MyD88(-/-) mice. The NF-kappa B-dependent gene products CDK2 and intercellular cell adhesion molecule-1 were upregulated upon ASD administration in WT mice, but not in TLR4(-/-) or MyD88(-/-) mice. Furthermore, the particles themselves, rather than particle constituents, activated NF-kappa B in CD4-positive cells through the TLR4 or MyD88 pathway. Taken together, these results indicate that particle-induced splenic inflammation occurs via TLR4-MyD88 signaling.