Expression and distribution of Toll-like receptors in the brain during murine neurocysticercosis

The functions of Toll-like receptors (TLRs) 11–13 in central nervous system (CNS) infections are currently unknown. Using a murine model of neurocysticercosis, we investigated the expression and distribution of TLRs 11–13 by using both gene specific real-time PCR analysis and in situ immunofluoresence microscopy in both control and neurocysticercosis brains. In the mock infected brain, mRNAs of TLRs 11–13 were constitutively expressed. Parasite infection caused an increase of both mRNAs and protein levels of all three TLRs by several fold. All three TLR proteins were present in both CNS and immune cell types. Among them TLR13 was expressed the most in terms of number of positive cells and brain areas expressing it, followed by TLR11 and TLR12 respectively. Among the nervous tissue cells, TLRs 11–13 protein levels appeared highest in neurons. However, TLR13 expression was also present in ependymal cells, endothelial cells of pial blood vessels, and astrocytes. In contrast, infiltrating CD11b and CD11c positive myeloid cells predominantly produced TLR11 protein, particularly early during infection at 1 wk post infection (~50% cells). TLRs 12 and 13 proteins were present on approximately 5% of infiltrating immune cells. The infiltrating cells positive for TLRs 11–13 were mostly of myeloid origin, CD11b+ cells. This report provides a comprehensive analysis of the expression of TLRs 11–13 in normal and parasite infected mouse brains and suggests a role for them in CNS infections.