Abstract
Toxoplasma gondii (T. gondii) is an obligate intracellular protozoan that can infect almost all nucleated cells. Histone proteins and DNA form the nucleosomes, which are the fundamental building blocks of eukaryotic chromatin. Histone 4 is an essential component of a histone octamer. In the present study, T. gondii histone 4 (TgH4) was cloned and the regulatory effect of TgH4 on murine macrophages was characterized. Bioinformatics analysis revealed that TgH4 was highly conserved in structure. Recombinant TgH4 (rTgH4) protein was identified by sera from rats experimentally infected with T. gondii and native TgH4 in the total soluble protein of T. gondii tachyzoites was recognized by polyclonal antibodies against rTgH4, as indicated by immunoblotting analysis. Immunofluorescence assay showed that TgH4 binds to macrophages. Following incubation with rTgH4, the toll-like receptor 4 (TLR4) level of the macrophages was downregulated. Meanwhile, chemotaxis and the proliferation of macrophages were inhibited. However, rTgH4 can promote phagocytosis, apoptosis, and the secretion of nitric oxide, interleukin-6, and tumor necrosis factor-α from macrophages. Just 80 μg/ml rTgH4 can significantly elevate the secretion of interleukin-10 and interleukin-1β (p < 0.05 and p < 0.01). Viewed together, these outcomes indicated that rTgH4 can affect the functions of murine macrophages in vitro.