[Toll-like receptor 4 expression and cytokine secretion in microglial cells induced by IgG stimulation]

To investigate the effects of immunoglobulin G (IgG) on the expression of toll-like receptor 4 (TLR4) and secretion of cytokines in microglial cells in vitro.

Cultured primary rat microglial cells were stimulated with different concentrations of rat IgG (2 mg/L, 20 mg/L, 200 mg/L) and lipopolysaccharide (LPS) 10 mg/L for 24 h, respectively. The TLR4 expression in the microglial cells was examined by immunofluorescence staining and tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma) levels in the culture medium were assayed by ELISA.

IgG stimulation induced a significant TLR4 expression and TNF-alpha secretion in cultured microglial cells in a dose-dependent manner, while IFN-gamma was not detected in the same medium samples. As a positive control, LPS caused increases of TLR4 expression and both IFN-gamma and TNF-alpha production in the microglial cells.

TLR4 expression could be induced in microglia in vitro by non-pathogenic protein, IgG from the same species. Therefore, congeneric IgG stimulation might lead to proinflammmatory cytokine production, probably via MyD88-dependent pathway. This finding suggests that TLR4 may play more roles than pathogen recognition of innate immune reactivity, at least in the central nervous system.