Monocyte chemoattractant protein-1 immunoreactivity in sensory ganglia and hindpaw after adjuvant injection.

Monocyte chemoattractant protein-1 (MCP-1)/CCL2 is a member of the CC chemokine family that exhibits potent chemotactic activity for monocytes/macrophages. In the current study, the proportion of monocyte chemoattractant protein-1-immunoreactive (IR) neurons in the dorsal root ganglion (DRG) of rats was shown to increase markedly following adjuvant injection into the hindpaw. MCP-1-IR axon terminals were not found in the spinal cord or hindpaw of control or adjuvant-treated rats. Instead, the inflamed hindpaw dermis was infiltrated by numerous MCP-1-IR inflammatory cells. Following adjuvant injection, the majority of MCP-1-IR neurons in the DRG colocalized with IB4 binding. Our findings suggest that peripheral tissue inflammation induces increased MCP-1 expression in DRG neurons and this may be dependent upon glial cell line-derived neurotrophic factor.