This may suggest that another key chemoattractant player is important for eliciting macrophage infiltration given the absence of macrophages in the high MCP-1-expressing ad-12/15-LO fat, a possibility supported by the observation that MCP-1 knockout mice still exhibit obesity-induced macrophage infiltration into adipose tissue [34]. This evidence concerns the gene CCL2 and obesity due to melanocortin 4 receptor deficiency.