Leptin is a protein produced from the ob gene or lep gene, and acts as both a hormone involved in metabolic function as well as a proinflammatory cytokine by inducing Th1 immune responses (Dunn et al.; La Cava; Newman & Gonzalez-Perez). Leptin is a member of the gp130 family of cytokines and is known to be correlated with obesity (Dixit et al.; Dunn et al.). Leptin can both promote osteogenesis via osteoblast receptors and inhibit it through its actions on the hypothalamus (Figenschau et al.). It is a small, non-glycosylated protein with a highly conserved sequence between species. Leptin binds to the leptin receptor OB-R, which exists in six isoforms in humans and can activate various Janus kinase (JAK) and downstream pathways (Dunn et al.; Münzberg & Morrison; Newman & Gonzalez-Perez). For example, the binding of leptin to LepRb receptor activates JAK2, which leads to the phosphorylation of both JAK2 and the LepRb receptor, with three separate residues on the receptor triggering signaling pathways for SHP-2, STAT5, and STAT3 (Dunn et al.; Münzberg & Morrison). In addition to its effects on mature immune cells, other studies have suggested impacts on other cell types, with activities such as inducing cell proliferation and morphological differentiation in hematopoietic cell lines, chondrocytes, and hepatic cells (Figenschau et al.; Gainsford et al.; Santos-Alvarez et al.; Wang et al.).