Interleukin-6 (IL-6) is an important pro-inflammatory cytokine, which plays critical roles in both innate and adaptive immunity. IL-6 is produced by a variety of different cell types, including macrophages, endothelial cells, and T cells. Its production can be initiated in response to microbial invasion or other cytokines, such as tumor necrosis factor alpha (TNF-alpha) and IL-1 beta. As part of the innate immune system, IL-6 acts on hepatocytes to induce expression of C-reactive protein, fibrinogen, and serum amyloid A, also known as the acute phase reactants. IL-6 also plays a key role in activating antibody-producing B cells to proliferate, leading to an enhanced antibody response.