B-E8 (IL-6), together with IL-4, IL-5, IL-9 and IL-10 is produced by Th2 cells and is involved in antibody production, as well as protective responses to parasites and allergens. IL-6 may also be produced by monocytes and macrophages in response to bacterial infection. Increased serum IL-6 is found in an hepatic acute-phase response, and correlates with mortality in patients with sepsis. IL-6 may also be produced by fibroblasts, B cells, endothelial cells and several tumor cells.

IL-6 may be both a growth factor and differentiation factor for B cells. IL-6 is a potent myeloma cell growth factor for patients with multiple myeloma (MM), allowing the generation of myeloma cell lines whose proliferation is completely dependent on exogenous IL-6.