Interleukin 6 (IL-6) is a multifunctional cytokine that plays an important role in regulating immune and inflammatory responses. Produced by a wide variety of cells, including T cells, monocytes, fibroblasts, endothelial cells, and keratinocytes, IL-6 works by stimulating B-cell differentiation and antibody production, as well inducing expression of hepatic acute-phase proteins, regulating bone metabolism, and promoting neuronal differentiation. In addition, IL-6 appears to interact with IL-2 in the proliferation of T-lymphocytes and with IL-3 to promote the proliferation of multipotent hematopoietic progenitor cells. The Millipore mouse IL-6 ELISPOT Antibody Pair provides a sensitive and highly reliable method for the detection of IL-6 secreting cells at the single cell level.