Through binding to the interleukin-5 receptor, interleukin 5 stimulates B cell growth and increases immunoglobulin secretion—primarily IgA.

Unlike other members of this cytokine family (namely interleukin 3 and GM-CSF), this glycoprotein in its active form is a homodimer.

IL-5 is also expressed by eosinophils[8] and has been observed in the mast cells of asthmatic airways by immunohistochemistry.

The principal role of these cells, in a healthy host, is the elimination of antibody bound parasites through the release of cytotoxic granule proteins.

In Hodgkin lymphoma, the typically-observed eosinophilia is thought to be attributable to an increased production of IL-5.