Brief Definitive Report Administration of Recombinant Interleukin 2 in Vivo Induces a Polyclonal Igm Response

IL-2 is a T cel l -der ived soluble factor with a broad spectrum of growth and d i f fe ren t ia t ion-promot ing activities (1). It provides a signal for cell proliferat ion by binding to high-affinity receptors on responsive cell populations. IL-2 receptors are expressed by activated T cells, and their functional importance has been shown in vivo (2). Administrat ion of IL-2 in vivo specifically enhances allogeneic responses and allows induction o f cytotoxic and helper T cells in nude mice and in cyclophosphamide-treated animals (3-5). T h e recent finding (6) of IL-2 receptors on B cells suggest that IL-2 might also exer t a function as a B cell growth and differentiat ion factor. We wished to explore the functional role o f IL-2 in the initiation and different iat ion of a humoral immune response in vivo. IL-2 given in vivo could potentially affect humoral responsiveness by two different mechanisms: amplification o f B cell responses by expansion o f the helper cell pool, a n d / o r by direct stimulation of B cells. We repor t here that administration of rIL-2 in vivo caused polyclonal IgM product ion. T r e a t m e n t with rIL-2 clearly augmented the IgM product ion in pr imary as well as secondary immune responses, but it did not affect IgG secretion, nor did it induce a class switch f rom IgM to IgG in genetically low-responding mice.