Osteoclast Activating Factor is Distinct from the Monokine IL-1

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Abstract
Little is known about the cellular interactions involved in the production of the cytokine osteoclast activating factor (OAF) Recently, we have shown that the interactions between Thyl+ T cells and la+ macrophages during lectin stimulation are required for OAF secretion (1) In addition to OAF, a variety of other lymphokines (IL-2 and interfcron) and monokines (IL-1) are released under these conditions. It has been reported that partially purified IL-1 can induce ostcoclastic bone resorption in vitro (2) Since macrophages are required for OAF production and are the source of IL-1, it became important to determine the relationship between these two factors. We have used the differential sensitivity to the immunosuppressive drug cyclosponn A (CsA) as a tool to distinguish these factors Our results demonstrate that 1. CsA inhibits IL-2 production, 2. CsA fails to inhibit either the normal, basal level of bone resorption nor OAF induced resorption, 3. CsA blocks the production of OAF if added pnor to cell ‘activation’. Activation renders cells insensitive to the effects of CsA, 4. CsA fails to block IL-1 production These data suggest that OAF is distinct from IL-1, although they are both capable of inducing bone resorption under the appropriate conditions. OAF appears to be of lymphocyte origin and primarily responsible for bone resorption Cyclosponn A may be used as a tool to dissect the cellular interactions involved in cytokine production

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