Local pathological responses to slow-release recombinant interleukin-1, interleukin-2 and γ-interferon in the mouse and their relevance to chronic inflammatory disease

1. The present study describes the pathological responses to local administration of recombinant cytokines in subcutaneously implanted slow-release ethylene vinyl acetate (EVA) co-polymer in mice. 2. EVA-recombinant human interleukin-1β (10 4 units) implants induced the formation of chronic granulomatous inflammatory tissue between 4 and 7 days after implantation, characterized by predominant macrophage infiltration, neovascularization and fibrosis which persisted up to 21 days after-implantation. EVA-recombinant human interleukin-1α (10 4 –10 5 units) implants induced a qualitatively similar but less intense response. 3. In contrast, recombinant human interleukin-2 (10 2 –10 4 units) implants resulted in early lymphocytic vasculitis (4 days) and the development of a predominantly lymphoid lesion comprised of lymphoblasts and significant mononuclear cell proliferation by 7 days. 4. EVA-recombinant γ-interferon (10 3 –10 4 units) implants failed to elicit a significant tissue response; with the exception of multinucleate giant cell formation the characteristics of these lesions closely resembled the mild fibrotic responses observed for EVA-bovine serum albumin (0.5–12.5 mg) implants. 5. These observations suggest that continuous endogenous local release of interleukin-1 or interleukin-2 in vivo is sufficient for the development of specific pathological features characterizing chronic immuno-inflammatory diseases.