Pulmonary reaction to intravenously injected polymer beads

Abstract

The purpose of this study was to characterize the foreign body reaction in the mouse lung following embolization of intravenously injected divinylbenzene copolymer beads. In contrast to usual surgical implantation, this model dissociates the local foreign body reaction to the beads (in the lung) from inflammation and repair of tissue injury associated with implantation (peripheral site of injection). Quantitative determinations of pulmonary granuloma area using light microscopic morphometric measurements on tissue sections confirmed that the intensity of pulmonary inflammatory reaction increased rapidly to a maximum at 48 h following injection, with a volume exceeding 10 times that of the bead; at this time, the cellular exudate was 90% polymorphonuclear leukocytes. Thereafter, the inflammatory reaction decreased in intensity, and individual lesions became progressively richer in mononuclear cells (60% at 4 days and greater thereafter). Determination of intra‐ and interobserver variability indicated that maximal data precision was attained by measurement of the cross‐sectional areas of as few as 10 granulomas in each of five animals for each set of specific experimental conditions. Collagen was undetectable in granulomas at 7 weeks and 6 months, suggesting that the usual fibrous capsule forming in response to surgically implanted biomaterials is largely caused by repair of surgical trauma. The volume of inflammatory exudate at 48 h was reduced 68–86% by the nonsteroidal antiinflammatory agents indomethacin, aspirin, and ibuprofen and the antiinflammatory steroid methylprednisolone. Thus, the pulmonary bead granuloma model is a quantitative, reliable, and economical approach to investigating some aspects of biomaterial/time interactions in the absence of superimposed surgical trauma.