In vitro delayed hypersensitivity granuloma formation: development of an antigen-coated bead model.

Previously, we have described an in vitro model of granulomatous hypersensitivity around Schistosoma mansoni eggs in both the murine model of schistosomiasis and in human schistosomiasis. These studies describe a new model of in vitro granuloma formation that complexes soluble egg antigen from S. mansoni eggs, a partially purified protein derivative of Mycobacterium tuberculosis (PPD), or bovine serum albumin to carrier beads. Ultrastructural and morphologic evaluations demonstrate that there are initial macrophage interactions, followed by the recruitment of antigen-specific T cells that interact with and recruit macrophages, lymphocytes, granulocytes, and fibroblasts. Finally, there is a stage of granulomatous organization involving fibroblast proliferation and collagen deposition. The in vitro reactivity, defined by a quantitative granuloma index, correlates with in vivo granulomas around S. mansoni eggs in the livers of infected cell donor animals. In vitro granuloma formation against PPD-coated beads correlated with delayed cutaneous hypersensitivity against PPD, which was judged by footpad swelling. The reactions demonstrate antigenic specificity and were intrinsically modulated in a manner that is analogous to that previously shown with the in vitro egg granuloma model. This model of in vitro granuloma formation promises to be a useful tool for elucidating mechanisms of cellular immunity and regulation.