REGULATION OF THE FUNCTIONAL-ACTIVITY OF MAST-CELLS AND FIBROBLASTS BY MONONUCLEAR-CELLS IN MURINE AND HUMAN CHRONIC GRAFT-VS-HOST DISEASE

Mast cell (MC)-fibroblast-immunocompetent cell interactions may play a role in the inflammatory and fibrotic processes present in chronic gr aft-vs.-host disease (cGVHD). Interactions between these cell types we re examined in both murine and human cGVHD models. To this purpose, ce ll supernatants from mice or humans with cGVHD and from controls were incubated for 6 days with either rat peritoneal MCs cocultured with 3T 3 fibroblasts or with 3T3 fibroblasts alone. Supernatants in the murin e model were of splenocytes from either mice with cGVHD or syngeneic c ontrols (B --> B). Supernatants in the human model were of peripheral blood mononuclear cells (PBMC) from cGVHD patients. Two groups of cont rols were used in the human model-patients who had undergone bone marr ow transplantation (BMT) without developing cGVHD and patients with he matological malignancies who had not undergone bone marrow transplanta tion (pre-BMT). Histamine release was measured in MC/fibroblast cocult ures incubated with the cell supernatants. Prostaglandin E(2) (PGE(2)) and [H-3]-thymidine incorporation were measured in both MC/fibroblast cocultures or 3T3 fibroblasts alone, incubated with the cell supernat ants. In the murine model, the cGVHD supernatant caused significantly more histamine release from MCs than the syngeneic supernatant or medi um alone. Moreover, cGVHD and syngeneic supernatants, compared with me dium alone, inhibited 3T3 fibroblast proliferation. PGE(2) production by 3T3 fibroblasts was higher after incubation with the cGVHD supernat ant than with the syngeneic supernatant or in medium alone. Incubation of fibroblasts with supernatants and indomethacin decreased PGE(2) pr oduction and increased [H-3]-thymidine incorporation. In humans, PBMC supernatants from cGVHD patients, as well as from BMT and pre-BMT cont rols, also displayed histamine releasing activity when cocultured with rat MCs. As with the murine cGVHD splenocyte supernatant, the human c GVHD supernatant decreased fibroblast [H-3]-thymidine uptake, but the presence of MCs in the culture abrogated this inhibitory effect. In ad dition, the human cGVHD supernatant was found to contain high levels o f PGE(2) and interleukin-1 beta (IL-1 beta). The addition of neutraliz ing anti-IL-1 beta antibodies to the cGVHD supernatant partially inhib ited its histamine-releasing activity. Skin biopsies of involved areas in cGVHD patients revealed significantly reduced numbers of MCs and s howed signs of MC degranulation compared with biopsies from pre-BMT co ntrols. Immunocompetent cell supernatants from both mice and humans wi th cGVHD increased basal histamine release by MCs and reduced fibrobla st proliferation. The murine cGVHD supernatant also enhanced PGE(2) pr oduction by 3T3 fibroblasts. Our findings indicate that complex intera ctions between immunocompetent cells, MCs, and fibroblasts probably pl ay a role in cGVHD pathogenesis.