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 graft-vs-host disease (cGVHD). Interactions between these cell types were examined in both murine and human cGVHD models. To this purpose, cell supernatants from mice or humans with cGVHD and from controls were incubated for 6 days with either rat peritoneal MCs cocultured with 3T3 fibroblasts or with 3T3 fibroblasts alone. Supernatants in the murine model were of splenocytes from either mice with cGVHD or syngeneic controls (B → B). Supernatants in the human model were of peripheral blood mononuclear cells (PBMC) from cGVHD patients. Two groups of controls were used in the human model - patients who had undergone bone marrow transplantation (BMT) without developing cGVHD and patients with hematological malignancies who had not undergone bone marrow transplantation (pre-BMT). Histamine release was measured in MC/fibroblast cocultures incubated with the cell supernatants. Prostaglandin E₂ (PGE₂) and [³H]-thymidine incorporation were measured in both MC/fibroblast cocultures or 3T3 fibroblasts alone, incubated with the cell supernatants. In the murine model, the cGVHD supernatant caused significantly more histamine release from MCs than the syngeneic supernatant or medium alone. Moreover, cGVHD and syngeneic supernatants, compared with medium alone, inhibited 3T3 fibroblast proliferation. PGE₂ production by 3T3 fibroblasts was higher after incubation with the cGVHD supernatant than with the syngeneic supernatant or in medium alone. Incubation of fibroblasts with supernatants and indomethacin decreased PGE₂ production and increased [³H]thymidine incorporation. In humans, PBMC supernatants from cGVHD patients, as well as from BMT and pre-BMT controls, also displayed histamine releasing activity when cocultured With rat MCs. As with the murine cGVHD splenocyte supernatant, the human cGVHD supernatant decreased fibroblast [³H]-thymidine uptake, but the presence of MCs in the culture abrogated this inhibitory effect. In addition, the human cGVHD supernatant was found to contain high levels of PGE₂ and interleukin-1β (IL-1β). The addition of neutralizing anti-IL-1β antibodies to the cGVHD supernatant partially inhibited its histamine-releasing activity. Skin biopsies of involved areas in cGVHD patients revealed significantly reduced numbers of MCs and showed signs of MC degranulation compared with biopsies from pre-BMT controls. Immunocompetent cell supernatants from both mice and humans with cGVHD increased basal histamine release by MCs and reduced fibroblast proliferation. The murine cGVHD supernatant also enhanced PGE₂ production by 3T3 fibroblasts. Our findings indicate that complex interactions between immunocompetent cells, MCs, and fibroblasts probably play a role in cGVHD pathogenesis.