IN VIVO MECHANISMS OF ALLOREACTIVITY

Abstract

The in vivo generation of donor-specific alloantibody was examined using a sponge matrix allograft model. This experimental model has not been previously used to study the humoral immune response during allograft rejection. We chose this model on the basis of its ability to permit recovery of antibody directly from the graft site without the use of elution and dialysis protocols. C57BL/6 (H-2b) mice were implanted with polyurethane sponges injected with DBA/2 (H-2d) splenocytes, C57BL/6 splenocytes, or phosphate-buffered saline (PBS). Thirteen days later, only those sponges injected with allogenic (DBA/2) splenocytes contained high levels of complement-dependent donor-reactive cytolytic antibody. Donor-reactive cytotoxic antibody was detected by its ability to lyse donor-derived target cells but not host-derived target cells. In contrast, cell-free control sponges injected with PBS or syngeneic sponges injected with C57BL/6 splenocytes contained no detectable H-2d-reactive cytolytic activity. Donor specificity of sponge fluid antibody was determined by removal of H-2d cytotoxic activity following absorbtion with DBA/2 thymocytes. Control absorptions with C57BL/6 or third-party C3H/HeJ thymocytes were ineffective in removing this activity. To determine the rate at which antibody would accumulate in sponge implants we examined the sponges for antibody activity at varying times following implantation. Detectable levels of donor-specific antibody were observed as early as 7 days postimplantation. Antibody activity in the sponges subsequently increased to maximal levels by day 10, and was maintained through day 17, which was the last day examined. An accelerated rate of antibody accumulation was observed in alloimmune recipients, which had previously rejected DBA/2 skin grafts. To determine whether antibody activity observed in the sponge fluid reflected similar activity present in the circulation, we compared donor-reactive antibody activity in sera and sponge fluids from the same recipients on various days following sponge implantation. In this experiment donor-specific cytotoxic antibody was first detected in both the sponge fluids and sera on day 10, although the level of activity was higher in the sera than in the sponge fluids. Levels of cytotoxic antibody in sponge fluids remained constant through day 14, and cytotoxic antibody activity in the sera decreased by day 14 to levels observed in the sponge fluids. The cytotoxic antibody activity in sponge allograft fluids paralleled the accumulation of donor-reactive IgM, rather than the accumulation of total donor-reactive antibody.(ABSTRACT TRUNCATED AT 400 WORDS)