Transient poration and cell surface receptor removal from human lymphocytes in vitro by 1 MHz ultrasound.

The study objective was to gain insight into ultrasound-induced, sub-lytic cell surface modifications. Two primary hypotheses were tested by flow cytometric methods; viz., sonication will: 1. remove all or part of a specific cell surface marker in lymphocytes surviving insonation, and 2. induce transient pores in the cell membranes of some surviving cells. RPMI 1788 human lymphocytes were exposed in vitro to 1-MHz, continuous-wave ultrasound (approximately 8 W/cm2 ISP) for 30 s, which lysed approximately 50% of the cells. Insonation: 1. altered cell morphology, increasing the population of cells of reduced size but high structure (designated as population R2), many of which were nonviable, and diminishing the population of cells of large size and high structure (designated as population R1), most of which were viable, 2. diminished the fluorescence signal from the pan B lymphocyte marker CD19 in populations R1 and R2 to equivalent extents, and 3. increased by approximately 7-fold the number of transiently permeabilized cells in R1, as evidenced by simultaneous uptake of propidium iodide and fluorescein diacetate. The results indicate that ultrasound-induced CD19 removal from R1 cells can occur without accompanying gross membrane loss. The cell morphology/mortality shifts indicate that the ultrasound-induced morphological change is associated with lethal membrane poration, suggesting that the diminished CD19 fluorescence signal from insonated R2 cells arises partly by simultaneous loss of membrane fragments, CD19 and cytoplasm.

Alterations of the interleukin-4 pathway in production of tolerance by mixed hematopoietic chimerism.

BACKGROUND: The induction of specific tolerance could prevent acute and chronic rejection, as well as immunosuppressive complications, in recipients of vascularized organ allografts. Mixed hematopoietic chimerism is one approach to allogeneic tolerance. In these studies we examined whether mixed chimerism can confer tolerance to heart allografts across major and minor histocompatiblity barriers. We also examined the transcription of cytokine genes within the allografts of tolerance animals and in cell culture. METHODS: Adult Lewis rats were lethally irradiated and reconstituted with a mixture of 50 x 10(6) T-cell depleted bone marrow cells. Chimeric animals received heterotopic donor strain and third-party heart allografts and were assessed daily for rejection. Another set of chimeras received heart allografts that were examined at varying time points for transcription of cytokine genes by reverse-transcriptase polymerase chain reaction. RESULTS: Median graft survival in control animals was 6 days. Graft survival in 11 mixed chimeras ranged from more than 165 to more than 274 days (p < 0.001), and no episode of rejection or graft-versus-host disease was observed. Examination of cytokine transcriptions revealed dramatic alterations in interleukin-4 transcription in vivo and in vitro. CONCLUSIONS: Alterations in cytokine gene transcription are descriptive of tolerance in this model. Mixed chimerism confers long-term unresponsiveness to heart allografts across major and minor histocompatibility barriers with desirable features for clinical application.

Prevention of chronic rejection and graft arteriosclerosis by tolerance induction.

Chronic rejection is a major cause of graft failure in solid organ transplants after the first year. A characteristic lesion in a variety of chronically rejecting organs is a fibrointimal proliferative arteriosclerosis. It has been speculated that approaches to tolerance induction may be effective in obviating not only acute, but also chronic, rejection. A picture of chronic rejection develops naturally in heart grafts transplanted from the Lewis-to-F-344 strain of rat. We examined whether tolerance induction by bone marrow transplantation and development of hematopoietic chimerism or tolerance induction by intrathymic inoculation of alloantigen could effectively prevent chronic rejection in an established model of chronic rejection. Bone marrow chimeras were developed in F-344 hosts by transplantation of T cell-depleted allogeneic marrow (TCD A BMT). Another set of F-344 hosts was inoculated with intrathymic allogeneic bone marrow cells. Heart grafts in these animals demonstrated tolerance for 120 days after transplantation. Control F-344 animals treated with a short course of cyclosporine consistently developed chronic rejection by 120 days following heart transplantation. Strikingly absent from the tolerant animals was any sign of graft arteriosclerosis, which was demonstrated in the vast majority of control animals. Analysis of cytokine mRNA profiles at 30 days following heart transplantation demonstrated differences between control and tolerant animals. These results suggest that tolerance induction can effectively prevent chronic rejection.

Induction of specific tolerance to small-bowel allografts.

BACKGROUND: The induction of specific tolerance would greatly improve survival and functional state of organ transplant recipients. One approach that has recently received attention is the creation of mixed hematopoietic chimerism through the transplantation of allogeneic and syngeneic T-cell-depleted (TCD) bone marrows. In these studies we examined whether tolerance to highly immunogenic small-bowel transplants could be induced by mixed allogeneic chimerism. Tolerance induction depends on the sharing of antigens between bone marrow cells and small-bowel tissue. METHODS: Adult Lewis rats were lethally irradiated and reconstituted with a mixture of 50 x 10(6) TCD bone marrow cells. Thirty days after reconstitution, animals were tested for chimerism by fluorescence-activated cell sorter analysis. Chimeric animals then received ACI heterotopic small-bowel allografts and were assessed daily for rejection. Small-bowel allograft survival was compared to three control groups: (1) untreated Lewis recipients, (2) irradiated TCD syngeneically reconstituted Lewis recipients, and (3) Lewis bone marrow recipients that did not develop chimerism. RESULTS: Median graft survival in control groups was 8 days. Graft survival in eight mixed chimeras ranged from more than 135 to more than 304 days (p < 0.0001), and no episode of rejection or graft-versus-host disease was observed. Mixed lymphocyte reactivity of chimeric lymphocytes confirmed in vivo observation of tolerance. CONCLUSIONS: Bone marrow cells share tissue-specific antigens with small-bowel cells to permit induction of tolerance.