Immunophenotypic analysis of leukocyte infiltration in the renal transplant

Natural killer cell subsets in allograft rejection and tolerance

PURPOSE OF REVIEW

To discuss the role of natural killer cells in regulating the survival of transplanted organs.

RECENT FINDINGS

Natural killer cells have been found to have the dual capacity to promote rejection of transplanted organs and be required for the induction of transplantation tolerance. In murine recipients of bone marrow transplants, or in CD28 recipients of cardiac allografts, different natural killer cell subsets have been shown to promote or delay rejection, depending on their major histocompatibility complex class I specificity. In mouse models of skin and islet allograft acceptance mediated by costimulation-targeting therapies, the presence of natural killer cells was found to be essential for long-term graft acceptance, perhaps due to their ability to eliminate donor or recipient immune cells.

SUMMARY

Natural killer cells can either accelerate or avert rejection in a manner that is influenced by both donor-recipient major histocompatibility complex disparity as well as the milieu created by costimulation-targeting therapies. In clinical settings, alloreactivity by defined natural killer cell subsets may be important in achieving tolerance, and the outcome of natural killer cell activity may be influenced by specific immunosuppressive regimens.

The changing role of natural killer cells in solid organ rejection and tolerance

Natural killer (NK) cells have emerged as a particular focus of interest in transplantation due to their ability to distinguish allogeneic major histocompatibility complex (MHC) antigens and their potent cytolytic effector mechanisms. Once relegated to the field of bone marrow transplantation, NK cells have recently been shown to participate in the immune response against solid organ allo- and xenografts. These new findings suggest that the role of NK cells in solid organ rejection and tolerance needs to be reexamined.

IFN-gamma, produced by NK cells that infiltrate liver allografts early after transplantation, links the innate and adaptive immune responses

The role of NK cells following solid organ transplantation remains unclear. We examined NK cells in acute allograft rejection using a high responder model (DA-->Lewis) of rat orthotopic liver transplantation. Recipient-derived NK cells infiltrated liver allografts early after transplantation. Since chemokines are important in the trafficking of cells to areas of inflammation, we determined the intragraft expression of chemokines known to attract NK cells. CCL3 was significantly increased in allografts at 6 h post-transplant as compared to syngeneic grafts whereas CCL2 and CXCL10 were elevated in both syngeneic and allogeneic grafts. CXCL10 and CX3CL1 were significantly upregulated in allografts by day 3 post-transplant as compared to syngeneic grafts suggesting a role for these chemokines in the recruitment of effector cells to allografts. Graft-infiltrating NK cells were shown to be a major source of IFN-gamma, and IFN-gamma levels in the serum were markedly increased, specifically in allograft recipients, by day 3 post-transplant. Accordingly, in the absence of NK cells the levels of IFN-gamma were significantly decreased. Furthermore, graft survival was significantly prolonged. These data suggest that IFN-gamma-producing NK cells are an important link between the innate and adaptive immune responses early after transplantation.

Identification, cloning, and characterization of a novel rat natural killer receptor, RNKP30: a molecule expressed in liver allografts

BACKGROUND

As a component of the innate immune system, natural killer (NK) cells may play a significant role in the early events after solid-organ transplantation. Activated NK cells have been shown to infiltrate allografts in transplant models. To better understand NK cells and the role of NK cell receptors in transplantation, we have cloned and begun characterizing a novel rat molecule, rNKp30.

METHODS

RNKp30 cDNA was cloned by 5' rapid amplification of cDNA ends polymerase chain reaction (PCR) and reverse transcriptase (RT)-PCR from mononuclear cells infiltrating a rejecting liver allograft. Southern blot analysis was used to determine the rNKp30 gene copy number. RT-PCR and Northern blotting were used to examine rNKp30 RNA expression in NK cells, multiple tissues, and liver grafts. Immunocytochemistry, immunoprecipitation, and Western blot analysis with two anti-rNKp30 polyclonal antibodies, CA680 and CA1071, were performed. Tunicamycin and endoglycosidase treatments determined the extent of rNKp30 glycosylation.

RESULTS

RNKp30 is homologous to human and macaque NKp30. It is a single copy gene with five identified single-nucleotide polymorphisms. RNKp30 is expressed by NK cells and is detectable as a single transcript by Northern blot in normal spleen, lymph node, and lung tissues. RNKp30 is a variably N-glycosylated cell surface molecule with a protein backbone of approximately 21 kDa. Elevated transcript expression of rNKp30 is detected in both rejected and spontaneously accepted liver allografts, but not in syngeneic or cyclosporine A-treated allografts.

CONCLUSIONS

RNKp30 is a glycosylated surface NK cell receptor with limited polymorphism. This putative activation receptor is expressed in liver allografts and may participate in the innate immune response after transplantation.

New intra-renal graft genes associated with tolerance or rejection

BACKGROUND

Recipient type mononuclear cells infiltrating kidney allografts have different phenotypes and functions according to the fate of the graft. We hypothesized that different genetic programs were involved in rejected or accepted tissues and thus, transcripts that correlated with the clinical status could be identified by a differential expression strategy. This strategy was applied to miniature swine class II matched, class I disparate kidney grafts, which are accepted in recipient animals treated for 12 days with Cyclosporin A (CsA).

METHODS

The mRNA differential display RT-PCR technique (DDRT-PCR) was used to detect clinical status-specific transcripts. cDNA templates for this analysis were derived from biopsies of accepted (CsA treated) and rejected (untreated) kidney grafts 8 days post-transplantation.

RESULTS

A first screening procedure identified 23 PCR products differentially amplified in either tolerant or rejector samples. Nucleotide sequence of these partial transcripts showed that 11 out of 23 (48%) sequences had unknown open reading frames while 12 had substantial homology to known sequences. To validate the approach, rejection-associated (RA) cDNA 1 (RA-1) was characterized further. The results indicated that RA-1 is the porcine equivalent of secreted protein acidic and rich in cysteine (SPARC). Expression studies demonstrated that upregulation of SPARC gene transcription preceded other indicators of kidney dysfunction and correlated with the extent of graft infiltration.

CONCLUSION

DDRT-PCR appears to be a powerful technique to identify genes differentially expressed in grafted tissues that correlate with tolerance or rejection. One of the gene transcripts identified through this method, SPARC, may be a reliable marker of tissue injury consequent to cellular infiltration and rejection.

Contribution of Renal Secreted Complement C3 to the Circulating Pool in Humans

Complement C3 produced within the kidney may be an important mediator of local inflammatory and immunological injury. The overall level of renal C3 production and consequently its contribution to the total circulating C3 level are, however, unknown. This was investigated by using the conversion of C3 from recipient to donor allotype following renal transplantation. The C3 F and S allotypes of 80 consecutive renal donor-recipient pairs (148 individuals) were determined by amplification refractory mutation system analysis. The extent of allotype conversion in C3 F/S mismatched recipients was quantified at different stages after transplantation, using an enzyme-linked immunosorbent assay specific for the HAV 4-1 polymorphism of C3 that is strongly associated with C3F. Twenty-one of the eighty recipients were potentially informative, i.e., were C3 SS recipients of C3 FF or FS donor kidneys. In the early postoperative period, donor-derived C3 (HAV 4-1-positive) was undetectable, increasing to 9.6% of the total circulating C3 at times of acute allograft rejection. When graft dysfunction occurred from causes other than rejection, donor C3 remained undetectable. After stable graft function was attained (3–13 mo after transplantation), donor C3 made up 4.5% of the total circulating C3 pool. Our findings demonstrate that human transplant kidney in the resting state is a significant source of extrahepatic C3. Its heightened local synthesis during rejection episodes suggests a possible pathogenic role for C3 in this immunological process.

Localization of C-X-C and C-C chemokines to renal tubular epithelial cells in human kidney transplants is not confined to acute cellular rejection

Chemokines are important mediators of leucocyte chemoattraction to inflammatory sites. Previous work has shown that the expression of some chemokines is upregulated during renal transplant rejection. The objectives of the present study were to determine whether chemokine expression is increased during renal transplant rejection. Immunohistochemistry was used to localize the C-X-C (alpha) chemokine interleukin-8 (IL-8) and the C-C (beta) chemokines monocyte chemoattractant protein-1 (MCP-1) and macrophage inflammatory protein-1beta (MIP-1beta) in 30 needle biopsies of human kidney transplants taken for diagnosis of renal dysfunction. Urine samples from transplant patients taken immediately prior to biopsy were assayed for chemokine content using enzyme-linked immunosorbent assays (ELISAs). Results from groups of patients having different clinicopathological diagnoses were then compared. All three chemokines were detected in most renal transplant biopsies showing acute cellular rejection but, although infiltrating leucocytes were often positive, staining was predominantly localized to renal tubular epithelium. Staining for MCP-1 was generally weaker than for the other chemokines, and collecting tubules were usually stained more strongly than proximal convoluted tubules. Tubular epithelial staining was also found in biopsies from patients without signs of acute cellular rejection. There were significantly higher amounts of IL-8 in the urine of patients with acute cellular rejection, even when patients with urinary tract infections were excluded, but mean titres of urinary MIP-1beta did not differ between patient groups. This was also found when titres were normalized for urine volume and creatinine levels. Production of IL-8, MCP-1 and MIP-1beta is not confined to kidney transplants showing acute cellular rejection, and may be a relatively nonspecific response of tubular epithelial cells to renal damage.

Molecular and cellular events implicated in local tolerance to kidney allografts in miniature swine

Long-term tolerance to class I-mismatched renal allografts can be induced in miniature swine by treatment with a short course of cyclosporine (CsA). Kidney recipients treated with CsA and untreated control kidney recipients both demonstrated infiltration of the transplanted kidney by mononuclear cells, which reached a maximum between postoperative days 8 and 11. Recipients that did not receive the tolerizing regimen rejected their grafts between postoperative days 8 and 12 in this model. The kinetics of cytokine gene expression, including interleukin (IL)-1alpha, IL-1beta, IL-2, IL-6, IL-10, tumor necrosis factor, and interferon-gamma (IFN-gamma), within the grafted kidney of rejector and acceptor animals, were determined using Northern blot hybridization. A strong correlation between rejection and up-regulation of the IFN-gamma gene was observed, whereas animals with long-term tolerance showed low levels of IFN-gamma, but high levels of IL-10 gene transcription. None of the other cytokine genes demonstrated a reproducible pattern of expression that correlated with acceptance/rejection of allografts. Analysis of transcription patterns of cytokine genes in mononuclear cells purified from renal grafts confirmed the initial observations made on biopsies. The phenotype of graft-infiltrating cells (GIC) showed a dominance of CD8+ cells, with an average of 66% single-positive cells and 19% CD4/CD8 double-positive cells, compared with 30% and 14%, respectively, for peripheral cells. Predominance of CD8+ GIC was dictated neither by the MHC antigen disparity nor the rejector/acceptor status. These results, therefore, suggest that GIC represent a regulated combination of mononuclear cells producing local immune mediators that, in part, control the fate of allografts in this large animal model.

Expression and tissue localization of donor-specific complement C3 synthesized in human renal allografts

Recent evidence suggests that the third component of complement, C3, is synthesized in renal tissue, and that increased C3 synthesis occurs in allograft rejection and immune complex-mediated nephritis. However, it is unclear whether intrinsic renal cells or migratory cells in the inflammatory infiltrate, possibly of recipient bone marrow origin, are the source of the C3 detected. This was investigated by determining the C3 allotypes of mRNA and protein produced by transplanted human kidney. Twenty donor-recipient pairs were examined, of which nine pairs had C3 allotypes that were informatively mismatched at the C3 F/S locus. Reverse transcriptase polymerase chain reaction (RT-PCR) followed by amplification refractory mutation system analysis showed intracellular donor-specific mRNA expression in six of these nine cases, at up to 61 days post-transplantation. Nested PCR reactions and the size of PCR products excluded contamination by genomic DNA. Allotype-specific staining of frozen sections of renal cortex demonstrated donor-derived C3 protein in both glomeruli and tubules of all biopsies examined, in a predominantly tubular distribution. These results imply that at least some of the pro-inflammatory effects of complement arise from intrinsic tissue synthesis of donor C3, and that this may represent a previously unrecognized source of tissue injury. The occurrence of local synthesis of C3 of donor allotype may have functional implications related to C3 allotype, and may also be relevant to strategies to inhibit intrarenal complement-mediated injury.