Urinary detected renal antigens in the early diagnosis of kidney graft rejection

Changes of urinary alpha1-microglobulin in the assessment of prognosis in renal transplant recipients

BACKGROUND

After transplantation, even if the graft starts functioning immediately, there are morphological and functional changes in tubular structures. In addition, acute allograft rejection causes damage in the tubular epithelium, tubular basement membrane, and intertubular connective tissue. It also affects the functional capacity of proximal tubular cells resulting in impaired reabsorption and thus increased urinary excretion of low molecular weight proteins.

METHODS

We present a double-antibody radioimmunoassay for determination of the concentration of alpha1-microglobulin (alpha1 M) in urine. It was used to measure urinary excretion of alpha1 M approximately once a week during the first 1-6 posttransplant weeks in 136 consecutive patients: 30 patients developing acute rejection (75 24-hr urine samples) and 106 patients with stable graft function (223 24-hr urine samples). The results are expressed as alpha1 M/creatinine ratios.

RESULTS

Approximately 8 days after transplantation the mean (+/-SD) urinary alpha1 M/creatinine ratio of all patients was 17.0+/-14.8 mg/mmol, being about the same both in patients with uncomplicated posttransplantation course (16.3+/-14.0 mg/mmol) and in those who later developed rejection (19.3+/-15.1 mg/mmol), but about 60-fold higher than in healthy controls (0.27+/-0.15 mg/mmol). At that time, when all patients were included there was a correlation (r=0.3465, P<0.001) between alpha1 M/creatinine ratio and duration of cold ischemia. Thereafter, during the second week alpha1 M/creatinine ratio decreased in 89% of patients with stable graft function, but only in 14% of patients who later developed rejection (P<0.001). On the contrary, a significant increase (P<0.01) of alpha1 M/creatinine ratio was observed 4 to 1 day before rejection in all 15 patients, who had urines collected at that time. At the end of the follow-up period, alpha1 M/creatinine ratio in patients with rejection was 3-fold compared with the nonrejecting patients, and 100-fold compared with the healthy controls.

CONCLUSION

These results show that cadaveric transplantation results in impaired low molecular weight protein reabsorption, the degree of dysfunction relating to the duration of cold ischemia, and suggest that during the posttransplant weeks decreasing alpha1 M/creatinine ratio in consecutively collected urine samples indicates improved tubular function and in most cases rules out development of acute rejection.

Expression of human minor histocompatibility antigen on cultured kidney cells

Incompatibility of human minor histocompatibility (hmH) antigens can induce rejection of grafts in organ transplantation and graft-versus-host reactions in bone marrow transplantation. In spite of their importance in clinical transplantation, hmH antigens are not well studied. Previous studies have demonstrated the expression of hmH antigens on T and B cells, hematopoietic progenitor cells and keratinocytes. We have for the first time demonstrated the expression of hmH antigens on cultured kidney cells using HLA-B35-restricted, hmH antigen-specific cytotoxic T lymphocyte (CTL) clones, which were previously established from a patient who rejected two kidneys from HLA-identical sisters. The CTL clones could not kill cultured kidney cells. Since cultured kidney cells expressed very low levels of HLA class I antigens it was thought that their failure to be killed by the CTL clones was due to lack of expression of HLA-B35 antigens. After induction of class I antigens on cultured kidney cells by interferon-gamma (IFN-gamma), the IFN-gamma-treated cultured kidney cells were killed by the CTL clones. Furthermore, we isolated hmH antigens as peptides from cultured kidney cells after treatment with IFN-gamma. These results indicate that cultured kidney cells express hmH antigens when HLA class I antigen is induced by IFN-gamma and hmH antigens on cultured kidney cells are recognized by T cells as peptides presented by HLA-B35 molecules.