HLA-G has a concentration-dependent effect on the generation of an allo-CTL response.

Human leucocyte antigen (HLA) -G is expressed on trophoblast cells during pregnancy, suggesting a role in protection of the semiallogeneic fetus. Published data suggest that HLA-G protects a cell against natural killer cell lysis. It has been hypothesized that HLA-G may also protect the fetus by preventing allo-cytotoxic T lymphocyte (CTL) responses. To test this hypothesis, we assayed the effects of various concentrations of purified HLA-G on CTL response in a mixed lymphocyte culture (MLC) system. We found that concentrations > or =0.1 microg/ml of HLA-G suppressed the allo-CTL response by 30-100% over the control, but, paradoxically, concentrations of 0.01-0.05 microg/ml of HLA-G augmented the allo-CTL response by 25-50% over the control. Concentrations < or = 0.001 microg/ml HLA-G had no effect. Addition of HLA-G to preprimed allo-CTL effector cells did not affect their killing ability. Allo-CTL suppressive doses of HLA-G induced a T helper type 2 (Th2) cytokine response, whereas allo-CTL-enhancing doses of HLA-G induced a Th1-type cytokine response. HLA-G purified from first-trimester placenta does not affect allo-proliferative responses nor does it alter the percentage of CD4+ or CD8+ T cells in MLCs. These findings support a potential role for HLA-G-mediated suppression of allo-CTL formation in normal pregnancies. In addition, the effects observed at lower concentrations of HLA-G may have interesting implications for the condition of pre-eclampsia in which concentrations of this HLA class I molecule are reduced.

Gender disparity in living renal transplant donation.

Numerous studies document that women constitute the majority of living kidney donors, but the reasons behind the disparity in donation rates between men and women remain obscure. We studied this issue by gathering data on family members of living donor allograft recipients at a single large center over a 5-year period (n = 144). By considering all potential donors (spouses and first-degree relatives) within each recipient's immediate family, we determined that men and women are excluded as donors at approximately similar rates on the basis of medical condition or known blood group type A, type B, type O incompatibility, and that a greater percentage of acceptable female donors (28.3%) compared with men (20.3%) go on to donate a kidney (P: = 0.027). However, when only first-degree relatives are considered, the difference in donation rate between men and women becomes nonsignificant (26.9% of women versus 22.2% of men; P = 0.229). Among spouses, the gender disparity in donation rate is greater (36% of wives versus 6.5% of husbands who are acceptable donors go on to donate a kidney; P = 0.003). Evidence that economic factors may contribute to the overall gender disparity is also presented. In conclusion, the gender disparity among living kidney donors observed in our population can be largely attributed to an overwhelming predominance of wives among spousal donors. Possible explanations and potential interventions to address underrepresentation of male donors are discussed.

Clinical practice guidelines: prevention of cytomegalovirus disease after renal transplantation.

OBJECTIVE: To develop a set of comprehensive, standardized, evidence-based guidelines for the use of antiviral therapy to prevent cytomegalovirus disease in adult patients having undergone renal transplantation. OPTIONS: The use of medication, at the time of induction therapy or at the earliest sign of viremia. Treatments were evaluated by patient and donor serologic groups and the induction regimen used. OUTCOMES: The control of symptoms and features of cytomegalovirus disease over the first 6 mo to 1 yr after transplantation. EVIDENCE: Articles, compiled using a MEDLINE search from 1976 to July 1997, were reviewed by representatives of nephrology, microbiology, pharmacy, and epidemiology. Additional information was obtained from recent review articles and conference abstracts, and from experts in the field. VALUES: The evidence-based methods and values of the Canadian Task Force on the Periodic Health Examinations were used. High value was placed on studies with a randomized controlled design and blinded outcome observers. Study quality was classified as poor when cointervention was present (especially with regard to immunosuppressive regimens), when more than 20% of patients were lost to follow-up, and when intention to treat analysis was not performed. Recommendations were made with a graded system (grades A and B: Use of the intervention advised, based on high or fair quality evidence, respectively; grades D and E: Use of the intervention not advised, based on high or fair quality evidence, respectively: grade C: No recommendation made because of insufficient or conflicting evidence). RECOMMENDATIONS: (1) Seropositive recipient; donor seropositive or seronegative; immunosuppression with antilymphocyte products. Prophylaxis with antiviral therapy recommended (grade A recommendation). (2) Seronegative recipient; seropositive donor; immunosuppression with antilymphocyte products. Prophylaxis with antiviral therapy recommended (grade A recommendation) (3) Seronegative recipient; seropositive donor; conventional immunosuppression. Prophylaxis with antiviral therapy recommended (grade B recommendation). (4) Seronegative recipient; seronegative donor; any immunosuppressive regimen. No prophylaxis with antiviral therapy required (grade D/E recommendation). (5) Seropositive recipient: donor seropositive or seronegative; conventional immunosuppression. Prophylaxis left to the discrimination of the physician in charge (grade C recommendation).

Time-dependent induction of protective anti-influenza immune responses in human peripheral blood lymphocyte/SCID mice.

The human (hu) PBL/SCID mouse model has the potential to provide a powerful tool for the study of human immune function. However, at peak engraftment (4-8 wk postinjection), recovered human T cells are largely unresponsive to foreign Ag and have converted to an activated/memory-type phenotype. Here we show that this conversion is not a prerequisite for engraftment because at early stages (2 wk) a substantial fraction of human T cells detected in SCID peripheral blood retains the unactivated/naive phenotype of donor PBL. This early stage is also associated with a TCR repertoire in both the CD4 and CD8 subsets that is similar to that in the donor. Importantly, we show that strong HLA class I allele- and peptide-specific cytotoxic T lymphocyte as well as humoral responses can be generated in this model when human cells encounter Ag (infection with influenza A) at early, but not late, stages in engraftment. This early human response was also functional, as partial protection against influenza-induced pathology and death in SCIDs was observed. Taken together, these results demonstrate that the huPBL/SCID model can support the generation of potent and specific CTL and humoral responses provided that Ag is introduced early, presumably before the time-dependent generalized xenoactivation of engrafted human cells.

Characterization of a cis-acting regulatory element which silences expression of the class II-A beta gene in epithelium.

Class II major histocompatibility complex (MHC) genes encode for alpha/beta chain pairs that are constitutively expressed principally on mature B cells and dendritic cells in mice. These gene products are easily induced on macrophages with cytokines, and may also aberrantly appear on the surface of epithelium during immune injury. The appearance of class II determinants in parenchymal tissue potentially renders these somatic cells capable of antigen presentation to circulating CD4+ T lymphocytes, and their absence may be protective for normal tissues expressing self-antigens. The low surface class II expression observed on parenchymal cells generally correlates with low levels of mRNA, suggesting that transcription rate is a major element in class II regulation. To understand the transcriptional mechanism maintaining low basal surface expression of class II in somatic cells, we transiently transfected mini-gene reporter constructs to study the regulation of the murine A beta promoter in a cultured renal epithelial cell line. We describe here a negative cis-acting regulatory region located between -552 and -489 bp upstream of the A beta cap site that silences the transcriptional activity of the A beta promoter in epithelial cells in an orientation-dependent manner, and is also able to silence a heterologous promoter. This region is not active in class II-expressing B cells (BAL-17) in culture, but is functional in two other murine class II-negative cell lines, fibroblasts and thymoma T cells. Using competition electrophoretic mobility shift assays, we have localized the core protein binding site within this region to an 8-10-bp response element, designated A beta NRE, at -543 to -534 bp. A nuclear extract from BAL-17 cells does not bind to this element. Mutation of this site abrogates the transcriptional silencing activity of the region. We conclude that the transcription of class II-A beta in parenchymal cells, and some lymphocytes, can be actively repressed by an upstream silencing element.

The nephritogenic immune response.

Recent work has improved our understanding of a number of aspects of the nephritogenic immune response. Progress has been made in the understanding of the development of idiotypic networks, and in understanding the structural nature of the targets of self-reactive T cells and the paracrine mediators that are released as part of the local inflammatory response.

Analysis of the cDNA sequence encoding MHC-A beta in tubular epithelium from mouse kidney.

Class II gene products of the major histocompatibility complex (MHC) are not expressed usually in abundance on normal epithelium. The cell surface visibility of such proteins for the immune system is thought to be limited protectively in order to minimize inflammation consequent to the recognition of self-antigens in parenchymal structures by T lymphocytes. In the current experiments we investigated whether the previously recognized sparseness of A beta on the surface of tubular epithelial cells might be accounted for by a protein coding difference deduced from the primary structure of its transcript compared with sequence from lymphoid cells that normally express A beta in generous amounts. We demonstrate, however, using clones obtained from a cDNA library prepared from tubular epithelium harvested from H-2s (A beta/alpha+; E beta/alpha-) mice susceptible to autoimmune interstitial nephritis, that the nucleotide sequence encoding the class II A beta chain in cells from both compartments is essentially identical. Our findings suggest that there is no primary structural aberrancy in the coding region of parenchymal A beta that would contribute to its low expression. The protective tolerance afforded by reduced numbers of class II molecules in normal tissues is, therefore, more likely the result of repressive regulatory processes.