In vitro studies on lymphocyte Fc gamma receptor blocking factors in human renal transplantation

The FcgammaRIIa polymorphism in patients with chronic kidney graft rejection

The FcgammaRIIa receptors, which provide a crucial link between cellular and humoral components of the immune response, display allelic polymorphism. Individuals are homozygous for either arginine 131 (RR131) or histidine 131 (HH131) or are heterozygous for these two alleles (RH131). The HH131 genotype binds human IgG2 with high RR131 with low, and RH131 with intermediate affinity. The aim of the study was to evaluate the FcgammaRIIa polymorphism in patients with chronic kidney graft rejection. The study included 121 renal transplant recipients: 53 patients with long-term stable graft function and 68 with chronic allograft rejection. The distribution of FcgammaRIIa genotypes in patients with chronic kidney graft rejection did not differ significantly from that in patients with stable graft function. The results suggest that the FcgammaRIIa polymorphism is not an important genetic risk factor for chronic rejection of kidney allografts.

Detection of lymphocyte Fc gamma receptor-blocking factors by the EA rosette inhibition assay. Refinement of the conventional method and development of a novel flow-cytometric assay

Serum factors which interact with human peripheral blood lymphocyte Fc gamma receptors (Fc gamma Rs) may be detected in vitro by the EA rosette inhibition assay (EARIA). This assay has been used to detect circulating immune complexes and certain alloantibodies directed against cell surface antigens situated in close proximity to Fc gamma Rs. Three main types of FcR-blocking factor have been demonstrated by the EARIA in human serum following exposure to alloantigens. A strong correlation was observed between the presence of one of these FcR-blocking factors (FcBF1) and human renal allograft survival. This factor was previously shown to bind preferentially to CD32+ B cells and to inhibit antibody synthesis. In this study we have shown that detection of FcBF1 by the EARIA depends on the type of erythrocyte and on the amount of antibody used to sensitise the erythrocytes. Furthermore, we have developed a flow-cytometric version of the EARIA which is rapid, reproducible and, most importantly, objective. Inter-laboratory comparisons using this standardised EARIA should now be possible.

Fetal-maternal immune interaction: blocking antibody and survival of the fetus

In the late 1940s it became clear that the homograft reaction was essentially the result of an immune response. Subsequently, Medawar commented on the apparent paradox of the survival of the mammalian fetus in the face of such a potential (cell-mediated) immune response. In an outbred population the fetal-placental unit will be antigenically different to the mother by virtue of its complement of paternal genes and additionally there may be developmental or stage-specific gene products that are immunogenic. Many mechanisms have been proposed to account for the survival of the fetus in the face of a potential immune attack and, while many of these have been investigated in considerable detail, there has been no clear-cut indication that any one plays a predominant role. Either control of immune rejection of the fetus is exercised by an as yet undiscovered mechanism or, more probably, by a combination of some or all of the mechanisms that have been proposed by many workers over the last three decades. Potential controlling processes, which will be reviewed briefly, include: systemic and local modification of maternal responsiveness; altered expression of MHC antigens on extra-embryonic tissues; the placenta as a barrier; and blocking antibody responses. We discuss some of our recent studies in which we have started to look for potential blocking antibodies in a mouse model system. Cells secreting immunoglobulins M and G, characterized in hemolytic plaque assays, have been mapped to areas close to the midgestation mouse embryo, using an immunocryohistological technique. A scaled-down version of hybridoma technology has been used as an analytical probe of the specificity and isotype of immunoglobulin secreted by cells originating either from close to the embryo/fetus or from the para-aortic lymph nodes (PALN). So far monoclonal (IgG1) antibodies with specificity for embryonic cells have been derived together with some monoclonal immunoglobulins with as yet uncharacterized antibody specificity.

Isolation and characterization of a high molecular weight lymphocyte Fc gamma receptor-blocking factor associated with renal allograft survival

We have confirmed our previous observation that improved human renal allograft survival is associated with the presence in pre-transplant serum of a high molecular weight lymphocyte Fc gamma receptor-blocking factor. Serum fractionation studies suggest that this factor is a complex protein consisting of IgG together with an IgG-binding protein which has an apparent molecular weight of approximately 60 kD.