Post-thymic T-cell development in the rat.

The presence or absence of CD4, CD8, Thy-1, RT6 and CD45RC revealed a number of T-cell subpopulations in the rat. Vascular thymus transplantation was used in RT7 congenics to establish the lineage relationship between these subpopulations by following phenotypic changes after thymus emigration. We found that recent thymic emigrants exhibit the Thy-1+/RT6-/CD45RC- phenotype and express either CD4 or CD8. Within 11 days after emigration, these cells differentiated into Thy-1-/RT6+/CD45RC+ cells. From 33 to 76 days following transplantation, a proportion of the latter lost RT6 and/or CD45RC expression, suggesting further differentiation. The pathway of 'mature' T-cell differentiation could be reconstructed from these data and analysis of the differences between T-cell subsets in thymectomized and normal control rats. End-stages of post-thymic T-cell differentiation in the rat were most likely to be Thy-1-/RT6+/CD45RC- and Thy-1-/RT6-/CD45RC+ T cells.

Stabilisation of vaccines using trehalose (Q-T4) technology.

Efforts directed towards overcoming the problems of vaccine stability must take cost into consideration. One effective approach is the use of a simple stabilization technology applicable, in principle, to every type of vaccine candidate. Following the lead of Nature, the results in this paper show how such techniques based on trehalose have the potential to transform contemporary vaccine manufacture. The possibilities of novel delivery formats and vaccine combinations, currently not feasible, may now also be realised.

Atherosclerosis and glycation.

Atherosclerosis is the major cause of death in the industrialised world. Though much work on the pathogenesis of atherosclerosis points to 'oxidised' low density lipoprotein (LDL) as a key aetiological feature in the generation of the atherosclerotic plaque, the nature of this 'oxidised' LDL in vivo remains an enigma. We argue here that glycated LDL shows many of the characteristics attributed to 'oxidised LDL' and may be the source of the latter in vivo. These include the increased uptake and impaired degradation of glycated LDL by macrophages and the stimulation of transendothelial chemotaxis of monocytes, cytokine secretion and platelet aggregation. We hypothesise that the covalent binding of glycated LDL to the endothelial cell wall may result in the formation of the early atherosclerotic lesion of the fatty streak and that apolipoprotein E may mediate the physiological clearance of glycated moieties. The proposed role of glycation in the pathogenesis of atherosclerosis would explain its high incidence among diabetics and the contentious epidemiological and experimental correlations between dietary sugar and atherosclerosis.

Extraordinary stability of enzymes dried in trehalose: simplified molecular biology.

We show that extremely fragile biomolecules such as DNA restriction and modifying enzymes can be dried in vitro in the presence of trehalose with no loss of activity, even after prolonged storage. A remarkable and unexpected property of the dried enzyme preparations is their ability to withstand prolonged exposure to temperatures as high as +70 degrees C. This stability is unique to trehalose and is not found with other sugars irrespective of their physical or chemical properties. The immediate significance of these observations is the ability to convert enzymes used in molecular biology into stable reagents. The indefinite stability and high temperature tolerance of these dried enzymes should permit the design of convenient formats that may be of particular significance in the automation of genome mapping and sequencing projects. The stabilization of a wide range of biomolecules by trehalose also has practical implications for a number of areas ranging from basic science, through healthcare and agriculture, to bio-electronics.

In vitro and in vivo effects of monoclonal antibodies against T cell subsets on allogeneic and xenogeneic responses in the rat.

The Syrian hamster-to-rat represents an example of a concordant species difference, and therefore organ transplants using the hamster as the donor and the rat as the recipient are not rejected hyperacutely, as in discordant species combinations. Cellular mechanisms of xenogeneic rejection of hamster hearts by rats were studied both in vitro and in vivo, using monoclonal antibodies to rat T cell antigens. The results of this study reveal that CD4-positive cells of rats proliferated in vitro to both allogeneic stimulators and xenogeneic stimulators from a concordant strain, but required accessory cells of the responder phenotype to proliferate to discordant human stimulators. Monoclonal antibody therapy was used to prevent graft rejection in allogeneic and xenogeneic species combinations, using the rat as the recipient. Treatment with anti-CD4 antibodies was effective in prolonging allograft survival across a full MHC mismatch. No rejection occurred during antibody therapy, and long-term graft survival was achieved in 1/3 of transplanted grafts. The same monoclonal antibody therapy led to increased survival of grafts from hamster donors, but all of these grafts were rejected during therapy, and no long-term graft survival was achieved. Anti-CD8 antibody therapy, combined with anti-CD4 did not improve survival of hamster hearts in rats. Addition of cyclosporine to the anti-CD4 regimen also did not improve graft survival. Injection of an anti-T cell receptor antibody was no better than the anti-CD4 antibody in prolonging the survival times of heart grafts from the concordant xenogeneic species. These data suggest that the rejection of concordant xenogeneic tissue is not wholly a T cell-dependent phenomenon.

Vascular thymus transplantation in rats. Technique, morphology, and function.

A new method of thymus transplantation is introduced, in which the graft is directly connected with the recipient's vascular system. This procedure was used both in euthymic rats and congenitally athymic nude rats. At all tested intervals after transplantation thymus grafts hardly differed from the recipient's own thymus in immunohistology and lymphocyte yield. In athymic nude rats, T cell-dependent immunity, tested by mitogen- and alloantigen-induced T cell responses, as well as by antibody production and delayed-type hypersensitivity after ovalbumin administration, showed that vascular thymus grafts could generate T cell functions to euthymic control levels. We conclude that the technique of vascular thymus transplantation represents a valuable tool, either in fundamental research on thymus function, or for the purpose of immune (re)constitution.

Dry instant blood typing plate for bedside use.

A monoclonal antibody-derived, dry blood grouping plate, based upon the simple disaccharide, trehalose, is described that is indefinitely stable at room temperature and was found to have a 99.8% accuracy when tested against a standard semiautomated assay. This plate can be used by personnel with no specific training to check the recorded A,B,O, and Rhesus blood type of potential transfusion recipients in the field and at the bedside. Trehalose-based reagents may be important for bedside testing and in developing countries where refrigeration is unreliable.

Differences in turnover between thymic medullary dendritic cells and a subset of cortical macrophages.

To investigate the turnover of thymic accessory cells, we performed vascular thymus transplantation in RT7 congenic rats. mAb specific for one of the two allelic variants of the RT7 molecule, as well as mAb specific for either medullary interdigitating cells or a subset of cortical macrophages (M phi), were used on cryostat sections and cell suspensions prepared from grafted thymuses to monitor the turnover of these two cell types. In contrast to the complete turnover of interdigitating cells within 3 wk after transplantation, ED2-labeled cortical M phi showed a very slow turnover. Seventy-six days after transplantation, more than 30% of these M phi were found to be still of donor origin. The different turnover rates of these thymic accessory cells could reflect their function in T cell development.

False-positive signals in enzyme immunoassay (EIA) interactions between rodent IgG subclasses.

Interactions between mouse and rat monoclonal antibodies (MAbs) in EIA have been detected using panels of mouse and rat MAbs of various isotypes. Mouse and rat antibodies of the IgG2a subclass were found to bind to each other most strongly. Immobilised IgG1 antibodies of the two species showed much less interaction. Rat IgG2b and IgG2c were intermediate in binding activity. We were unable to study examples of mouse IgG2b and IgG3 MAbs. By making use of the kappa light chain allotype in the rat we were also able to show intraspecies interactions of rat MAbs with the IgG in rat serum. The molecular basis of these interactions has not been resolved but may involve the extended hinge region and flexible Fab arms of the IgG2a subclass of Ig permitting strong inter domain bonding between the constant region domains of adjacent molecules of this isotype.

RT7-defined alloantigens in rats are part of the leucocyte common antigen family.

Haemopoietic cells carry a variety of cell-surface molecules, some of which are known to have allotypic variation. In rats, the RT7 alloantigenic system has been well documented using alloantisera. We have produced the first mouse hybridoma cell line secreting an antibody, HIS41, which binds to leucocytes of rat strains carrying the RT7.2 but not the RT7.1 determinant. An IgG2b isotype switch variant (HIS41.2b) of the original HIS41 (IgG1 isotype) was also made. HIS41 showed a clear and discrete binding in immunofluorescent and histological experiments and has already been used in several studies on haemopoietic cell turnover and differentiation employing PVG rats congenic for RT7. The present study addresses the question of whether the RT7 gene products are members of the L-CA family, which has been a matter of controversy over the last decade. When using HIS41 for the analysis of tissue distribution and molecular weight of RT7 gene products, a strong similarity was evident with the data reported for the L-CA detected by MRC OX-1 and MRC OX-30. These two MoAb have been reported to bind to all members of the L-CA family. All haemopoietic cells, excluding erythrocytes and the more mature stages of erythropoiesis, stained with HIS41. The molecular weights of HIS41 binding molecules on thymocytes and peripheral T cells were comparable to the L-CA precipitated by MRC OX-1. Capping and sequential immunoprecipitation studies indicated that HIS41 and MRC OX-30-binding molecules were identical. MRC OX-1, however, appeared to bind only a subset of these molecules. Thus, our study confirms the identity of RT7.2 gene products and L-CA. It also revealed a difference between MRC OX-1 and MRC OX-30 not noticed previously.

Inhibition of T cell responses in vitro by an antibody against a novel lymphocyte surface molecule (QCA-1).

We have identified an antigen present on the surface of lymphocytes in the rat which appears to play an important role in the preliminary stages of the immune response. This antigen, which we have called quiescent cell antigen 1 because of its apparent expression only on quiescent cells, is present on the majority of peripheral T and B cells and a small percentage of thymocytes which are located mainly in the medullary region. SDS-PAGE analysis of membrane molecules shows two bands on unreduced gels at approximately 43 and 47 kd. On reduction the bands ran at approximately 46 and 60 kd. When a monoclonal antibody against this antigen (HIS45) is present in an allogeneic mixed leukocyte reaction, it inhibits the proliferation of responding cells completely. When the antibody HIS45 is added to cytotoxic T lymphocyte mediated lysis assays it does not inhibit lysis nor does it affect the specificity of this lysis. Comparison with other antibodies which have been reported to affect lymphocyte function in rats and in other species fail to reveal any which have similar properties.

Rearing rats in a germ-free environment eliminates their odors of individuality.

In order to test the hypothesis that commensal bacteria influence the urinary odors of individuality, we collected urine from PVG and PVG.R1 male rats born by cesarian section and reared in a germ-free environment. Using the habituation-dishabituation test with PVG.RT1 (u) and Lister hooded rats as subjects, we found that urine from the germ-free rats was not discriminated, while urine from conventionally housed rats of the same strains could be discriminated (experiment 1). When the germ-free rats were moved to a conventional animal house after recolonization with commensural flora and their urine collected, it was discriminated, indicating an essential role of bacteria in determining the unique urinary odors of MHC-congenic rats (experiment 2). The conventionally housed and germ-free rats did not differ in the amount of class I antigen in their urine (experiment 3). Finally, urines of PVG and PVG.R1 donors inoculated with a defined and highly restricted flora to render them specific-pathogen-free (SPF) could not be discriminated. Urine from SPF donors moved to a conventional animal house could be discriminated (experiment 4). These results indicate that commensal bacteria are essential for the production of the unique individual odor of the urine of MHC-congenic strains of rats.

Class I and class II regions of the major histocompatibility complex both contribute to individual odors in congenic inbred strains of rats.

The major histocompatibility complex (MHC) of the rat has three regions--A (class I), B/D (class II), and C/E (class I)--and congenic strains are available which differ in each of these regions. We used the habituation-dishabituation procedure to examine the ability of PVG-RT1u male rats to discriminate between the urinary odors of congenic rat strains which differ genetically only at certain individual regions of the MHC. The results of five experiments indicate that discrimination can be made between urine from rats which differ in all three regions of the MHC (PVG vs. PVG-RT1av1 donors), only in the class I A region (PVG vs. PVG.R1 donors), only in the class I C/E region (PVG.R19 vs. PVG-RT1av1 donors), only in the class II B/D region (PVG.R1 vs. PVG.R19 donors), and in all regions except the classical class IA locus (PVG-RT1av1 vs. PVG.R1 donors). These results indicate that all of the MHC regions may contribute to the individual odors of rats.

A monoclonal antibody to a determinant of the rat T cell antigen receptor expressed by a minor subset of T cells.

A hybridoma producing the monoclonal antibody HIS42 was isolated from a fusion between spleen cells from a BALB/c mouse immunized with rat thymocytes and the fusion partner SP2/0. This antibody recognizes a minor subset of T cells in every haplotype of rat tested so far. The subpopulation of HIS42 positive T cells contains both CD4+ and CD8+ cells, in the same ratio as found in the peripheral T cell population. When bound to Sepharose beads, HIS42 induces T cell proliferation in the presence of interleukin-2. In contrast to lymph node T cells, a number of thymocytes were found to express HIS42 only in the cytoplasm or together with membrane expression. Most bright HIS42 surface labelled thymocytes were also positive for MRC OX-44, a marker predominantly identifying mature thymocytes. SDS-PAGE analyses of the membrane molecules immunoprecipitated by HIS42 show two bands on unreduced gels. One of these bands (85 kd) runs as two separate bands at 35 and 48 kd on reduction. The other much weaker broad band (approximately 100 kd) is hardly affected by reduced conditions. Taken together these data suggest that HIS42 is directed against a determinant on the rat T cell receptor for antigen, which is common to a small number of T cells.