Strain influences on inflammatory pathway activation, cell infiltration and complement cascade after traumatic brain injury in the rat.

Increasing evidence suggests that genetic background affects outcome of traumatic brain injuries (TBI). Still, there is limited detailed knowledge on what pathways/processes are affected by genetic heterogeneity. The inbred rat strains DA and PVG differ in neuronal survival following TBI. We here carried out global expressional profiling to identify differentially regulated pathways governing the response to an experimental controlled brain contusion injury. One of the most differentially regulated molecular networks concerned immune cell trafficking. Subsequent characterization of the involved cells using flow cytometry demonstrated greater infiltration of neutrophils and monocytes, as well as a higher degree of microglia activation in DA compared to PVG rats. In addition, DA rats displayed a higher number of NK cells and a higher ratio of CD161bright compared to CD161dim NK cells. Local expression of complement pathway molecules such as C1 and C3 was higher in DA and both the key complement component C3 and membrane-attack complex (MAC) could be demonstrated on axons and nerve cells. A stronger activation of the complement system in DA was associated with higher cerebrospinal fluid levels of neurofilament-light, a biomarker for nerve/axonal injury. In summary, we demonstrate substantial differences between DA and PVG rats in activation of inflammatory pathways; in particular, immune cell influx and complement activation associated with neuronal/axonal injury after TBI. These findings suggest genetic influences acting on inflammatory activation to be of importance in TBI and motivate further efforts using experimental forward genetics to identify genes/pathways that affect outcome.

Generation of T cells with lytic specificity for atypical antigens. III. Priming F1 animals with antigen-bearing cells also having reactivity for host alloantigens allows for potent lytic T cell responses.

Here, we explore the conditions required for generating two different highly potent F1 antiparental killer cell populations to unusual antigens in rats. The first, L/DA anti-DA, has lytic specificity for two antigen systems: MTA, a mitochondrial antigen expressed on DA and DA Lewis (L) target cells restricted by RT1A class I molecules; and H, an antigen that maps to the class I-like RT1C region and is present only on parental target cells from donors homozygous at the major histocompatibility complex. The second killer population is generated in the reciprocal DA/L anti-DA combination and has lytic specificity only for the H antigen system. We show that the killer cells are T cells, and that generation of these F1 cytotoxic T lymphocytes (CTL) requires an in vivo priming step in which it is essential that the inoculated parental cells bear the relevant target antigens and possess alloreactivity for F1 host antigens. The requirement for alloreactivity and antigen on the same priming cell population suggests that these potent lytic responses depend on a situation akin to a hapten-carrier effect that bypasses otherwise ineffective helper responses by the host to these unusual antigens. Restimulation of F1 lymphocytes in culture is also necessary, requiring the presence of antigen on irradiated lymphoblast stimulator cells, but alloreactivity to responder cell antigens is not necessary; normal, nonactivated lymph node cells are completely ineffective as stimulators. For effective lysis, the target cells need not possess the potential for alloreactivity to responder F1 CTL. We also demonstrate in a preliminary way additional antigen systems defined by killer populations raised with other F1 antiparental strain combinations.

Generation of T cells with lytic specificity for atypical antigens. II. A novel antigen system in the rat dependent on homozygous expression of major histocompatibility complex genes of the class I-like RT1C region.

Lymphocytes from parental strain DA rats can induce potent killer cell responses to atypical antigen systems in F1 Lewis (L)/DA and DA/L recipients. Here, we describe an antigen system, H, present on homozygous parental target cells, but not on F1 cells. This antigen system is unusual in several respects: it does not involve class I RT1A gene products usually used by killer cell responses in the rat, it maps to the major histocompatibility complex (MHC) class I-like RT1C region, and it requires homozygous expression of RT1Cav1 alleles. This may be another example, this time involving the RT1C region, of an MHC gene product antigenically altered by an MHC-linked trans-activating modifier gene.

Recognition of histocompatibility determinants controls reactivity of auto-sensitized lymphocytes against neural tissues.

Thoracic duct lymphocytes from rats sensitized against syngeneic spinal cord rapidly produce damage in cultures of syngeneic cerebellar cells but coexist indefintely with allogeneic cultures. Lymphocytes from donors that have been sensitized against allogeneic spinal cord attack cultures of syngeneic and specific allogeneic cerebellum but not cells from rats of a third, unrelated strain.

Immunological properties of subcellular rat lymphocyte preparations. Primary allogeneic stimulation in vitro by fractions containing Ia (RT1-B), but not RT1-A antigens.

Rat thymocyte membrane fractions have been prepared which exhibit strain-specific primary mixed-lymphocyte reaction (MLR)-stimulating and Ia (RT1-B) antigenic properties. These preparations lack the antigenicity of classical, serologically-defined RT1-A (Ag-B) antigens, as defined by in vitro serologic assays. Furthermore, after immunization of allogeneic hosts, specific anti-Ia and MLR-blocking antibodies, but not anti-AgB, alloantibodies are elaborated. Thymidine suicide experiments show that the same clones respond to whole cells and the fragments made from those cells, and the response segregates appropriately in F2 progeny as a major histocompatibility complex (RT1)-linked phenomenon. Hence, it is possible to generate Ia-related allogeneic helper signals in primary, as well as secondary, in vitro responses, using subcellular membrane fragments that have restricted expression of RT1-B-, but not RT1-A-, encoded antigens.

Occurrence of a theta-like antigen in rats.

A rat antigen system parallel to the mouse theta system has been described(*) All rat strains tested expressed an antigen cross-reactive with the theta-AKR specificity of mice while none cross-reacted strongly with theta-C3H. The rat antigen may be demonstrated by either absorption or direct complement-mediated killing of rat thymocytes. Patterns of organ distribution and developmental appearance in the nervous system of rats also parallel those previously reported for theta in mice.

Binding of purified, soluble major histocompatibility complex polypeptide chains onto isolated T-cell receptors. I. Reactivity against allo- and self-determinants.

In this study, we tried to get information about the fine antigen-binding ability of purified, soluble, idiotype-positive T-cell receptor molecules. Lewis anti-DA T-cell receptors were purified from normal Lewis serum by the use of anti-idiotypic immunosorbent and sodium dodecyl sulfate-polyacrylamide gel, and were coupled to cyanogen bromide-activated Sepharose 4B. In parallel, Lewis anti-DA, Lewis anti-BN, and DA anti-Lewis alloantibody immunosorbents were prepared. The major Ag-B chain (44,000 daltons) and the two polypeptide chains (34,000 and 27,000 daltons) of Ia were purified from Lewis, DA, and BN lymphocytes and absorbent on the above-mentioned immunosorbents. We found that the major Ag-B chain as well as the two Ia chains were bound to the alloantibody columns if they were derived from the corresponding allogeneic strain. No retaining ability for self-major histocompatibility complex (MHC) or third-party MHC chains was noted with the alloantibody immunosorbents. When using immunosorbents made up of idiotypic T-cell receptors, only two MHC polypeptides of the relevant allo-MHC type were retained, namely, the Ag-B and the heavy Ia chains. No detectable activity was observed when testing the same column for reactivity against third-party MHC polypeptide chains. However, the Lewis anti-DA T-cell receptors could be shown to display weak, but significant, reactivity toward one Lewis MHC polypeptide chain, that is, the heavy chain of Ia type.

Differences in the repertoire of the Lewis rat T cell response to self and non-self myelin basic proteins.

We have examined the fine specificity of a panel of cloned T cell hybridomas generated from Lewis rats immunized with guinea pig (GP) or Lewis rat myelin basic protein (MBP) to determine the autoimmune T cell repertoire that develops in experimental allergic encephalomyelitis (EAE). This analysis has demonstrated that GP MBP, which was approximately 10-fold more potent for EAE induction than the autologous rat MBP, produced a population in which almost one-fourth of the members responded to GP-unique determinants and displayed no crossreactivity on the self antigen. The remaining majority of GP MBP-induced clones were specific for the 68-88 encephalitogenic determinant and could be subdivided into three groups based on their varying responses to the 68-88 peptide and rat and rabbit MBPs. Surprisingly, one of these groups showed equal reactivity to GP and rat MBPs. In contrast, the clonotype composition of the T cell population induced by rat MBP was quite different. One-half of these clones comprised a single group responding to the 68-88 determinant, reacting equally with GP and rat MBP. All of these responded to the same range of antigen concentrations as their GP-induced counterparts. The remaining half of that population contained a collection of clones that was nearly as encephalitogenic as the 68-88 population after propagation as a short-term T cell line. These clones were specific for at least three distinct antigenic determinants, all displaying extensive cross-species reactivity, and required as little or less rat MBP for maximal stimulation as did the 68-88-reactive clones. We therefore conclude that the T cell repertoire for MBP does include clones with reactivity to both 68-88 and non-68-88 determinants of GP and rat MBPs, and that both MBPs appear to be equally capable of stimulating these clones in vitro. However, the differences in the clonotype composition of the populations induced by immunization with these two antigens suggest that rat and GP MBPs are subject to different immunoregulatory constraints in the animal and may account for the difference in the encephalitogenic potential of these two antigens.

A monoclonal antibody to a constant determinant of the rat T cell antigen receptor that induces T cell activation. Differential reactivity with subsets of immature and mature T lymphocytes.

mAb R73 detects a T cell-specific surface molecule consisting of two disulfide-linked subunits of 40 and 46 kD, respectively, on 97% of peripheral rat T cells, as defined by the OX-52 marker. Of the few OX-52+ R73- cells, none are CD4+ but many express the CD8 antigen known to be present on rat NK cells. mAb R73 is mitogenic for unseparated spleen cells and for purified T cells. In the absence of non-T "accessory cells", stimulation by R73 requires artificial crosslinking of the mAb and is largely dependent on exogenous IL-2. Overnight incubation of purified T cells with crosslinked R73 mAb induces blastoid transformation, IL-2-R expression, and modulation of the R73 antigen. In the rat thymus, mature medullary cells express the R73 determinant at the same level as peripheral T cells, whereas 94% of CD4-CD8- thymocytes are R73-. The major CD4+8+ thymocyte population contains 25% R73- and 70% R73low cells. Thymocytes of the CD4-CD8+OX-44- subpopulation that are the direct precursors of CD4+CD8+ cells display a continuum of R73 antigen density from undetectable to very low levels. We conclude that R73 is most likely directed at a constant determinant of the rat alpha/beta heterodimeric TCR and suggest that CD8+ immature thymocytes are the first cells in the T cell differentiation pathway to express this molecule at their surface.

A nephritogenic rat monoclonal antibody to mouse aminopeptidase A. Induction of massive albuminuria after a single intravenous injection.

Antibodies directed against antigens present on renal epithelial cells can cause membranous glomerulonephritis in experimental animals, which closely resembles the human form of this disease. However, most antibodies produced so far fail to cause the persistent and severe proteinuria that is seen in humans. In our search for new antibodies of this kind, we have now produced a monoclonal antibody (mAb) against mouse aminopeptidase A, a hydrolase that is present in the mouse kidney. The mAb (ASD-4) was prepared by fusion of mouse myeloma cells with splenocytes of Lou rats immunized with brush border (BB) membranes from mouse kidneys. ASD-4 is of the IgG1 subclass and reacts with a 140-kD protein as demonstrated by immunoprecipitation on radiolabeled BB membranes. In indirect immunofluorescence and immunoelectronmicroscopy of normal mouse kidneys, ASD-4 was diffusely present on the BB of the S1 and S2 segments of the proximal tubules, and on the cell membranes of the glomerular visceral epithelia. It also bound to cell membranes of nonglomerular endothelia, smooth muscle cells of arteries, and juxtaglomerular cells. After injection of ASD-4 into normal mice, an immediate homogeneous binding to the capillary wall was seen that gradually changed into a fine granular pattern after 1 d. This glomerular binding was followed by binding to the BB and basolateral membranes of the convoluted proximal tubules. Immediately after injection of ASD-4, a dose-dependent albuminuria occurred that lasted for at least 16 d. ASD-4 is thus a new rat mAb against a well-defined renal epithelial antigen that causes not only membranous glomerulonephritis after a single injection in the mouse, but also severe albuminuria.

Comparative effects of stressors on behavioral and neuroimmune responses of fawn-hooded (FH/Wjd) and Wistar rats: Implications for models of depression.

Patients with depression and rodent models of depression show increased cytokines and activated microglia. Fawn Hooded (FH/Wjd) rats have long been used as a model of depression based on their depressive-like behaviors, high basal corticosterone levels and altered serotonergic levels, but little is known about the neuroimmune function in this model. To test whether depressive-like behaviors relate to dysfunction of the neuroimmune system, depressive-like behaviors in the forced swim test (FST) and corticosterone (CORT) response to the swim test were compared in male Fawn Hooded versus Wistar rats, and cytokine levels in plasma and brain and plasma CORT in response to lipopolysaccharide (LPS, an endotoxin that activates the neuroimmune system) or 1 h restraint were measured. Fawn Hooded rats had more depressive-like behaviors in the FST (decreased swim time and increased immobility) and increased overall plasma CORT compared with Wistar rats. Additionally, Fawn Hooded rats exhibited blunted brain and plasma cytokine response to LPS compared with Wistar rats, an effect that might be related to the blunted plasma CORT response to LPS. No strain differences were found on these measures in response to restraint stress. These results suggest that Fawn Hooded rats have a depressive-like phenotype potentially more closely associated with serotonin dysregulation and a dysregulated HPA axis and remain a relevant model for further defining the role of these systems in depressive conditions.

Immunological characteristics of Hatano high-and low-avoidance rats.

Hatano high- and low-avoidance (HAA and LAA) rats have been genetically selected on the basis of their two-way active avoidance behavior, and have been shown to differ in other behavioral and hormonal parameters. Since close interconnections among the nervous, endocrine and immune systems have been well documented, these two strains might possess differences in aspects of immunological action. In Experiment 1, plasma levels of IgG, IgM, complement 3 (C3), classical pathway hemolytic complement (CH50) and beta(2)-microglobulin were compared between males of the two strains at 5 and 24 weeks of age. Plasma levels of IgG and CH50 were lower in LAA than HAA rats at 5 weeks of age, whereas those differences disappeared at 24 weeks of age. There were no differences between the two strains in plasma levels of IgM, C3 and beta(2)-microglobulin. In Experiment 2, antibody production to sheep red blood cells (SRBC) and mitogen-induced lymphocyte proliferation were compared between 12-week-old males of the two strains. Antibody responses in the PFC assay, plasma anti-SRBC-IgM levels and spleen weights were higher in LAA than HAA rats. LPS-induced lymphocyte proliferation was greater in LAA than HAA rats. It was concluded that HAA rats show earlier development of immunological development, but that antibody production and mitotic response of B lymphocytes may be more pronounced in adult LAA than HAA rats. The strain differences observed in the immunological response may indicate the usefulness of using Hatano rats in studies of behavioral-immunological relationships.

Autoimmune destruction of islets transplanted into RT6-depleted diabetes-resistant BB/Wor rats.

We report a novel animal model of islet transplantation that distinguishes recurrence of autoimmunity from allograft rejection. In this study, diabetes-resistant (DR) BB rats, less than 1% of which develop spontaneous diabetes, were made hyperglycemic by either a single injection of streptozocin (STZ) or in vivo immune elimination of a regulatory T-lymphocyte subset that expresses the RT6 alloantigen. DR islet grafts were then transplanted into both groups. DR transplants into STZ-induced diabetic DR rats produced long-term normoglycemia. In contrast, DR transplants into DR rats that had been treated with anti-RT6 monoclonal antibody were all destroyed within an average of 4 days. Allogeneic islets transplanted into both STZ-induced and RT6-depleted diabetic DR rats were rejected within a mean of 3 days. We conclude that failure of DR islet grafts in RT6-depleted diabetic DR BB rats represents recurrent autoimmunity.

Differences in humoral insulin-antibody response among inbred Lou/M rats and epitope presentation differences in ELISA and radioimmune titration.

Insulin antibodies were not detected in an insulin-capture enzyme-linked immunosorbent assay (ELISA), but they were easily detected in an insulin-copolymer-capture ELISA. Thus, there is a high degree of steric hindrance because of the proximity of the epitopes on the insulin monomer. This is circumvented by substituting an insulin copolymer for insulin in the capture ELISA. A regression analysis comparing the titers of 28 Lou/M rat insulin antiserums measured by liquid-phase radioimmune titration (RIT) with titers obtained in the direct insulin ELISA was not significant (P greater than .05). Thus, epitopes on insulin available and/or masked for antibody binding in the RIT differ from those available and/or masked in the direct insulin ELISA. As more of the epitopes become available when an insulin copolymer is substituted for monomeric insulin in the ELISAs, a significant positive correlation (P less than .05) with the RIT was observed with these 28 insulin antiserums. Twenty-five percent (7 of 28) of these antiserums contained more antibodies that bound to epitopes available in the ELISAs that were masked in the RIT. Conversely, two antiserums contained more antibodies that bound to epitopes that were available in the RIT but were masked in the ELISAs. Thus, the amount of insulin antibodies measured in a given antiserum can vary substantially, depending on which epitopes are made available or are masked in the particular antibody-titration method used. These results demonstrate that the humoral immune response to insulin among inbred Lou/M rats can vary in insulin-antibody levels as well as the epitopes on insulin to which the antibodies bind.

Prevention of diabetes in BB rats. I. Evidence suggesting a requirement for mature T cells in bone marrow inoculum of neonatally injected rats.

Injection of major histocompatibility complex (MHC)-compatible bone marrow cells from normal animals into neonatal BB rats resulted in a striking decrease in incidence of diabetes and restoration of concanavalin A (ConA) and mixed lymphocyte responses. However, injection of bone marrow cells pretreated with anti-rat thymocyte antiserum plus complement to remove mature T cells had no effect on incidence of disease, suggesting that mature T cells in the bone marrow inoculum were responsible for prevention of diabetes. Because the decreased incidence of diabetes in rats injected with untreated bone marrow appeared to be unrelated to the extent of lymphopenia in these animals, the involvement of T cells in the onset of diabetes must reflect a defect in the normal function of these cells rather than their absolute number. Approximately 50% of the W3/13+ cells in the spleens of BB rats lacked the OX-8 and W3/25 T cell subset markers. The identity of this W3/13+, OX-8-, W3/25- blank subset remains to be established. Our results, interpreted in light of studies from the other laboratories, suggest the existence of multiple abnormalities in the BB rat, including the presence of T cells as effector or helper cells that augment onset of disease and the absence of a regulatory T cell circuit that could prevent the disease.

Macrophage-mediated islet cell cytotoxicity in BB rats.

Islet cell killing mediated by natural killer cells and T-lymphocytes in diabetes-prone (DP) and diabetic BB rats has been described, but other killing mechanisms may also be involved. Histopathologic studies suggest that macrophages are the first immune cells to infiltrate islets. To determine if macrophages are the first cells mediating islet damage, macrophage-mediated cytotoxicity was evaluated in BB rats of different ages. Splenic macrophages isolated from DP rats at 33, 100, 120, and 140 days of age showed no enhanced islet killing compared with diabetes-resistant rats. Killing at diabetes onset (121 +/- 14 days) was markedly increased (43 +/- 9.3%) compared with age-matched diabetes-resistant controls (19 +/- 8.3%, P less than .001). Islet inflammation was monitored at all time points. At 120 and 140 days of age, 9 of 11 (82%) DP rats had insulitis, and cytotoxicity was increased in 6 of 11 (55%) rats, which is similar to the number of DP rats that progress to diabetes. At 100 days, 3 of 6 (50%) DP rats again showed diabetic levels of killing, even in the absence of insulitis. These data indicate that 1) islet inflammation is dissociated from clinical diabetes onset, 2) splenic macrophages may have islet-killing potential before islet inflammation, 3) macrophage-mediated islet killing is elevated in all animals immediately after diabetes onset, and 4) macrophages, in addition to natural killer cells and T-lymphocytes, are responsible for cell-mediated islet destruction and thus are candidates for the first cellular effector to result in islet killing.

Unaltered class II histocompatibility antigens and pathogenesis of IDDM in BB rats.

The BB rat spontaneously develops insulin-dependent diabetes mellitus (IDDM) as an autoimmune abnormality involving the class II molecules of the major histocompatibility complex (MHC). The rat MHC (RT1 complex) encodes two class II loci, RT1.B and RT1.D. The possibility that variant or unique class II MHC molecules may be associated with IDDM susceptibility was directly examined by determining the nucleotide sequences of class II mRNAs and/or cDNAs from the diabetes-prone (DP) BB rat, the diabetes-resistant (DR) BB rat, the normal histocompatible Wistar-Furth (WF) rat, and the Lewis rat. Sequence analysis indicates that the beta-chains of the RT1.B and RT1.D molecules of the u haplotype from DP-BB, DR-BB, and WF rats are identical but that they are different from other rat alleles and published mouse class II sequences. At the nucleotide level, the NH2-terminal domain of RT1.D beta of the BB and WF rats differs by a single silent nucleotide substitution. Comparisons with the sequences of the Lewis rat indicate hypervariable allelic differences and that the u and I haplotypes are remarkably similar. These findings establish that the class II molecules of the DP-BB rat are not variant or unique and that unaltered class II molecules of the u haplotype support the autoimmune response in the BB rat.

Gastric parietal cell and other autoantibodies in the BB rat.

A longitudinal study of circulating autoantibodies in the sera of 48 BB rats was performed by indirect immunofluorescence. No pancreatic islet cell, adrenocortical, or thyroid microsomal autoantibodies were found. However, autoantibodies reactive to gastric parietal cells (PCA), smooth muscle, and thyroid colloidal antigens were identified, PCA were not detected in Wistar-Furth or BB x Wistar-Furth F1 hybrid rats. The range of ages at the time of first appearance of PCA was the same as that of onset of insulin-dependent diabetes (IDD) in the BB rats, suggesting that the processes leading to PCA and IDD were occurring at the same time of life in these animals. The presence of PCA was associated with degrees of lymphocytic gastritis and with squamous metaplasia of the gastric mucosa in the oldest BB rats (9 mo of age). Levels of serum iron and vitamin B12 did not differ between PCA-positive and PCA-negative BB rats, nor was achiorhydria found in any rat studied. The identification of PCA (and chronic gastritis) and other autoantibodies in the BB rat suggests that these animals have an underlying autoimmune diathesis. These findings thus provide indirect support for an autoimmune pathogenesis for IDD in the BB rat.

Lack of systematically found insulin autoantibodies in spontaneously diabetic BB rats.

Insulin autoantibodies (IAAs) occur in newly diagnosed human insulin-dependent diabetes mellitus (IDDM) patients, but their presence in BB rats is controversial, possibly due to assay differences or variability in the animals studied. To resolve this controversy, IAAs were measured in well-characterized inbred BB rats both in radioligand assays with 125I-labeled rat insulin I or II, respectively, and in an enzyme-linked immunosorbent assay (ELISA) with rat insulin as antigen. In prospective studies, a total of 57 serums from 16 diabetes-prone (DP) BB rats were obtained during an interval ranging from 15 wk to the last week before onset and at onset of diabetes. At comparable ages, 21 serums were obtained from 8 DP BB rats not developing diabetes, and 70 matched serums were obtained from 19 diabetes-resistant (DR) BB rats. Levels of antibody binding increased slightly with increasing age in DP and matched DR rats. Two rats were positive at onset of IDDM in all assays but not in earlier samples. Otherwise, only few isolated serums from both types of rats regardless of diabetes had increased binding in one of the assays. In a cross-sectional study, the insulin-binding levels in 150-day-old DP rats (n = 20) that had not yet developed diabetes did not correlate with insulitis present in 3 of 20 rats and did not differ from 150-day-old DR BB rats (n = 20).(ABSTRACT TRUNCATED AT 250 WORDS)

Elevated mRNA levels of major histocompatibility complex class II genes in lymphocytes of autoimmune BB rats.

The BB rat spontaneously develops autoimmune abnormalities such as insulin-dependent diabetes mellitus and thyroiditis. The autoimmunity of the BB rat is controlled in part by genes of the major histocompatibility complex (MHC), known as the RT1 complex in the rat, and accumulating evidence suggests the involvement of MHC class II molecules. The RT1 complex specifies two types of class II molecules, which are encoded by the loci RT1.B and RT1.D. We have determined the relative steady-state mRNA levels of the class II genes RT1.B beta, RT1.D alpha, and RT1.D beta in splenic lymphocytes from individual autoimmune BB rats of various ages and from age-matched histocompatible normal Wistar-Furth (WF) rats. The relative steady-state mRNA levels of the RT1.D alpha and RT1.D beta genes, but not of the RT1.B beta gene, were elevated approximately 2.5-fold in lymphocytes of prediabetic BB rats 45-75 days old in comparison with age-matched normal WF rats and older BB rats greater than 75 days old. In the diabetic and nondiabetic BB rats greater than 75 days old, the RT1.D alpha and RT1.D beta transcripts were found at lower normal levels, similar to that of WF rats. In contrast, the RT1.B beta transcripts were found at comparable levels in lymphocytes of the BB and WF rats at all ages examined. The increased steady-state mRNA levels of the RT1.D alpha and RT1.D beta genes in the prediabetic BB rats may reflect differences in the proportion of lymphocytes expressing these genes and thus differences in splenic lymphocyte populations.(ABSTRACT TRUNCATED AT 250 WORDS)