Immune suppression genes control the anti-F antigen response in F1 hybrids and recombinant inbred sets of mice

Quantitative genetic analysis of brain copper and zinc in BXD recombinant inbred mice

Copper and zinc are trace nutrients essential for normal brain function, yet an excess of these elements can be toxic. It is important therefore that these metals be closely regulated. We recently conducted a quantitative trait loci (QTL) analysis to identify chromosomal regions in the mouse containing possible regulatory genes. The animals came from 15 strains of the BXD/Ty recombinant inbred (RI) strain panel and the brain regions analyzed were frontal cortex, caudate-putamen, nucleus accumbens and ventral midbrain. Several QTL were identified for copper and/or zinc, most notably on chromosomes 1, 8, 16 and 17. Genetic correlational analysis also revealed associations between these metals and dopamine, cocaine responses, saccharine preference, immune response and seizure susceptibility. Notably, the QTL on chromosome 17 is also associated with seizure susceptibility and contains the histocompatibility H2 complex. This work shows that regulation of zinc and copper is under polygenic influence and is intimately related to CNS function. Future work will reveal genes underlying the QTL and how they interact with other genes and the environment. More importantly, revelation of the genetic underpinnings of copper and zinc brain homeostasis will aid our understanding of neurological diseases that are related to copper and zinc imbalance.

Recessive expression of the H2A-controlled immune response phenotype depends critically on antigen dose

Major histocompatibility complex (MHC) alleles acting as immune response genes are coexpressed in heterozygous individuals and therefore control of immune responses is usually codominant. As an exception to this rule, however, several examples of recessive immune responses have been ascribed to regulatory, e.g. suppressive, interactions. We report here that the recessive phenotype of both antibody and T-cell responses to the mycobacterial 16 000-MW antigen depends critically on a low antigen dose for immunization. On the basis of similar responses in hemi- and heterozygous mice, we suggest that the mechanism of recessive MHC control does not involve regulation by the low-responder allele. We also demonstrated mixed haplotype restriction of peptide recognition for a significant fraction of high-antigen-dose primed T cells. Their paucity under limiting antigen dose conditions may lead to the recessive expression of MHC control. In conclusion, our results suggest that recessive MHC control can be explained as a simple gene dosage effect under conditions where antigen is limiting, without a need for regulatory mechanisms.

Natural variation in immune responsiveness, with special reference to immunodeficiency and promoter polymorphism in class II MHC genes

This review deals with natural selection operating on heterozygotes as a key factor controlling (a) the frequency of immunodeficiencies, and (b) promoter polymorphism in MHC class II genes. The known difference in frequency distribution of X-linked and autosomal deficiencies lend support to this possibility, and suggest that the frequency of neonatal defect may rise as old-established equlibria between entry and exit of deleterious mutations change. MHC class II gene promoters differ in their capacity to favor Th1 (or reciprocally Th2) responses, thus suggesting that promoter polymorphism is sustained by the greater flexibility in response that this confers on heterozygotes.

Tetrahymena gene encodes a protein that is homologous with the liver-specific F-antigen and associated with membranes of the Golgi apparatus and transport vesicles

The F-antigen is a prominent liver protein which has been extensively used in studies on natural and induced immunological tolerance. However, its intracellular localization and biological function have remained elusive. It has generally been assumed that the F-antigen is confined phylogenetically to vertebrates. Now we have cloned and characterized a gene from the ciliated protozoan Tetrahymena thermophila encoding a protein which clearly is homologous with the rat F-antigen. The coding region of the Tetrahymena F-antigen (TF-ag) gene specifies a 46,051 M(r) protein and is interrupted by three introns. In accordance with the predicted molecular mass of the TF-ag protein, antibodies raised against a cro-lacZ'-TF-ag fusion protein specifically recognized a 45,000 M(r) protein in Western blots of total T. thermophila protein. Immunoelectron microscopy demonstrated that the TF-ag is associated with membranes of the Golgi apparatus and transport vesicles pointing to a role of TF-ag in membrane trafficking. Transcription of the TF-ag gene, as determined by run-on analyses, was only detectable in growing cells, and following transfer to starvation condition pre-existing TF-ag mRNA was rapidly degraded. The abundance of the TF-ag protein, however, declined only moderately during prolonged periods of starvation demonstrating that extensive release of the TF-ag did not take place. In combination these results suggest that the TF-ag protein is a recycled constituent of the intracellular membrane network in T. thermophila.

The influence of I-E on the generation of autoantibody and specific suppression in rat erythrocyte-immunized mice

A proportion of the antibodies produced by mice in response to the injection of rat erythrocytes (RRBC) cross-react with autologous red cells. When spleen cells from mice so immunized are transferred to naive syngeneic recipients, the recipient mice produce high anti-RRBC antibody titres but little or no autoantibody. This phenomenon has been attributed to the action of suppressor T cells. To date, the only mouse strain which consistently fails to demonstrate specific suppression of the autoantibody response is the SJL, which lacks the I-E molecules suggested to be important in the generation of suppressor T cells. The results presented here show that some, but not all, I-E negative strains of mice are capable of exhibiting transferable suppression of RRBC-induced antibodies.

The identification and cloning of the murine genes encoding the liver specific F alloantigens

The liver specific F alloantigen is a highly conserved abundant protein found in hepatic cytoplasm; smaller amounts are detected in renal tubule cells and the perikaryon cells of the central nervous system. Although the biological function of the F alloantigen is unknown, the immune response to F has been extensively studied as a murine model of tolerance and autoimmunity. Murine F exists in two allelic forms, designated F type 1 and type 2, each of approximately 43 kDa. The immune response to the allotypic form is restricted to mouse strains of I-Ak. Responding strains immunized with allotypic F break tolerance and produce precipitating antibody that reacts with both allelic forms, i.e., immunogen and self. Thus an autoantibody is produced. Using the previously isolated rat F cDNA as a probe, we report the cloning and sequencing of the two murine F allotypes. These two alleles are nearly homologous except at the extremes of the coding sequence. There are a number of regions within the F sequence that are similar to peptides that interact specifically with I-Ak. In particular, there is a sequence near the carboxy terminus, where the two allotypes differ, that has homology to the I-Ak restricted malarial antigen peptide of the ring-infected erythrocyte surface antigen (RESA).

Sequences of the mouse F protein alleles and identification of a T cell epitope

F protein is found predominantly in the liver and is of unknown function. The protein has been of interest to immunologists in the areas of self tolerance and the immunogenetics of the anti-F protein response. In the mouse there are two alleles (F1 and F2), and although mice are completely tolerant to the self form of the protein, mice of responder strains make a good antibody response to immunization with the non-self form. This response cross-reacts with the self form, implying firstly, that autoreactive B cells are present and that tolerance is therefore maintained at the T cell level, and secondly, that the difference between the two allelic products defines a T cell epitope. Primers based on the published sequence for rat F protein were used in the polymerase chain reaction to amplify the cDNA for the two mouse alleles. Subsequent sequencing shows a high degree of sequence identity between the rat and mouse cDNA. The two mouse cDNA are identical apart from a single A to G base change which predicts an asparagine (F1 protein) to aspartate (F2 protein) amino acid residue change. Using allele-specific oligonucleotide probes we confirmed that this base change has the same strain distribution as the previously determined F protein type. Isoelectric focusing shows that F1 protein migrates in a more basic position than F2 protein, as predicted by the asparagine to aspartate change. Finally, a synthetic peptide from the allovariable site of F2 protein will successfully restimulate T cells in vitro from an F1 type mouse primed in vivo with whole F2 protein, whereas the corresponding peptide from F1 protein will not. This is evidence that, as predicted, the allovariable site does indeed define a T cell epitope. Peptides covering the rest of the F2 protein molecule were not stimulatory.

Selection of anti-F protein B-cell repertoires in normal mice

The hypothesis that self-tolerance to F protein antigen exclusively concerns T cells was tested by determining the frequencies of B lymphocytes producing anti-F antibodies in bone marrow (BM), spleen and peritoneal exudate (PEC) cells from normal, immune or tolerant animals, and in responder and non-responder mouse strains. Using an ELISA spot assay and lipopolysaccharide stimulation, we found that anti-F frequencies were highest in BM and "naturally activated" large spleen cells, followed by resting spleen and PEC cells. Anti-F specificities were also induced among "natural" Ig-secreting cells of normal individuals. Specific immunization of responder mice doubled the splenic frequencies, while tolerization had no effect. Similar results were obtained in BALB/c and A/J mice, while C57BL/6 contained fewer anti-F B cells in spleen, but not in BM. These results support the notion that self-tolerance to F antigen can primarily be ascribed to T cells, but they also show F-antigen-specific selection of B-cell repertoires.

Dominant reduced responsiveness controlled by H-2(Kb)Ab. A new pattern evoked by Thy-1 antigen and F liver antigen

In the most frequently used panel of H-2 recombinant strains, B10.A, B10.A(4R), B10.A(5R), and B10, inhibition of the immune response has hitherto mapped to H-2E. Inhibition of the responses to Thy-1 antigen and to F liver protein, as described here, maps in a novel pattern to H-2KbAb, and presumably to H-2Ab. Enhancement of the adoptively transferred anti-Thy-1 response by treatment with CD8-specific antibody suggests, very provisionally, that T cells with suppressive activity mediate the inhibition. The evolution of this new pattern, and of dominant reduced responsiveness in general, is discussed and its relevance to immunological diseases assessed. An enzyme-linked immunosorbent assay (ELISA) for F-specific antibodies is introduced.

The structural gene for F liver protein (Flp) maps to chromosome 5 of the mouse

The BXD and AKXL panels of recombinant inbred mouse strains have been typed for the F liver protein alloantigen. The structural gene for F liver protein gene (Flp) is placed on the distal part of chromosome 5, between the known markers Bcd-1 and Gus-s. This excludes the possibility that F liver protein is a major histocompatibility complex molecule, and in turn raises a question about the uniqueness of F and certain other proteins as purgers of self-reactivity among T but not B cells. The typed RI strains have then been used for the immunogenetic studies presented in the succeeding article.