Broad programming by IL-2 receptor signaling for extended growth to multiple cytokines and functional maturation of antigen-activated T cells.

Coincident production of IL-2 and induction of high-affinity IL-2R upon TCR engagement has precluded a clear distinction for the biological outcome of signaling through TCR/costimulatory molecules vs the IL-2R. Using a novel transgenic mouse on the IL-2Rbeta(-/-) genetic background, this study has separated the relative outcome of signaling through the TCR and IL-2R. We show that stimulation through the TCR and CD28 or CD40 ligand directly leads to T cell activation and several rounds of proliferation in an IL-2-independent fashion. However, this stimulation is insufficient for extended T cell growth to multiple cytokines or differentiation into CTL or IFN-gamma-secreting effector T cells. IL-2 is required for these functions in part by regulation of cyclin D3 and granzyme B. Somewhat less efficiently, IL-4 stimulation of these transgenic T cells redundantly rescued many of these activities. These data demonstrate a fundamental requirement for IL-2 and perhaps other common gamma-chain-dependent cytokines to promote selective gene expression by Ag-activated T cells for their subsequent growth and differentiation into effector T lymphocytes.

Control of T cell development in vivo by subdomains within the IL-7 receptor alpha-chain cytoplasmic tail.

IL-7/IL-7R signaling functions in both growth and differentiation during T cell development. In this study, we examined the extent these activities were controlled by signaling associated with distinct IL-7R alpha cytoplasmic domains by transgenic expression of wild-type or cytoplasmic deletion mutants of IL-7R alpha in the thymi of IL-7R alpha(-/-) mice. We show an essential requirement for the tyrosine-containing carboxyl-terminal T domain in restoring thymic cellularity, pro-/pre-T cell progression, and survival. In contrast, the functional differentiation of TCR alpha beta cells and the development of TCR gamma delta cells are partially independent of the T domain. Thus, separate cytoplasmic domains of the IL-7R alpha chain differentially control distinct functions during T cell development, whereas normal IL-7R-dependent thymic development requires the integrated activity of all these domains.

Normal lymphoid homeostasis and lack of lethal autoimmunity in mice containing mature T cells with severely impaired IL-2 receptors.

The importance of IL-2Rbeta function for immune regulation is highlighted by the severe impairment in lymphoid cell function in IL-2Rbeta-deficient mice. It has been speculated that failed IL-2/IL-2R signaling in peripheral T cells causes the associated autoimmunity, imbalanced peripheral lymphoid homeostasis, and defective T cell function. This study explored the requirement for IL-2Rbeta function in mature T lymphocytes. We show that transgenic thymic expression of the IL-2R beta-chain in IL-2Rbeta-deficient mice prevents lethal autoimmunity, restores normal production of B lymphocytes, and results in a peripheral T cell compartment that is responsive to triggering through the TCR, but not the IL-2R. The dysfunction of the IL-2R is illustrated by the near complete failure of mature T cells to proliferate to IL-2 in vitro and in vivo, to differentiate into CTL, and to up-regulate IL-2Ralpha expression. These data indicate that lymphoid homeostasis is largely maintained despite a nonfunctional IL-2R in mature T lymphocytes and suggest that IL-2Rbeta provides an essential signal during thymic development to regulate self-reactivity.

APOE is linked to Alzheimer's disease in a large pedigree.

Although previous association studies have demonstrated that the APOE4 allele is a risk factor for Alzheimer's disease (AD), its value for the prediction of AD in individuals is <100%. The limited predictive value of epsilon4 is also seen in multiply affected families where the epsilon4 allele is not tightly linked to AD. We analyzed a large pedigree multiply affected with AD by lod score linkage analysis at the known loci associated with AD. In this pedigree, the APOE/APOCI gene area was linked to the development of AD, while no linkage was detected to any of the other loci known to be associated with the disease. In this family, then, the inheritance of an epsilon4 allele is highly associated with the early development of the disease (mean age of onset, 62 years), and is a good predictor of disease. However, given the wealth of evidence for association, but not linkage, of APOE4 to AD, we believe this finding suggests that another factor (or factors) interact(s) with APOE to precipitate early disease, and produce positive linkage results. The nature of this factor presently remains unknown.

No interaction between the APOE and the alpha-1-antichymotrypsin genes on risk for Alzheimer's disease.

It is now known that possession of one of the three common forms of the apolipoprotein E gene (allele epsilon 4) confers an increased risk for Alzheimer's disease (AD), both familial and sporadic, and that this risk is dose-dependent. Other genes that may play a role in AD, either through independent association with the disease or through modification of, or interaction with, the existing apolipoprotein E (APOE) risk, are now under investigation including the alpha-1-antichymotrypsin (ACT) gene, the very low density lipoprotein receptor (VLDL-R) gene, and the presenilin-1 (PS-1) gene. Kamboh et al. [1995] reported that a polymorphism in the alpha-1-antichymotrypsin gene could modify the risk for AD conferred by the APOE locus, specifically by increasing the risk for AD among epsilon 4 homozygotes. The ACT gene, which is found on chromosome 14, has previously been proposed as a candidate for AD due to the presence of the ACT protein in senile plaques and the reported elevation of the protein in the cerebro-spinal fluid (CSF) and serum of AD cases. We have investigated this reported association within our familial and sporadic AD dataset, where we find no independent association between ACT and the occurrence of AD. Logistic regression analysis excludes ACT or the interaction between ACT and APOE as significant contributors in the prediction of disease status. By this analysis, ACT genotyping does not provide additional information about an individual's risk of Alzheimer's disease beyond the risk information conferred by APOE genotype alone.

No association between the intronic presenilin-1 polymorphism and Alzheimer's disease in clinic and population-based samples.

Mutations in the Presenilin 1 (PS1) gene on chromosome 14 cause most early-onset familial Alzheimer's disease (AD). An intronic polymorphism in the PS1 gene was recently identified and reported to be associated with late-onset AD [Wragg et al., Lancet 347: 509-512, 1996]. The authors found an excess of homozygotes for the more common allele (allele 1) in AD cases, associated with an approximate doubling of risk. In the present study, we report the PS1 polymorphism distributions in clinic and population-based samples. We were not able to replicate the findings of Wragg et al. [1996]. Our results are consistent with those of other researchers and do not support the conclusion that the PS1 polymorphism is associated with late-onset AD.

No association between the very low density lipoprotein receptor gene and late-onset Alzheimer's disease nor interaction with the apolipoprotein E gene in population-based and clinic samples.

It is now commonly known that possession of one of the three common alleles of the apolipoprotein E (APOE) gene (allele epsilon 4) confers an increased risk for both familial and sporadic Alzheimer's disease (AD), and that this risk is dose-dependent. Other genes that may play a role in AD, either through independent association with the disease or through modification of the existing APOE risk, are under investigation. One such gene, the very low density lipoprotein receptor (VLDL-R) gene, was reported by Okuizumi et al. to be independently associated with AD in a Japanese population, but not interactive with the APOE4 conferred risk. Their clinic-based data set demonstrated a 2-fold increased risk conferred by the 5-repeat allele of a polymorphism in VLDL-R. As recruitment from a clinic rather than a population-based sample may result in a distortion of allele frequencies, as has been shown with APOE allele frequencies, it is important to investigate this association in a population-based study. We have genotyped both population and clinic-based AD data sets at this VLDL-R polymorphism, and we find no independent association between the VLDL-R gene and the occurrence of AD in either sample. Further, despite the biochemical relationship between the VLDL-R and APOE proteins, we find no significant statistical interaction between the alleles at these loci.

Familial and population-based studies of apolipoprotein E and Alzheimer's disease.

The finding of an association between the epsilon 4 allele of the APOE locus and the early expression of late-onset Alzheimer's disease (AD) is robust. However, the estimates of the proportion of AD cases carrying one or more copies of the epsilon 4 allele vary dramatically between studies (highest estimates being 180% of lowest ones). Here we compare the results of association studies in samples drawn from an epidemiologically based study design and samples drawn from families selected for linkage studies. The significant differences between results probably point to the unwitting selection of familial factors other than the APOE locus in the family history positive samples. We conclude that any selection procedure tending to enrich samples for positive family history will also tend to artificially increase APOE epsilon 4 allele frequencies in probands. This is of significance in samples drawn from clinical settings where referral may be influenced by previous known family history. Further work is needed to clarify the nature of the additional factors operating within families. We also report data showing an association between late-onset AD and a polymorphism in an adjacent locus to APOE-the APOCI locus. As no additional risk for AD can be attributed to the APOCI locus, the most likely explanation for the association between AD and APOCI is the disequilibrium between the APOCI and APOE loci. Therefore, there are likely to be other genetic markers in the area that can be used in the same way as APOE as a marker of risk for the disease.