Major histocompatibility complex haplotypes and the cell physiology of peptide hormones

Open MHC Class I Conformers: A Look through the Looking Glass

Studies carried out during the last few decades have consistently shown that cell surface MHC class I (MHC-I) molecules are endowed with functions unrelated with antigen presentation. These include cis–trans-interactions with inhibitory and activating KIR and LILR, and cis-interactions with receptors for hormones, growth factors, cytokines, and neurotransmitters. The mounting body of evidence indicates that these non-immunological MHC-I functions impact clinical and biomedical settings, including autoimmune responses, tumor escape, transplantation, and neuronal development. Notably, most of these functions appear to rely on the presence in hematopoietic and non-hematopoietic cells of heavy chains not associated with β2m and the peptide at the plasma membrane; these are known as open MHC-I conformers. Nowadays, open conformers are viewed as functional cis-trans structures capable of establishing physical associations with themselves, with other surface receptors, and being shed into the extracellular milieu. We review past and recent developments, strengthening the view that open conformers are multifunctional structures capable of fine-tuning cell signaling, growth, differentiation, and cell communication.

Improving Cancer Drug Discovery by Studying Cancer across the Tree of Life

Despite a considerable expenditure of time and resources and significant advances in experimental models of disease, cancer research continues to suffer from extremely low success rates in translating preclinical discoveries into clinical practice. The continued failure of cancer drug development, particularly late in the course of human testing, not only impacts patient outcomes, but also drives up the cost for those therapies that do succeed. It is clear that a paradigm shift is necessary if improvements in this process are to occur. One promising direction for increasing translational success is comparative oncology-the study of cancer across species, often involving veterinary patients that develop naturally-occurring cancers. Comparative oncology leverages the power of cross-species analyses to understand the fundamental drivers of cancer protective mechanisms, as well as factors contributing to cancer initiation and progression. Clinical trials in veterinary patients with cancer provide an opportunity to evaluate novel therapeutics in a setting that recapitulates many of the key features of human cancers, including genomic aberrations that underly tumor development, response and resistance to treatment, and the presence of comorbidities that can affect outcomes. With a concerted effort from basic scientists, human physicians and veterinarians, comparative oncology has the potential to enhance the cost-effectiveness and efficiency of pipelines for cancer drug discovery and other cancer treatments.

Characterization of the pulmonary lesions induced in rats by human recombinant interleukin-2

Histologic, electron microscopic, and immunohistochemical studies were made to analyze the structural features and the cellular composition of the pulmonary lesions produced in rats by the administration of interleukin-2 (IL-2). This agent induced pulmonary edema; thickening of alveolar septa; damage to endothelial cells in capillaries and venules, marked interstitial infiltration by cytotoxic T lymphocytes, lymphokine-activated killer (LAK) cells, macrophages, and dendritic cells (as demonstrated by cell counting in preparations stained immunohistochemically with peroxidase- and fluorochrome-labeled antibodies); and injury to bronchiolar and alveolar epithelial cells. Granular and agranular lymphocytes often were closely apposed to endothelial cells in capillaries and venules. Contacts between lymphocytes and type II alveolar epithelial cells also were observed. Damaged type II alveolar epithelial cells showed nuclear and cytoplasmic features that are considered indicative of apoptosis (confirmed by nick end labeling). Phagocytosis of apoptotic bodies by macrophages was occasionally found. These results support the concept that IL-2 induces cytotoxic vascular and parenchymal cell damage that is mediated by LAK cells and cytotoxic T lymphocytes, which make contacts with endothelial cells and type II alveolar epithelial cells. This damage appears to be exacerbated by the secondary release of a variety of vasoactive agents and inflammatory mediators.

Proximity measurements between H-2 antigens and the insulin receptor by fluorescence energy transfer: evidence that a close association does not influence insulin binding

Reports based on coprecipitation experiments have suggested that major histocompatibility complex class I products are complexed with the insulin receptor on the cell surface. Using an independent method that avoids the creation of immunoprecipitation artifacts during membrane solubilization, we have studied insulin receptor-class I product associations by determining the proximity between these class I products and the insulin receptor on intact cells with the use of fluorescence energy transfer. Significant energy transfer was seen between the insulin receptor and both murine H-2K- as well as H-2D-end products, indicating close proximity (e.g., within 10 nm). This cell-surface association is not from the relatively high class I density in that no significant energy transfer was measured between H-2K- vs. H-2D-end proteins. To extend these observations, we also tested whether class I products influence insulin-receptor binding and postbinding events as a result of their physical association. Using related cell lines positive and negative for class I expression, we found no correlation between insulin-receptor density or binding affinity with H-2 product expression. The class I-null variant, however, demonstrated an increase in insulin-mediated insulin-receptor internalization to suggest that if major histocompatibility complex class I products directly affect insulin-receptor function through specific cell-surface interactions, they may do so after ligand binding.

A novel H-2K splice form: predictions for other alternative H-2 splicing events

A large number of H-2K and H-2D cDNA clones from a C3HfB/HeN spleen cDNA library were extensively characterized. All H-2Dk cDNAs were shown to exhibit the short form of exon 8, consistent with the presence of a single lariat branchpoint site within intron 7. Twenty-five H-2Kkm2 cDNAs were found to bear a short exon 8, whereas only two clones were shown to carry the longer form of this exon. In one of the H-2Kkm2 cDNAs, a novel pattern of H-2 splicing was identified, in which an extra 15 nucleotides, derived from the 3' end of intron 5, were inserted between the intact and unaltered exon 5 and exon 6 sequences. Resulting from the apparent use of a cryptic splice acceptor site in place of the canonical intron 5 site, this insertion is predicted to generate an in-frame insertion of five nonpolar amino acid residues within a highly polar region of the intracytoplasmic domain of the H-2K polypeptide. The features of this novel splice form served as the basis for predicting additional rare, alternative H-2 pre-mRNA splicing events that might produce functionally relevant microheterogeneity in the encoded H-2 gene products.

Identification of an alternatively spliced Kd and the Qa-6d mRNAs by using amplified cDNA

We have employed the primer chain reaction method for direct sequencing of H-2 mRNAs. This approach is highly sensitive and permits quantitation and sequencing of the canonical as well as alternatively spliced mRNAs that may be expressed at 5-10% level in comparison to the major H-2 species. Using this technique, we have identified a novel species of alternatively spliced Kd mRNA expressed in L1210 lymphoma and in the spleen and liver of DBA/2 mice. Similarly, we found a previously described alternatively spliced species of H-2Dd mRNA to be expressed in L1210 lymphoma and have determined the sequence of the cytoplasmic domain of Ld mRNA. In addition, we have identified a Class I MHC transcript presumably encoded by a gene allelic to Q6 gene of BALB/c mice.

H-2K molecules have two different C-termini, one of which is K-region specific

Amino acid sequences encoded by exon 8 of the H-2K and H-2D/L genes appear to be locus specific. The majority of H-2Kb molecules contain 10 amino acids that are derived from exon 8. In contrast, the H-2Db, -Dd and -Ld molecules contain only one amino acid which is encoded by exon 8, even though the genetic information exists to encode 10 amino acids analogous to those encoded by the majority of H-2Kb transcripts. We have produced a rabbit anti-peptide serum reactive with the exon 8 encoded sequence of H-2Kb (alpha K-C) that specifically immunoprecipitates a molecule of 45 K mol. wt from spleen cell lysates of b, d, p, q and k haplotype mice. Further analysis by Western blots indicated that virtually all mouse strains express a 45 K protein reactive with alpha K-C. In sequential immunoprecipitations of spleen cell lysates from b, q, p and d haplotype mice using alpha K-C followed by H-2K or H-2D private specificity alloantisera, the anti-peptide serum removed nearly all of the molecules reactive with the anti-H-2K alloantisera (except in the k haplotype) and none of the molecules reactive with the anti-H-2D serum. In addition, no D-region molecules possessing a long C-terminal sequence were detected with an antiserum directed against a representative D-region long C-terminal peptide. We conclude that even though the genetic information for an extended exon 8 exists in K, D and L locus genes, apparently only K-region molecules are expressed with such a C-terminus. Furthermore, in most haplotypes the great majority of H-2K molecules are produced using long exon 8; however, H-2Kk is produced mostly from short exon 8. The absence or presence of key adenosine residues is predicted to be responsible for the variability in class I exon 8 splicing.

Major histocompatibility antigens on trophoblast and their regulation: implications in the maternal-fetal relationship

Recent technological advances have provided methods of detecting antigens encoded by the major histocompatibility complex with greater precision, allowing the expression of such antigens on the components of the placenta to be clarified. Of specific interest is the expression of these antigens on trophoblast cells, the fetal-derived epithelial cells that confront maternal blood and tissues at the maternal-fetal interface. It is now clear that the different trophoblast subpopulations differentially express class I antigens, although none appear to express class II antigens. Class I antigens can be induced by exposure to interferons on some populations but apparently not others, suggesting that the regulation of their expression differs for subpopulations of trophoblast cells, depending on gestational stage and location. This restricted expression has important implications for maternal-fetal immune interactions during the different phases of pregnancy and perhaps also bears on physiological functions of the feto-placental unit, such as growth and differentiation.