Accessory molecules in the assembly of major histocompatibility complex class I/peptide complexes: how essential are they for CD8+ T‐cell immune responses?

Summary: Assembly of major histocompatibility complex (MHC) class I molecules in the endoplasmic reticulum is a highly coordinated process that results in abundant class I/peptide complexes at the cell surface for recognition by CD8⁺ T cells and natural killer cells. During the assembly process, a number of chaperones and accessory molecules, such as transporter associated with antigen processing, tapasin, ER60, and calreticulin, assist newly synthesized class I molecules to facilitate loading of antigenic peptides and to optimize the repertoire of surface class I/peptide complexes. This review focuses on the relative importance of these accessory molecules for CD8⁺ T‐cell responses in vivo and discusses reasons that may help explain why some CD8⁺ T‐cell responses develop normally in mice deficient in components of class I assembly, despite impaired antigen presentation.     

Clinical and immunological features of adult-onset generalized autoimmune gut disorder

OBJECTIVES: Autoimmune enteropathy is a rare disorder of unknown pathogenesis, characterized by protracted diarrhea, villous atrophy, and enterocyte autoantibodies. Its association with extended inflammation of the whole gastrointestinal tract is termed as generalized autoimmune gut disorder (GAGD), generally a pediatric disease of difficult management due to its association with immunodeficiency. The aim of our work is to describe the mucosal immunological basis of an adult-onset case of GAGD. METHODS: We studied an adult female with a severe inflammatory involvement of the gastrointestinal tract (stomach, small and large bowel, and liver) and antienterocyte autoantibodies. She had antibody deficiency and a predisposition to systemic autoimmunity. We analyzed, by immunohistochemistry and flow cytometry, the phenotypic and functional characteristics of her intestinal intraepithelial and lamina propria (LP) lymphocytes. RESULTS: We observed the prominent and constant presence of an unusual CD4+alphaE/beta7- Tc subset in the jejunal epithelium. Signs of the lymphocyte activation as well as the prominent lymphoid TNF-alpha production observed in the rectal mucosa support the involvement of a cell-mediated pro-inflammatory response in the pathogenesis of GAGD. CONCLUSIONS: We report the second case of an adult fulfilling all diagnostic criteria for GAGD. We propose that the activated LP CD4+ T lymphocytes, as well as those atypically located in the epithelium, may play a pathogenic role. The alphaE/beta7- IEL could constitute a diagnostic marker of intestinal autoimmunity in the cases when autoantibodies are not evidenced, and mucosal TNF-alpha might represent a novel therapeutic target in this severe disease.     

Flow cytometric analysis of intestinal intraepithelial lymphocytes in the diagnosis of refractory celiac sprue

The etiology of refractory celiac sprue (RCS) is unclear. In a high proportion of cases, the clonal nature of intestinal intraepithelial lymphocytes (IEL) can be demonstrated and a pathogenetic implication of intestinal IEL has been postulated. The prognosis of this subgroup of RCS is poor, with a high risk to develop an overt lymphoma and uncontrolled malabsorption despite steroid/immunosuppressive therapy. Cases with a relatively indolent clinical course, however, exist and their early diagnosis may be difficult. To gain insight into the pathogenic implication of intestinal IEL in refractory celiac sprue, we have performed an extensive phenotypic and functional characterization of clonal intestinal IEL in a patient with an indolent form of refractory celiac sprue, using multiparametric flow cytometry. The abnormal lymphocyte infiltrate lacked surface membrane expression of CD3/T-cell receptor (TCR) complexes (TCR(-), CD4(-), CD8(-), sCD3(-)), but contained intracellular CD3(epsilon) (CyCD3(+)) and surface CD103(+) and CD7(+). In particular, these cells showed a unique spontaneous ex-vivo cytokine secretion profile with an increased percentage of CD3(-) IEL containing TNF-alpha and IL-10, in the absence of IL-2, IL-4 and IFN-gamma. Altogether our results suggest that flow cytometry immunophenotyping of intestinal IEL, in cases suspected of celiac disease and their complicated forms, could be of great help in the correct diagnosis of RCS and the understanding of the immunopathogenic mechanisms of the disease and their clinical and/or therapeutical implications.     

ER Stress During the Pubertal Growth Spurt Results in Impaired Long‐Bone Growth in Chondrocyte‐Specific ERp57 Knockout Mice

Long‐bone growth by endochondral ossification is cooperatively accomplished by chondrocyte proliferation, hypertrophic differentiation, and appropriate secretion of collagens, glycoproteins, and proteoglycans into the extracellular matrix (ECM). Before folding and entering the secretory pathway, ECM macromolecules in general are subject to extensive posttranslational modification, orchestrated by chaperone complexes in the endoplasmic reticulum (ER). ERp57 is a member of the protein disulfide isomerase (PDI) family and facilitates correct folding of newly synthesized glycoproteins by rearrangement of native disulfide bonds. Here, we show that ERp57‐dependent PDI activity is essential for postnatal skeletal growth, especially during the pubertal growth spurt characterized by intensive matrix deposition. Loss of ERp57 in growth plates of cartilage‐specific ERp57 knockout mice (ERp57 KO) results in ER stress, unfolded protein response (UPR), reduced proliferation, and accelerated apoptotic cell death of chondrocytes. Together this results in a delay of long‐bone growth with the following characteristics: (1) enlarged growth plates; (2) expanded hypertrophic zones; (3) retarded osteoclast recruitment; (4) delayed remodeling of the proteoglycan‐rich matrix; and (5) reduced numbers of bone trabeculae. All the growth plate and bone abnormalities, however, become attenuated after the pubertal growth spurt, when protein synthesis is decelerated and, hence, ERp57 function is less essential. © 2015 American Society for Bone and Mineral Research.     

Female striated urogenital sphincter contraction measured by shear wave elastography during pelvic floor muscle activation: Proof of concept and validation

Aims

Investigation of the function of the striated urogenital sphincter (SUS) is challenging because it is difficult to access and requires invasive measures. Ultrasound shear wave elastography (SWE) is a non‐invasive real‐time technique used to estimate tissue stiffness. As muscle stiffness can be used as an estimate of muscle force, SWE provides an opportunity to study contraction of the peri‐urethral musculature. Validation of SWE to study SUS during functional tasks, such as pelvic floor muscle contractions, is required prior to application in clinical populations.

Methods

Ten healthy females (34[5] years) participated. Stiffness in a region expected to contain the SUS was quantified using SWE at rest and during a pelvic floor muscle contractions performed at 10%, 25%, and 50% of maximal voluntary contraction (MVC). Two repetitions were performed for 10 s.

Results

During contraction, stiffness increased in the region of the SUS in all participants and at all contraction intensities. Multiple regions of increased stiffness were detected, with 95.8% of regions situated ventral to the mid‐urethra within the anatomical area of the SUS. The increase in stiffness was greater for 50% MVC than both 10% and 25% MVC contraction intensities (P < 0.01).

Conclusions

Stiffness increased within the anatomical region of the SUS during voluntary pelvic floor muscle contractions with predictable response to changes in contraction intensity. These observations support the potential for ultrasound SWE to study SUS function non‐invasively.     

Heart and heart-lung transplantation. 3 years' experience in Timone CHU (Marseilles 1985-1988)

Since December 1985, we have performed 38 transplantations: cardiac (CT) n: 31, cardiopulmonary (CPT) n: 1, or bipulmonary (BPT) n: 6. There were 31 male and 7 female patients, aged 7 to 62, mean 46. In the cardiac group, the cardiomyopathy was primitive in 13, ischemic in 16, valvular in 2. Five patients had undergone one or more previous operations. Three patients had a biventricular assist device (1,6 and 7 days before transplant) for acute cardiac failure. The indication of CPT or BPT was pulmonary artery hypertension (1), silicosis (1), cystic fibrosis (4). There were 4 post-operative deaths in the CT group (12.9%); failure of graft, low cardiac output, pulmonary artery hypertension by multiple pulmonary thrombosis, and 2 deaths in the CPT and BPT groups (28%). The mean post-operative hospital stay was one month. All patients with CT were treated by an initial maintenance bitherapy protocol (cyclosporine, steroids) and observed by myocardial biopsies and echocardiograms. In 40 per cent of the patients, Azathioprine was subsequently added. The patients had 2.1 rejection episode/patient/year, either spontaneously reversed of treated medically. There were two late deaths (2 and 7 months) by refractory rejection. 78 per cent of the patients were alive one year after transplant. All survivors have recovered a normal life, some of them with full-time work.(ABSTRACT TRUNCATED AT 250 WORDS)     

Interaction of ERp57 and tapasin in the generation of MHC class I-peptide complexes

Antigen presentation by MHC class I molecules is necessary for CD8 T-cell activation. Optimal peptide loading onto MHC class I molecules occurs mainly in the peptide-loading complex in the endoplasmic reticulum. The identification of a covalent association between the thiol oxidoreductase ERp57 and tapasin, and its impact on the loading complex, are important recent developments in this field of research. In the absence of ERp57, the recruitment of MHC class I molecules into this complex by tapasin is greatly impaired both in the number of molecules and in their interaction time, suggesting a key structural role for the ERp57-tapasin association in the peptide-loading complex. The role of ERp57 as a thiol oxidoreductase in the peptide-loading complex remains, however, controversial and further research regarding this subject is required.