Inhibition of natural killer cell activation signals by killer cell immunoglobulin-like receptors (CD158)

The killer cell immunoglobulin-like receptor (KIR) family includes receptors that bind to HLA class I molecules on target cells and inhibit natural killer (NK)-cell cytotoxicity, and receptors such as KIR3DL7 with no known ligand and function. Inhibitory KIR recruit the tyrosine phosphatase SHP-1 to block signals transduced by any one of a number of activation receptors. Inhibition of overall protein tyrosine phosphorylation by SHP-1 during binding of KIR to MHC class I on target cells is selective, suggesting that a limited number of substrates are dephosphorylated by SHP-1. We have chosen to study KIR inhibition as it occurs during binding of KIR to MHC class I on target cells, despite the technical limitations inherent to studies of processes regulated by cell contact. KIR binding to MHC class I on target cells inhibits tyrosine phosphorylation of the activation receptor 2B4 (CD244) and disrupts adhesion of NK cells to target cells. Inhibition of proximal events in NK activation may increase the availability of NK cells by liberating them from non-productive interactions with resistant target cells. As the receptors and the signaling pathways that induce NK cytotoxicity are not fully characterized, elucidation of the inhibitory mechanism employed by KIR may provide insight into NK activation.

Branched-chain amino acid aminotransferase activity decreases during development in skeletal muscles of sheep

The catabolism of branched-chain amino acid (BCAA) differs between sheep and monogastric animals. The transamination of BCAA seems to be affected by development of the sheep. We studied the developmental changes in the activity and expression of the BCAA aminotransferase (BCAT) isoenzymes in skeletal muscle of sheep. Five muscles were taken from fetus, newborn, preruminant and ruminant lambs. BCAT specific activity and the contribution of each BCAT isoenzyme [mitochondrial and cytosolic (BCATm and BCATc, respectively)] were quantified using radioenzymatic and immunoprecipitation assays. BCATm and BCATc mRNAs were assessed by real-time reverse transcription-polymerase chain reaction. BCAT specific activities were 62% (diaphragma) to 83% (longissimus dorsi) lower in the ruminant lamb than in the fetal sheep. BCATm and BCATc were both expressed in sheep skeletal muscle at all developmental stages. BCATc was mainly responsible for the developmental decrease in BCAT specific activity. BCATc specific activities were 77% (diaphragma) to 92% (longissimus dorsi) lower in the ruminant lamb than in the fetal sheep, whereas BCATm specific activities were only 36% (semimembranosus) to 56% (longissimus dorsi) lower. BCATc and BCATm mRNAs in the longissimus dorsi were not affected by development of the sheep. The developmental decrease in BCATc activity, and to a lesser extent in BCATm activity, probably involves posttranscriptional mechanisms in sheep. The present results are consistent with lower in vivo metabolism of BCAA in ruminant than in the fetal sheep.

[Cutaneous adverse drug reactions: enhanced imputation score by skin testing]

INTRODUCTION

A careful diagnosis and the identification of the causative drug after a cutaneous adverse reaction can avoid relapses. Skin tests facilitate the identification of the causative molecule by producing a hypersensitivity reaction at the application site. Adverse drug reactions are reported to Pharmacovigilance Centres who determine the imputation score of the suspected drugs. The aim of this study was to assess to what extent skin testing after a suspected allergic drug reaction can be helpful to identify the causative drug and whether an impact on the final imputation score could be evidenced.

METHOD

A 18-month prospective study was performed. All patients with a history of cutaneous adverse drug reaction of suspected immunoallergic origin were included provided skin tests could be performed within 6 to 12 weeks after the adverse drug reaction. The imputation score was determined using the French imputation method prior to and after skin testing.

RESULTS

Thirthy-nine patients were included in the study. Positive skin tests were observed in 11 of 20 patients with a C2S2 (I2: plausible) initial imputation score and in 6 of 15 patients with a C2S1 (I1: doubtful) initial imputation score. One patient with a C1S1 (I1: doubtful) initial imputation score had positive skin tests.

DISCUSSION

The results of skin tests helped change the imputation score of the suspected drug in 18 patients out of 39. In 55 p. 100 of cases, the imputation score was increased from C2S2 (I2) to C2S3 (I3: likely) and from C2S1 (I1) to C2S3 (I3) in 40 p. 100 of cases. The increase in imputation scores was helpful to improve warning signals after an immunoallergic reaction. Skin tests led to a more accurate diagnosis in 50 p. 100 of cases. Thus, more adequate advices for further drug treatment were possible, particularly in avoiding the irrelevant prohibition of innocent drugs.

Undergraduate research student perceptions

Health professionals are required to generate evidence via research in order to validate their practice. Undergraduate students in the professions allied to medicine complete a research component in their final year of study. The assumption is that this component will equip them with the knowledge, skills and attitudes to undertake research as clinicians. In this retrospective study, a questionnaire was used to examine the perceptions and experiences of students relating to their research projects. The study population was students studying in the professions allied to medicine on the Tygerberg Campus of the University of Stellenbosch.The response rate was 77% (n-106). Of these students, 69% enjoyed implementing their research project, whilst 28% did not. However, physiotherapy students experienced this component of their course most negatively. The most positive perceptions of the students related to educational benefits and interest, whilst the most negative results related to time restraints and stress.In planning for the future, it is important to evaluate the outcomes of the research component of the undergraduate curriculum and its possible effects on the development and practice of the physiotherapy profession

Sheep cytosolic branched-chain amino acid aminotransferase: cDNA cloning, primary structure and molecular modelling and its unique expression in muscles

This paper presents the cloning and the molecular modelling of the cytosolic branched-chain amino acid aminotransferase (BCATc) from sheep brain. The sheep BCATc cDNA (3 kb) encodes a mature polypeptide of 385 amino acids with a calculated molecular mass of 43072.93 Da. The sequence of the sheep BCATc cDNA is more similar to other mammalian BCATc cDNAs (53-87% identical) than to the sheep mitochondrial branched-chain amino acid aminotransferase (52%). Sheep BCATc belongs to the IV Folding class of pyridoxal-5'-phosphate-depending enzymes. Based on the known structure of the branched-chain amino acid aminotransferase (BCAT) from Escherichia coli, a molecular model of sheep BCATc (amino acid residues 62-385) was built. This is the first three-dimensional model of any mammalian BCAT. It suggests that the enzymatic mechanism of sheep BCATc and likely of all mammalian BCAT is very similar to the mechanism of the E. coli BCAT and confirms the hypotheses regarding to the substrate binding sites of E. coli BCAT. Sheep skeletal muscle, which is the main in vivo site for transamination of branched-chain amino acids, exhibits an unique expression of BCATc.

[Perianal streptococcal dermatitis]

BACKGROUND

Pediatric perianal streptococcal dermatitis (PSD) is a well-defined clinical entity. However, its highly uniform presentation remains surprisingly unrecognized by many practitioners 33 years after its first description.

CASE REPORT

A seven-year-old girl had a three-week history of perianal and vulva redness with well-defined margins. Functional symptoms associated perirectal tenderness and pain during defecation, which was responsible for constipation. At onset she also presented with a sore throat, which resolved spontaneously, and she had been complaining for a few days about a perioral impetigo. She received mycostatin unsuccessfully for an alleged candidiasis. Positive cultures for group A beta-hemolytic streptococci from both perirectal and perioral swabs confirmed the diagnosis of PSD. Therapy with amoxicillin (50 mg/kg/d) was prescribed for ten days. Perianal lesions were cleared by day 2.

CONCLUSION

Since PSD can masquerade as candidiasis, psoriasis, seborrheic dermatitis, inflammatory bowel disease or even sexual abuse, it remains an underdiagnosed entity. This situation leads to delayed diagnosis and treatment which in turn might increase the frequency of secondary complications related to streptococcal infections (i.e., post-streptococcal acute nephritis and rheumatism, guttate psoriasis, etc.).

Merkel cells in hyperplastic and neoplastic lesions of the skin. An immunohistochemical study using an antibody to keratin 20

BACKGROUND

Merkel cells are neuro-endocrine cells present in the basal layer of the human epidermis and the outer root sheath of hair follicles.

OBJECTIVE AND METHOD

In order to gain further insight into the as yet ill-defined involvement of Merkel cells in skin diseases, we studied the distribution of these cells in formalin-fixed, paraffin-embedded sections of 165 inflammatory, hyperplastic or tumoral skin lesions of various anatomic locations, with a monoclonal antibody to keratin 20.

RESULTS

Lesions with frequently increased Merkel Cell numbers included actinic keratosis, fibrous papules of the face and some conditions with (immature) hair follicle differentiation.

CONCLUSION

These results suggest that Merkel cell hyperplasia is unrelated to epidermal proliferation but that it is rather specific to a limited number of skin diseases.

Interaction between the lipoamide-containing H-protein and the lipoamide dehydrogenase (L-protein) of the glycine decarboxylase multienzyme system. 1. Biochemical studies

Lipoamide dehydrogenase or dihydrolipoamide dehydrogenase (EC 1.8.1. 4) is the E3-protein component of the mitochondrial 2-oxoacid dehydrogenase multienzyme complexes. It is also the L-protein component of the glycine decarboxylase system. Although the enzymology of this enzyme has been studied exhaustively using free lipoamide as substrate, no data are available concerning the kinetic parameters of this enzyme with its physiological substrates, the dihydrolipoyl domain of the E2 component (dihydrolipoyl acyltransferase) of the 2-oxoacid dehydrogenase multienzyme complexes or the dihydrolipoyl H-protein of the mitochondrial glycine decarboxylase. In this paper, we demonstrate that Tris(2-carboxyethyl)phosphine, a specific disulfide reducing agent, allows a continuous reduction of the lipoyl group associated with the H-protein during the course of the reaction catalysed by the L-protein. This provided a valuable new tool with which to study the catalytic properties of the lipoamide dehydrogenase. The L-protein displayed a much higher affinity for the dihydrolipoyl H-protein than for free dihydrolipoamide. The oxidation of the dihydrolipoyl H-protein was not affected by the presence of structurally related analogues (apoH-protein or octanoylated H-protein). In marked contrast, these analogues strongly and competitively inhibited the decarboxylation of the glycine molecule catalysed by the P-protein component of the glycine decarboxylase system. Small unfolded proteolytic fragments of the H-protein, containing the lipoamide moiety, displayed Km values for the L-protein close to that found for the H-protein. On the other hand, these fragments were not able to promote the decarboxylation of the glycine in the presence of the P-protein. New highly hydrophilic lipoate analogues were synthesized. All of them showed Km and kcat/Km values very close to that found for the H-protein. From our results we concluded that no structural interaction is required for the L-protein to catalyse the oxidation of the dihydrolipoyl H-protein. We discuss the possibility that one function of the H-protein is to maintain a high concentration of the hydrophobic lipoate molecules in a nonmicellar state which would be accessible to the catalytic site of the lipoamide dehydrogenase.

Interaction between the lipoamide-containing H-protein and the lipoamide dehydrogenase (L-protein) of the glycine decarboxylase multienzyme system 2. Crystal structures of H- and L-proteins

The glycine decarboxylase complex consists of four different component enzymes (P-, H-, T- and L-proteins). The 14-kDa lipoamide-containing H-protein plays a pivotal role in the complete sequence of reactions as its prosthetic group (lipoic acid) interacts successively with the three other components of the complex and undergoes a cycle of reductive methylamination, methylamine transfer and electron transfer. With the aim to understand the interaction between the H-protein and its different partners, we have previously determined the crystal structure of the oxidized and methylaminated forms of the H-protein. In the present study, we have crystallized the H-protein in its reduced state and the L-protein (lipoamide dehydrogenase or dihydrolipoamide dehydrogenase). The L-protein has been overexpressed in Escherichia coli and refolded from inclusion bodies in an active form. Crystals were obtained from the refolded L-protein and the structure has been determined by X-ray crystallography. This first crystal structure of a plant dihydrolipoamide dehydrogenase is similar to other known dihydrolipoamide dehydrogenase structures. The crystal structure of the H-protein in its reduced form has been determined and compared to the structure of the other forms of the protein. It is isomorphous to the structure of the oxidized form. In contrast with methylaminated H-protein where the loaded lipoamide arm was locked into a cavity of the protein, the reduced lipoamide arm appeared freely exposed to the solvent. Such a freedom is required to allow its targeting inside the hollow active site of L-protein. Our results strongly suggest that a direct interaction between the H- and L-proteins is not necessary for the reoxidation of the reduced lipoamide arm bound to the H-protein. This hypothesis is supported by biochemical data [Neuburger, M., Polidori, A.M., Piètre, E., Faure, M., Jourdain, A., Bourguignon, J., Pucci, B. & Douce, R. (2000) Eur. J. Biochem. 267, 2882-2889] and by small angle X-ray scattering experiments reported herein.

Multiple eruptive dermatofibromas in a patient with HIV infection: case report and literature review

Multiple eruptive dermatofibromas have been reported in the setting of autoimmune diseases treated with immunosuppressive drugs and more recently in the course of human immunodeficiency virus (HIV) infection. We report herein the ninth case of multiple eruptive dermato fibromas associated with HIV infection. The relevant literature is reviewed and the differences of these lesions from "ordinary" dermatofibromas are discussed.

Tolerance to maternal immunoglobulins: resilience of the specific T cell repertoire in spite of long-lasting perturbations

T cell tolerance is established and maintained through various mechanisms, the critical component being the persistence of the specific Ag. However, at the molecular level, the nature of the recovering TCR repertoire following breakdown of tolerance is unknown. We address this important question by following kappa light chain constant region (C kappa)-specific CD4+ T cells of kappa light chain knock-out (kappa-/-) mice born to kappa+/- mothers. These cells, which were in contact with maternal kappa+ Igs from early ontogeny until weaning, were strongly tolerized. Tolerance was reversible and waned with the disappearance of peptide C kappa 134-148 presentation in lymphoid organs, including the thymus. Whereas three specific V beta-J beta rearrangements emerged in the peptide C kappa 134-148-specific CD4+ T cell response of all regular kappa-/- mice, soon after breakdown of tolerance only one of these rearrangements was detected. The two others displayed a significant delay in reappearance and were still rare at 26 wk of age, while the control proliferative response had already recovered 3 mo earlier. At 52 wk of age, a complete recovery of the three canonical V beta-J beta rearrangements was observed. Thus, although profoundly perturbed for several months, the T cell repertoire returns to equilibrium, highlighting the resilient nature of this system.

[Proliferative characteristics of nevus in children with organ transplants]

INTRODUCTION

Organ-graft recipients are at increased risk for developing cutaneous tumors, mostly carcinomas; however, melanocytic nevi (MN) also develop in excess numbers in these patients. The aim of this study was to assess whether MN developing in pediatric organ graft recipients (OGR-MN) have a higher proliferative profile than similar lesions developing in non-immunosuppressed subjects (C-MN), a fact that could confer to them potential for malignant transformation into melanoma.

MATERIAL AND METHODS

The immunohistochemical expression of two proliferation-associated markers (MIB1/Ki67 and PCNA) and of p53 oncoprotein was comparatively studied in a group of 10 and OGR-MN and 12 C-MN.

RESULTS

MIB1/Ki67 and p53 were very weakly, if at all, expressed in all tumors, whereas PCNA was expressed in the majority of tumor cells in both groups of lesions. Overall, no significant differences were found between the two groups studied.

DISCUSSION

Melanocytic nevi developing in organ transplant children do not have a higher proliferative potential, and therefore do not seem to be intrinsically more prone to malignant transformation than similar lesions appearing in non-immunosuppressed children; however the possibility exists that the decreased immune defense mechanisms indirectly favors the growth of these lesions.

Paroxetine in social phobia/social anxiety disorder. Randomised, double-blind, placebo-controlled study. Paroxetine Study Group

BACKGROUND

Preliminary studies have suggested that paroxetine may be effective in social phobia/social anxiety disorder.

AIMS

To assess the efficacy and tolerability of paroxetine in the acute (12-week) treatment of social phobia.

METHOD

Two-hundred and ninety patients with social phobia were assigned randomly to paroxetine (20-50 mg/day flexible dose) or placebo for 12 weeks of double-blind treatment. Primary efficacy outcomes were the Liebowitz Social Anxiety Scale (LSAS) total score (patient-rated) and the Clinical Global Impression (CGI) scale global improvement item. The secondary efficacy variables included CGI scale severity of illness score and the patient-rated Social Avoidance and Distress Scale.

RESULTS

Paroxetine produced a significantly greater reduction in LSAS total score (mean change from baseline: -29.4 v. -15.6; P < or = 0.001) and a greater proportion of responders (score < or = 2 on CGI global improvement) (65.7% v. 32.4%; P < 0.001) compared with placebo at the end of the 12-week study period. Both primary efficacy variables were statistically significant compared with placebo from week 4 onwards. Paroxetine was generally well tolerated.

CONCLUSIONS

Paroxetine is an effective, well-tolerated treatment for patients with social phobia.

Presence of circulating abnormal CD34+ progenitors in adult Langerhans cell histiocytosis

Langerhans cell histiocytosis (LCH) is related to the proliferation of cells, which are similar to Langerhans cells (LC) but possess many abnormal characteristics. Lesions are widespread and this fact suggests that LCH cells or their precursors are present in the blood of patients. In five adult patients, we have isolated and cultured CD34+ blood progenitors of dendritic cells. We studied their phenotype by flow cytometry and their functional properties in mixed culture with heterologous lymphocytes and with autologous lymphocytes in the presence of tri-nitro-phenyl antigen (TNP). The amount of CD34+ precursors was dramatically higher than controls but a high mortality occurred during the in vitro differentiation. The phenotype of surviving cells was similar to LC phenotype (CD1a+, CD83+, Lag+) but some of them expressed CD2. These cells were able to induce T cell proliferation in mixed culture. They could not initiate primary response to TNP, except in a patient treated with thalidomide. In our hands, these CD34+ cells may be precursors of LCH cells.

Expression of basement membrane antigens and matrix metalloproteinases 2 and 9 in cutaneous basal and squamous cell carcinomas

BACKGROUND

Basement membrane (BM) antigens and matrix metalloproteinases (MMP) are involved in tumor invasion and metastasis. Basal (BCC) and squamous cell carcinomas (SCC) differ with respect to their biological behavior since the former are only locally aggressive whereas the latter have a metastatic potential.

MATERIALS AND METHODS

We studied the immunohistochemical expression of several BM antigens and of MMP2 and MMP9, in 13 BCC, 13 SCC, and 8 in situ skin carcinomas.

RESULTS

The expression of most BM antigens was reduced in the tumors in comparison with normal skin. Hemidesmosome- and lamina lucida-associated antigens (plectin, NUT2, alpha 6/CD49f and laminin-5) were more decreased in BCC, whereas collagens type VII and IV were more decreased in SCC as compared with BCC; in BCC and SCC both collagens tended to be decreased on the leading edge of invasive tumor masses. In situ carcinomas showed a slightly diminished expression of alpha 6/CD49f integrin, plectin and NUT2. The expression of both MMP2 and MMP9 was increased in SCC as compared with BCC.

CONCLUSION

Our findings further upheld the role of BM antigens and MMPs in the process of tumor aggressiveness. The reduced expression of collagen IV, combined with an increased expression of both MMP2 and MMP9 could account for the increased metastatic potential of SCC vs BCC through an increased invasion of the extracellular matrix and the vascular space.