The structural landscape and diversity of Pyricularia oryzae MAX effectors revisited

Magnaporthe AVRs and ToxB-like (MAX) effectors constitute a family of secreted virulence proteins in the fungus Pyricularia oryzae (syn. Magnaporthe oryzae), which causes blast disease on numerous cereals and grasses. In spite of high sequence divergence, MAX effectors share a common fold characterized by a ß-sandwich core stabilized by a conserved disulfide bond. In this study, we investigated the structural landscape and diversity within the MAX effector repertoire of P. oryzae. Combining experimental protein structure determination and in silico structure modeling we validated the presence of the conserved MAX effector core domain in 77 out of 94 groups of orthologs (OG) identified in a previous population genomic study. Four novel MAX effector structures determined by NMR were in remarkably good agreement with AlphaFold2 (AF2) predictions. Based on the comparison of the AF2-generated 3D models we propose a classification of the MAX effectors superfamily in 20 structural groups that vary in the canonical MAX fold, disulfide bond patterns, and additional secondary structures in N- and C-terminal extensions. About one-third of the MAX family members remain singletons, without strong structural relationship to other MAX effectors. Analysis of the surface properties of the AF2 MAX models also highlights the high variability within the MAX family at the structural level, potentially reflecting the wide diversity of their virulence functions and host targets.

Adaptive evolution in virulence effectors of the rice blast fungus Pyricularia oryzae

Plant pathogens secrete proteins called effectors that target host cellular processes to promote disease. Recently, structural genomics has identified several families of fungal effectors that share a similar three-dimensional structure despite remarkably variable amino-acid sequences and surface properties. To explore the selective forces that underlie the sequence variability of structurally-analogous effectors, we focused on MAX effectors, a structural family of effectors that are major determinants of virulence in the rice blast fungus Pyricularia oryzae. Using structure-informed gene annotation, we identified 58 to 78 MAX effector genes per genome in a set of 120 isolates representing seven host-associated lineages. The expression of MAX effector genes was primarily restricted to the early biotrophic phase of infection and strongly influenced by the host plant. Pangenome analyses of MAX effectors demonstrated extensive presence/absence polymorphism and identified gene loss events possibly involved in host range adaptation. However, gene knock-in experiments did not reveal a strong effect on virulence phenotypes suggesting that other evolutionary mechanisms are the main drivers of MAX effector losses. MAX effectors displayed high levels of standing variation and high rates of non-synonymous substitutions, pointing to widespread positive selection shaping the molecular diversity of MAX effectors. The combination of these analyses with structural data revealed that positive selection acts mostly on residues located in particular structural elements and at specific positions. By providing a comprehensive catalog of amino acid polymorphism, and by identifying the structural determinants of the sequence diversity, our work will inform future studies aimed at elucidating the function and mode of action of MAX effectors.

Molecular engineering of plant immune receptors for tailored crop disease resistance

The specific recognition of pathogen effectors by intracellular nucleotide-binding and leucine-rich repeat domain receptors (NLRs) is an important component of plant immunity. Creating NLRs with new bespoke recognition specificities is a major goal in molecular plant pathology as it promises to provide unlimited resources for the resistance of crops against diseases. Recent breakthrough discoveries on the structure and molecular activity of NLRs begin to enable their knowledge-guided molecular engineering. First, studies succeeded to extend or change effector recognition specificities by modifying, in a structure-guided manner, the NLR domains that directly bind effectors. By modifying the LRR domain of the singleton NLR Sr35 or the unconventional decoy domains of the helper NLRs RGA5 or Pik-1, receptors that detected other or additional effectors were created.

1H, 13C, 15 N backbone and side-chain NMR assignments for three MAX effectors from Magnaporthe oryzae

Effectors are small and very diverse proteins secreted by fungi and translocated in plant cells during infection. Among them, MAX effectors (for Magnaporthe Avrs and ToxB) were identified as a family of effectors that share an identical fold topology despite having highly divergent sequences. They are mostly secreted by ascomycetes from the Magnaporthe genus, a fungus that causes the rice blast, a plant disease leading to huge crop losses. As rice is the first source of calories in many countries, especially in Asia and Africa, this constitutes a threat for world food security. Hence, a better understanding of these effectors, including structural and functional characterization, constitutes a strategic milestone in the fight against phytopathogen fungi and may give clues for the development of resistant varieties of rice. We report here the near complete ¹H, ¹⁵ N and ¹³C NMR resonance assignment of three new putative MAX effectors (MAX47, MAX60 and MAX67). Secondary structure determination using TALOS-N and CSI.3 demonstrates a high content of β-strands in all the three proteins, in agreement with the canonic ß-sandwich structure of MAX effectors. This preliminary study provides foundations for further structural characterization, that will help in turn to improve sequence predictions of other MAX effectors through data mining.

Insight into the structure and molecular mode of action of plant paired NLR immune receptors

The specific recognition of pathogen effectors by intracellular nucleotide-binding domain and leucine-rich repeat receptors (NLRs) is an important component of plant immunity. NLRs have a conserved modular architecture and can be subdivided according to their signaling domain that is mostly a coiled-coil (CC) or a Toll/Interleukin1 receptor (TIR) domain into CNLs and TNLs. Single NLR proteins are often sufficient for both effector recognition and immune activation. However, sometimes, they act in pairs, where two different NLRs are required for disease resistance. Functional studies have revealed that in these cases one NLR of the pair acts as a sensor (sNLR) and one as a helper (hNLR). The genes corresponding to such resistance protein pairs with one-to-one functional co-dependence are clustered, generally with a head-to-head orientation and shared promoter sequences. sNLRs in such functional NLR pairs have additional, non-canonical and highly diverse domains integrated in their conserved modular architecture, which are thought to act as decoys to trap effectors. Recent structure-function studies on the Arabidopsis thaliana TNL pair RRS1/RPS4 and on the rice CNL pairs RGA4/RGA5 and Pik-1/Pik-2 are unraveling how such protein pairs function together. Focusing on these model NLR pairs and other recent examples, this review highlights the distinctive features of NLR pairs and their various fascinating mode of action in pathogen effector perception. We also discuss how these findings on NLR pairs pave the way toward improved plant disease resistance.

The activity of the RGA5 sensor NLR from rice requires binding of its integrated HMA domain to effectors but not HMA domain self-interaction

The rice nucleotide-binding (NB) and leucine-rich repeat (LRR) domain immune receptors (NLRs) RGA4 and RGA5 form a helper NLR/sensor NLR (hNLR/sNLR) pair that specifically recognizes the effectors AVR-Pia and AVR1-CO39 from the blast fungus Magnaporthe oryzae. While RGA4 contains only canonical NLR domains, RGA5 has an additional unconventional heavy metal-associated (HMA) domain integrated after its LRR domain. This RGA5HMA domain binds the effectors and is crucial for their recognition. Investigation of the three-dimensional structure of the AVR1-CO39/RGA5HMA complex by X-ray crystallography identified a candidate surface for effector binding in the HMA domain and showed that the HMA domain self-interacts in the absence of effector through the same surface. Here, we investigated the relevance of this HMA homodimerization for RGA5 function and the role of the RGA5HMA effector-binding and self-interaction surface in effector recognition. By analysing structure-informed point mutations in the RGA5HMA -binding surface in protein interaction studies and in Nicotiana benthamiana cell death assays, we found that HMA self-interaction does not contribute to RGA5 function. However, the effector-binding surface of RGA5HMA identified by X-ray crystallography is crucial for both in vitro and in vivo effector binding as well as effector recognition. These results support the current hypothesis that noncanonical integrated domains of NLRs act primarily as effector traps and deepen our understanding of the sNLRs' function within NLR pairs.

The stem rust effector protein AvrSr50 escapes Sr50 recognition by a substitution in a single surface-exposed residue

Pathogen effectors are crucial players during plant colonisation and infection. Plant resistance mostly relies on effector recognition to activate defence responses. Understanding how effector proteins escape from plant surveillance is important for plant breeding and resistance deployment. Here we examined the role of genetic diversity of the stem rust (Puccinia graminis f. sp. tritici (Pgt)) AvrSr50 gene in determining recognition by the corresponding wheat Sr50 resistance gene. We solved the crystal structure of a natural variant of AvrSr50 and used site-directed mutagenesis and transient expression assays to dissect the molecular mechanisms explaining gain of virulence. We report that AvrSr50 can escape recognition by Sr50 through different mechanisms including DNA insertion, stop codon loss or by amino-acid variation involving a single substitution of the AvrSr50 surface-exposed residue Q121. We also report structural homology of AvrSr50 to cupin superfamily members and carbohydrate-binding modules indicating a potential role in binding sugar moieties. This study identifies key polymorphic sites present in AvrSr50 alleles from natural stem rust populations that play important roles to escape from Sr50 recognition. This constitutes an important step to better understand Pgt effector evolution and to monitor AvrSr50 variants in natural rust populations.

New recognition specificity in a plant immune receptor by molecular engineering of its integrated domain

Plant nucleotide-binding and leucine-rich repeat domain proteins (NLRs) are immune sensors that recognize pathogen effectors. Here, we show that molecular engineering of the integrated decoy domain (ID) of an NLR can extend its recognition spectrum to a new effector. We relied for this on detailed knowledge on the recognition of the Magnaporthe oryzae effectors AVR-PikD, AVR-Pia, and AVR1-CO39 by, respectively, the rice NLRs Pikp-1 and RGA5. Both receptors detect their effectors through physical binding to their HMA (Heavy Metal-Associated) IDs. By introducing into RGA5_HMA the AVR-PikD binding residues of Pikp-1_HMA, we create a high-affinity binding surface for this effector. RGA5 variants carrying this engineered binding surface perceive the new ligand, AVR-PikD, and still recognize AVR-Pia and AVR1-CO39 in the model plant N. benthamiana. However, they do not confer extended disease resistance specificity against M. oryzae in transgenic rice plants. Altogether, our study provides a proof of concept for the design of new effector recognition specificities in NLRs through molecular engineering of IDs.

A novel robust and high-throughput method to measure cell death in Nicotiana benthamiana leaves by fluorescence imaging

Assessing immune responses and cell death in Nicotiana benthamiana leaf agro-infiltration assays is a powerful and widely used experimental approach in molecular plant pathology. Here, we describe a reliable high-throughput protocol to quantify strong, macroscopically visible cell death responses in N. benthamiana agro-infiltration assays. The method relies on measuring the reduction of leaf autofluorescence in the red spectrum upon cell death induction and provides quantitative data suitable for straightforward statistical analysis. Two different well-established model nucleotide-binding and leucine-rich repeat domain proteins (NLRs) were used to ensure the genericity of the approach. Its accuracy and versatility were compared to visual scoring of the cell death response and standard methods commonly used to characterize NLR activities in N. benthamiana. A discussion of the advantages and limitations of our method compared to other protocols demonstrates its robustness and versatility and provides an effective means to select the best-suited protocol for a defined experiment.

Precision Breeding Made Real with CRISPR: Illustration through Genetic Resistance to Pathogens

Since its discovery as a bacterial adaptive immune system and its development for genome editing in eukaryotes, the CRISPR technology has revolutionized plant research and precision crop breeding. The CRISPR toolbox holds great promise in the production of crops with genetic disease resistance to increase agriculture resilience and reduce chemical crop protection with a strong impact on the environment and public health. In this review, we provide an extensive overview on recent breakthroughs in CRISPR technology, including the newly developed prime editing system that allows precision gene editing in plants. We present how each CRISPR tool can be selected for optimal use in accordance with its specific strengths and limitations, and illustrate how the CRISPR toolbox can foster the development of genetically pathogen-resistant crops for sustainable agriculture.

SAT0280 IMPACT OF PLACENTAL FACTORS ON PREGNANCY AND FETAL OUTCOME IN SYSTEMIC SCLEROSIS

Background:

Systemic Sclerosis (SSc) is one of the rheumatic diseases burdened with obstetrical complications. An Italian multicenter study showed that women with SSc have a higher-than-normal risk of intrauterine growth restriction, preterm delivery, very-low birth weight babies and pregnancy should be discouraged in patients with severe organ damage. However, with a multidisciplinary management, patients with SSc can have successful outcomes1. Little is known about the pathogenesis of obstetrical complications, as studies on placenta are case reports or description of a few cases2,3.

Objectives:

The aim of this study was to analyze the placental alterations with a focus on the role of inflammation in the pathogenesis of obstetrical complications in SSc, including the study of the atypical chemokine receptor 2 (ACKR2), involved in immune modulation and known to be highly expressed in circulating leucocytes in SSc patients4-6.

Methods:

Eight SSc pregnant patients were compared with 16 patients with other rheumatic diseases (ORD) and 16 healthy controls (HC), matched for gestational age. Clinical data were collected. Placentas biopsies were obtained for histopathological analysis and immunohistochemistry for CD3, CD20, CD11c, CD68 and ACKR2. Frozen placenta samples from 4 SSc, 8 ORD and 8 HC were analyzed by qPCR for ACKR2 gene expression and proteins were extracted for multiplex assay for cytokines, chemokines and growth factors involved in angiogenesis and inflammation. Statistical analysis was performed with parametric or non-parametric tests depending on samples distribution.

Results:

The number of placental CD3 (p<0.05), CD68 (p<0.001) and CD11c+ (p<0.001) cells was significantly higher considering the group of patients affected by rheumatic diseases (SSc+ORD) compared to HC. The SSc group alone did not show significance due to the lower sample size. No differences were observed between groups in terms of vascular alterations or fibrosis. The percentage of stained area for ACKR2 and the ACKR2 transcripts levels were comparable between groups. Hepatocyte growth factor (HGF), involved in angiogenesis, was significantly increased in the group of rheumatic diseases patients (SSc+ORD) compared to HC (p<0.05), while the chemokine CCL5 was significantly higher in SSc patients compared to patients affected by ORD (p<0.05) and to HC (p<0.01). CCL5 levels directly correlated with the number of all inflammatory cells considered and higher levels were associated to histological villitis (p<0.01).

Conclusion:

The higher number of placental inflammatory cells and the alterations in the levels of HGF and especially CCL5 could play a role in the pathogenesis of the obstetrical complications in SSc. ACKR2 does not seem involved in the obstetrical complications of SSc.

References:

[1]Taraborelli M, et al. Arthritis Rheum. 2012

[2]Ibba-Manneschi L, et al. Ann Rheum Dis. 2010

[3]Doss BJ, et al. Hum Pathol. 1998

[4]Graham GJ. Eur J Immunol. 2009

[5]Martinez de la Torre Y, et al. Proc Natl Acad Sci U S A. 2007

[6]Codullo V, et al. Ann Rheum Dis. 2011

Disclosure of Interests:

None declared

Multiple strategies for pathogen perception by plant immune receptors

Contents Summary 17 I. Introduction 17 II. Pathogen perception by NLRs: from direct recognition to integrated decoys 18 III. Multiple activation and signaling pathways for NLRs 18 IV. How to engineer NLR-mediated disease resistance? 21 V. Conclusion 23 Acknowledgements 23 References 23 SUMMARY: Plants have evolved a complex immune system to protect themselves against phytopathogens. A major class of plant immune receptors called nucleotide-binding domain and leucine-rich repeat-containing proteins (NLRs) is ubiquitous in plants and is widely used for crop disease protection, making these proteins critical contributors to global food security. Until recently, NLRs were thought to be conserved in their modular architecture and functional features. Investigation of their biochemical, functional and structural properties has revealed fascinating mechanisms that enable these proteins to perceive a wide range of pathogens. Here, I review recent insights demonstrating that NLRs are more mechanistically and structurally diverse than previously thought. I also discuss how these findings provide exciting future prospects to improve plant disease resistance.

Recognition of the Magnaporthe oryzae Effector AVR-Pia by the Decoy Domain of the Rice NLR Immune Receptor RGA5

Nucleotide binding domain and leucine-rich repeat proteins (NLRs) are important receptors in plant immunity that allow recognition of pathogen effectors. The rice (Oryza sativa) NLR RGA5 recognizes the Magnaporthe oryzae effector AVR-Pia through direct interaction. Here, we gained detailed insights into the molecular and structural bases of AVR-Pia-RGA5 interaction and the role of the RATX1 decoy domain of RGA5. NMR titration combined with in vitro and in vivo protein-protein interaction analyses identified the AVR-Pia interaction surface that binds to the RATX1 domain. Structure-informed AVR-Pia mutants showed that, although AVR-Pia associates with additional sites in RGA5, binding to the RATX1 domain is necessary for pathogen recognition but can be of moderate affinity. Therefore, RGA5-mediated resistance is highly resilient to mutations in the effector. We propose a model that explains such robust effector recognition as a consequence, and an advantage, of the combination of integrated decoy domains with additional independent effector-NLR interactions.

Cytosolic activation of cell death and stem rust resistance by cereal MLA-family CC-NLR proteins

Plants possess intracellular immune receptors designated "nucleotide-binding domain and leucine-rich repeat" (NLR) proteins that translate pathogen-specific recognition into disease-resistance signaling. The wheat immune receptors Sr33 and Sr50 belong to the class of coiled-coil (CC) NLRs. They confer resistance against a broad spectrum of field isolates of Puccinia graminis f. sp. tritici, including the Ug99 lineage, and are homologs of the barley powdery mildew-resistance protein MLA10. Here, we show that, similarly to MLA10, the Sr33 and Sr50 CC domains are sufficient to induce cell death in Nicotiana benthamiana Autoactive CC domains and full-length Sr33 and Sr50 proteins self-associate in planta In contrast, truncated CC domains equivalent in size to an MLA10 fragment for which a crystal structure was previously determined fail to induce cell death and do not self-associate. Mutations in the truncated region also abolish self-association and cell-death signaling. Analysis of Sr33 and Sr50 CC domains fused to YFP and either nuclear localization or nuclear export signals in N benthamiana showed that cell-death induction occurs in the cytosol. In stable transgenic wheat plants, full-length Sr33 proteins targeted to the cytosol provided rust resistance, whereas nuclear-targeted Sr33 was not functional. These data are consistent with CC-mediated induction of both cell-death signaling and stem rust resistance in the cytosolic compartment, whereas previous research had suggested that MLA10-mediated cell-death and disease resistance signaling occur independently, in the cytosol and nucleus, respectively.

Placental lesions associated with oligohydramnios in fetal growth restricted (FGR) pregnancies

INTRODUCTION

Aim of the study was to investigate the association between placental pathology and oligohydramnios in pregnancies complicated by fetal growth restriction (FGR).

METHODS

Placentas from 221 consecutive FGR pregnancies and 63 healthy controls were studied. Pathological lesions were described according to consensus nomenclature and standardized criteria; both elementary lesions and constellations of lesions (patterns) were considered. Statistics included analysis of linear trends and multinomial logistic regression.

RESULTS

Amniotic fluid index (AFI) was normal in 56 (25.3%) FGR pregnancies, whereas mild, moderate and severe oligohydramnios were diagnosed in 32 (14.5%), 44 (19.9%) and 89 (40.3%) subjects, respectively. In FGR pregnancies, after adjustment for potential confounders, membrane meconium staining (chi-square = 28.6, p < 0.001), chronic villous hypoxia pattern (chi-square = 18.8, p < 0.001) and fetal thrombotic vasculopathy pattern (chi-square = 9.2, p = 0.002) were positively and linearly correlated to AFI decrease. Odds ratios of meconium and chronic villous hypoxia were 9.2 (95% CI = 2.6-32.9) and 4.2 (95% CI = 1.3-13.6) in FGR pregnancies with normal AFI and 25.2 (95% CI = 6.9-91.8) and 9.7 (95% CI = 3-31.5) in those with severe oligohydramnios (p = 0.005 and p = 0.023 compared to normal AFI, respectively).

DISCUSSION

In FGR pregnancies, reduction of amniotic fluid volume is directly correlated to histological features of placental under-perfusion, meconium staining of membranes and fetal vascular damage. These findings support the clinical notion that in FGR pregnancies oligohydramnios is a risk factor of fetal hypoxia and possibly of increased adverse neonatal outcomes.

A novel conserved mechanism for plant NLR protein pairs: the "integrated decoy" hypothesis

Plant immunity is often triggered by the specific recognition of pathogen effectors by intracellular nucleotide-binding, leucine-rich repeat receptors (NLR). Plant NLRs contain an N-terminal signaling domain that is mostly represented by either a Toll-interleukin1 receptor (TIR) domain or a coiled coil (CC) domain. In many cases, single NLR proteins are sufficient for both effector recognition and signaling activation. However, many paired NLRs have now been identified where both proteins are required to confer resistance to pathogens. Recent detailed studies on the Arabidopsis thaliana TIR-NLR pair RRS1 and RPS4 and on the rice CC-NLR pair RGA4 and RGA5 have revealed for the first time how such protein pairs function together. In both cases, the paired partners interact physically to form a hetero-complex receptor in which each partner plays distinct roles in effector recognition or signaling activation, highlighting a conserved mode of action of NLR pairs across both monocotyledonous and dicotyledonous plants. We also describe an "integrated decoy" model for the function of these receptor complexes. In this model, a plant protein targeted by an effector has been duplicated and fused to one member of the NLR pair, where it acts as a bait to trigger defense signaling by the second NLR upon effector binding. This mechanism may be common to many other plant NLR pairs.

A novel conserved mechanism for plant NLR protein pairs: the "integrated decoy" hypothesis

Plant immunity is often triggered by the specific recognition of pathogen effectors by intracellular nucleotide-binding, leucine-rich repeat receptors (NLR). Plant NLRs contain an N-terminal signaling domain that is mostly represented by either a Toll-interleukin1 receptor (TIR) domain or a coiled coil (CC) domain. In many cases, single NLR proteins are sufficient for both effector recognition and signaling activation. However, many paired NLRs have now been identified where both proteins are required to confer resistance to pathogens. Recent detailed studies on the Arabidopsis thaliana TIR-NLR pair RRS1 and RPS4 and on the rice CC-NLR pair RGA4 and RGA5 have revealed for the first time how such protein pairs function together. In both cases, the paired partners interact physically to form a hetero-complex receptor in which each partner plays distinct roles in effector recognition or signaling activation, highlighting a conserved mode of action of NLR pairs across both monocotyledonous and dicotyledonous plants. We also describe an "integrated decoy" model for the function of these receptor complexes. In this model, a plant protein targeted by an effector has been duplicated and fused to one member of the NLR pair, where it acts as a bait to trigger defense signaling by the second NLR upon effector binding. This mechanism may be common to many other plant NLR pairs.

The independent acquisition of plant root nitrogen-fixing symbiosis in Fabids recruited the same genetic pathway for nodule organogenesis

Only species belonging to the Fabid clade, limited to four classes and ten families of Angiosperms, are able to form nitrogen-fixing root nodule symbioses (RNS) with soil bacteria. This concerns plants of the legume family (Fabaceae) and Parasponia (Cannabaceae) associated with the Gram-negative proteobacteria collectively called rhizobia and actinorhizal plants associated with the Gram-positive actinomycetes of the genus Frankia. Calcium and calmodulin-dependent protein kinase (CCaMK) is a key component of the common signaling pathway leading to both rhizobial and arbuscular mycorrhizal symbioses (AM) and plays a central role in cross-signaling between root nodule organogenesis and infection processes. Here, we show that CCaMK is also needed for successful actinorhiza formation and interaction with AM fungi in the actinorhizal tree Casuarina glauca and is also able to restore both nodulation and AM symbioses in a Medicago truncatula ccamk mutant. Besides, we expressed auto-active CgCCaMK lacking the auto-inhibitory/CaM domain in two actinorhizal species: C. glauca (Casuarinaceae), which develops an intracellular infection pathway, and Discaria trinervis (Rhamnaceae) which is characterized by an ancestral intercellular infection mechanism. In both species, we found induction of nodulation independent of Frankia similar to response to the activation of CCaMK in the rhizobia-legume symbiosis and conclude that the regulation of actinorhiza organogenesis is conserved regardless of the infection mode. It has been suggested that rhizobial and actinorhizal symbioses originated from a common ancestor with several independent evolutionary origins. Our findings are consistent with the recruitment of a similar genetic pathway governing rhizobial and Frankia nodule organogenesis.

The rice resistance protein pair RGA4/RGA5 recognizes the Magnaporthe oryzae effectors AVR-Pia and AVR1-CO39 by direct binding

Resistance (R) proteins recognize pathogen avirulence (Avr) proteins by direct or indirect binding and are multidomain proteins generally carrying a nucleotide binding (NB) and a leucine-rich repeat (LRR) domain. Two NB-LRR protein-coding genes from rice (Oryza sativa), RGA4 and RGA5, were found to be required for the recognition of the Magnaporthe oryzae effector AVR1-CO39. RGA4 and RGA5 also mediate recognition of the unrelated M. oryzae effector AVR-Pia, indicating that the corresponding R proteins possess dual recognition specificity. For RGA5, two alternative transcripts, RGA5-A and RGA5-B, were identified. Genetic analysis showed that only RGA5-A confers resistance, while RGA5-B is inactive. Yeast two-hybrid, coimmunoprecipitation, and fluorescence resonance energy transfer-fluorescence lifetime imaging experiments revealed direct binding of AVR-Pia and AVR1-CO39 to RGA5-A, providing evidence for the recognition of multiple Avr proteins by direct binding to a single R protein. Direct binding seems to be required for resistance as an inactive AVR-Pia allele did not bind RGA5-A. A small Avr interaction domain with homology to the Avr recognition domain in the rice R protein Pik-1 was identified in the C terminus of RGA5-A. This reveals a mode of Avr protein recognition through direct binding to a novel, non-LRR interaction domain.

Placental cortisol and cord serum IGFBP-2 concentrations are important determinants of postnatal weight gain

There is a need to identify simple biochemical markers at birth that may predict subjects at risk of growth failure and metabolic complications in later life. Limited research to date has been performed on relationships of specific biochemical determinants at birth with postnatal weight gain and growth. We proposed to establish whether placental cortisol and IL-6 concentrations and cord serum IGF-II and IGFBP-2 concentrations influenced postnatal growth. We followed up from pregnancy 23 IUGR and 37 AGA subjects, and determined placental cortisol and IL-6 concentrations, and cord serum IGF-II, and IGFBP-2 concentrations at birth. We obtained height and weight measurements at 3, 6, 12, 24 months and 5 years of age in 20 IUGR and 15 AGA subjects of comparable gestational age. A multiple linear regression model was designed to establish the effect of the placental and cord serum peptides on postnatal linear growth and weight gain. All IUGR subjects had catch-up growth before 2 years of age. Placental cortisol concentration correlated positively with weight gain during the first 5 years of postnatal growth (P<0.05). Subjects with the highest placental cortisol concentrations were those who showed a greater increase in weight. Cord serum IGFBP-2 concentrations correlated positively with weight gain throughout the 5 year observation period (P:0.003). The subjects with the highest concentrations showed a greater weight gain. Placental cortisol and cord serum IGFBP-2 concentrations were related to postnatal weight gain, suggesting that the fetal environment has long-term effects on growth.

Unusual presentation of juvenile granulosa cell tumor of the ovary

BACKGROUND

We present a case report of juvenile granulosa cell tumor of the ovary (JGCT) with an unusual clinical presentation and hormonal secretion.

CASE

A 16-yr-old girl had developed spontaneous menarche at the age of 12 yr, but after this initial menstrual bleeding she had no further periods for 4 yr. She had no clinical signs of virilization. Endocrinological studies detected high levels of DHEA, 17 hydroxyprogesterone (17OH-P), insulin and PRL, an exaggerated DHEA response after ACTH stimulation, and low FSH and high LH values after GnRH. An ultrasound examination revealed an irregular structure and increased diameters of her right ovary, due to the presence of a cyst. Because exploratory laparoscopy revealed the presence of a right ovarian mass, her right ovary was removed. JGCT was diagnosed. Ten days after surgery, menstrual bleeding initiated. Endocrinological evaluation after the operation showed that 17OH-P, insulin and basal FSH and LH serum values had returned to normal, while DHEA levels had decreased to within the upper limit of the normal range. Only PRL levels remained unchanged.

CONCLUSION

Our patient presented some unusual characteristics. She did not have precocious puberty, but secondary amenorrhea. Hormonal secretion consisted mainly of androgens, even though clinical signs of virilization were not present.

Raysum reconstruction algorithm in MR cholangiopancreatography

Magnetic resonance cholangiopancreatography (MRCP) is a new, non-invasive imaging technique for the visualization of the biliary ducts. The presence of stones within the choledocus is easily detectable in source images. However, three-dimensional reconstructions using the maximum intensity pixel (or projection) algorithm (MIP) fail to reproduce accurately the eventual presence of filling defects or parietal irregularities due to biliary stones. We used the Raysum algorithm in addition to the MIP in evaluating MRCPs of twelve patients with known choledocolithiasis. A visualization of the stones was obtained in nine (75%) patients by using the Raysum while visualization was obtained in one patient by using MIP. No additional sequences are required, and the post-processing time takes only a few seconds. The Raysum reconstruction can be successfully associated to the MIP in the three-dimensional evaluation of biliary stones in MRCP.

[Cholangiopancreatography with magnetic resonance. Clinical use of a new "inversion-recovery" sequence]

This study was aimed at correlating the yield of a three-dimensional (3D) inversion-recovery (IR) turbo spin-echo MR cholangiopancreatography (MRCP) sequence with that of ERCP and PTC in the imaging of the normal and abnormal biliopancreatic tract. Thirty patients with suspected biliary and pancreatic diseases were examined with MRCP first and then with ERCP or PTC; they were also submitted to US, CT and conventional MR studies and in 5 of them CT cholangiography was also performed. Five patients were normal and 25 had various obstructive abnormalities: 5 patients had gallbladder stones, 8 common bile duct stones, 5 a cholangiocarcinoma and 7 an adenocarcinoma of the pancreatic head or papilla. MRCP was performed with a superconductive magnet at 0.5 T, with volumetric images on coronal planes acquired using an IR turbo SE sequence (TR 2500, TE 1000, TF 89, 4 NEX) with respiratory triggering and vascular presaturation. Segmental intrahepatic bile ducts were correctly depicted in all the patients with benign or malignant obstruction of the common bile duct, but with some respiratory artifacts. Common bile duct stones were correctly depicted in 7 of 8 patients, but studying also the single coronal slices. With this method, the stones were clearly demonstrated in 22 examined gallbladders. Neoplastic obstruction and the obstruction level were correctly identified in all patients. Pancreatic ducts were shown in normal patients and in 8 of 13 patients with neoplastic or lithiasic obstruction of the common bile duct mainly on the pancreatic head. ERCP was carried out successfully in 5 patients with common bile duct stones and in 7 patients with neoplastic obstruction; in the other cancer patients, PTC was necessary. To conclude, respiratory-triggered 3D IR turbo spin-echo MRCP is a noninvasive technique to study mostly biliary conditions which yields similar information to ERCP and PTC in a large number of patients. Moreover, this sequence can be used with midfield MR units to study the obstruction of the biliary and pancreatic ducts not only when invasive techniques fail, but also routinely.

The US,CT and MR findings of cubital bursitis: a report of five cases

OBJECTIVE

The purpose of the study was to evaluate the appearance of "cubital bursitis" on ultrasonography and CT and MR imaging. "Cubital bursitis" is a rare pathological condition involving a large swelling of the bicipito-radial or interosseous bursae located at the insertion of the distal biceps tendon on the radial tuberosity.

DESIGN AND PATIENTS

We report on five patients with "cubital bursitis" resulting from their work or sporting activities. All patients underwent an ultrasound and MR examination. CT scans were performed on two patients before and after contrast enhancement.

RESULTS

Ultrasound studies showed a fusiform anechoic or hypoechoic lesion. CT images showed the lesions but there were some difficulties in determining the exact extent of the bursae. MR imaging showed the enlarged bursae and their fluid content. Four patients each underwent a surgical procedure.

CONCLUSION

Ultrasound and CT were effective in the evaluation of "cubital bursitis", but with some diagnostic difficulties. MR imaging is probably the method of choice for determining both the development of the bursae and their fluid content.

Large lipomas of the colon: CT and MR findings in three symptomatic cases

We report on three patients with large lipomas in the wall of the cecum, causing intussusception. Endoscopy is the preferred modality for small lipomas, whereas CT and MR imaging are more useful in their ability in detecting fatty masses and assessing the location of lesions. Barium enema study may contribute to the preoperative planning in selected cases.

[Medial luxation of the long head of the brachial biceps. Magnetic resonance imaging]

The medial intraarticular dislocation of the biceps tendon of the shoulder is a rare pathologic condition and its diagnosis before surgery is very important to properly repair the tears of rotator cuff tendons, the rotator cuff being nearly always involved. We report our experience in 8 patients (1.8%) with biceps tendon dislocation observed in a series of 432 patients submitted to MR studies to address several diagnostic issues. The MR patterns of biceps tendon dislocation and the related physiopathologic mechanisms are discussed. The MR images were retrospectively reviewed by two of the authors and dislocations were diagnosed in a subgroup of 34 patients (7.8%), associated with full-thickness tears of the tendon of supraspinatus muscle; all patients also presented a full-thickness tear of the subscapularis tendon. A dislocated biceps tendon can follow a variety of courses depending on the pattern of subscapularis tendon tear. We always found a complete dislocation of the biceps tendon; other dislocation patterns reported in the literature, and particularly oblique and superficial dislocations, were never observed in our series. Dislocation is visible on axial images, where the tendon appears completely displaced from the bicipital groove, but also sagittal and coronal images can depict the more medial position of the tendon. In our patients this abnormality was correctly identified in 4 patients during the first observation and in the extant patients during the retrospective review. The dislocation of the biceps tendon of the shoulder was frequently associated with a complete tear of the supraspinatus tendon (23.5%). All patients exhibited severe joint effusion and in two patients the dislodged tendon was also inflamed.

Tailgut cysts: CT and MR findings

Two cases of tailgut cysts are reported. These lesions are rare and congenital, lying anterior to the sacrum and posterior to the rectum. CT findings are described. For one patient MR evidence is also presented. In a second case, the mass showed malignant behavior with local recurrence.

In vitro cytokine production and T-cell proliferation in patients undergoing cardiopulmonary by-pass

Cardiac surgery, employing cardiopulmonary by-pass (CPB), has long been associated with a generalized immunosuppression. To further understand the complex physiological and immunological changes related to CPB, we decided to investigate whether CPB affects the immune response, with regard to T-cell activation and cytokine production. Using phytohaemagglutinin (PHA) as mitogen and peripheral blood mononuclear cells (PBMC) isolated from patients undergoing CPB, we investigated whether this procedure has any effect on interferon-gamma(IFN-gamma) and other cytokine production and/or PBMC proliferation. Comparisons were made between the responsiveness of PBMC obtained before, during and at the end of CPB. In all patients, CPB significantly reduces IFN-gamma and interleukin 2 (IL-2) production in response to PHA. On the other hand, tumour necrosis factor-alpha (TNF-alpha) production was also significantly diminished, while interleukin 6 (IL-6), interleukin 1 beta (IL-1 beta) and interleukin 8 (IL-8) release in response to PHA was not significantly affected. Reduced IFN-gamma, IL-2 and TNF-alpha production was associated with a significant decrease in PBMC proliferation. These results might be related to the mechanical damage on blood cells described during extracorporeal circulation procedures as well as the release of immunosuppressive factors during surgery. The immunosuppression observed during CPB may play an important role in the development of infectious complications after CPB.

Effects of hypoxia on the cytotoxicity mediated by tumor necrosis factor-alpha

We investigated whether hypoxia (2% O2, approximately 14 mm Hg partial pressure) in comparison to O2 atmospheric pressure (20.9% O2, approximately 140 mm Hg) can affect the cytotoxic effects of tumor necrosis factor-alpha (TNF) on the murine cell line L929. Under hypoxic conditions, L929 cells were significantly less inhibited by TNF treatment, even in the presence of actinomycin D. Moreover, under hypoxic conditions, TNF cytotoxicity was significantly inhibited by glutathione, which has been shown to protect cells against oxidative damage induced by various agents. On the other hand, under aerobic conditions treatment with other antioxidant agents and active species oxygen scavengers, as superoxide dismutase and catalase, did not markedly affect the cytotoxicity of TNF. Since hypoxia occurs normally in most solid tumors, these results are interesting because they suggest a disadvantageous inhibition of the cytotoxic effects of TNF in vivo in hypoxic tissues and confirm that oxygen-dependent metabolic processes or free radicals are required to exert TNF-induced cytotoxicity.

[Radiopaque abdominal foreign bodies introduced by the enteral route. 4-year experience]

The aim of this work has been the comparison between the results found in literature and our experience with the introduction of radiopaque foreign bodies by enteral way into the abdomen. The kind of our patients, most of whom were in jail, the sufficient number of cases and the particularity of some of them have convinced us of the soundness of our experience and have persuaded us to briefly report it, with our observations and conclusions. The first thing we want to point out, on the basis of our study, is that the degree of radiopacity of a foreign body is more important than its dimensions as far as its visibility at X-ray examination is concerned. Another conclusive point we want to stress is that surgery is often needed to remove foreign bodies introduced by rectum, while most patients who ingest foreign bodies do not need surgery and expel what they have ingested, without complications, by rectal way.

[Preliminary observations, at the ultrastructural level, on the reactivity of cerebral arteries from New Zealand rabbits to combined atherogenic stimuli (hypercholesterol diet and hypertension)]

Both in monkeys (Rhesus and Cynomolgus) and in New Zealand rabbits fed an atherogenic diet, a marked delay in the appearance of atherosclerotic lesions of the cerebral arteries in comparison with other arterial districts has been observed. This appearance has been described in monkeys as relatively earlier if hypertension is added to the atherogenic diet. Preliminary observations on a little group of rabbits on a 3 months hypercholesterolic diet, subjected to Goldblatt aortic coarctation, have shown an increase of blood pressure and a severe gross atherosclerotic involvement of aorta, resembling the one obtainable after 6 months of atherogenic diet. Histologically, the aorta predominantly shows lesions of the fatty streaks type with necrotic areas in the deep; the carotid lesions show some lipid in smooth muscle cells disseminated in a sub-endothelial "edematous" space (rich in protein). The cerebral arteries do not show any lesion. At TEM, the aortic lesions look sometimes as advanced plaques with an initial fibrosis at the surface; the carotid lesions are characterized by a granular deposit in the sub-endothelial space in which some smooth muscle cells (with lipid in the cytoplasm) are present; in the cerebral arteries only the presence of collagen fibers among the smooth muscle cells of the media, never observed in the animals fed the atherogenic diet alone, has sometimes been noted.