Integrated structure-based protein interface prediction.

BACKGROUND: Identifying protein interfaces can inform how proteins interact with their binding partners, uncover the regulatory mechanisms that control biological functions and guide the development of novel therapeutic agents. A variety of computational approaches have been developed for predicting a protein's interfacial residues from its known sequence and structure. Methods using the known three-dimensional structures of proteins can be template-based or template-free. Template-based methods have limited success in predicting interfaces when homologues with known complex structures are not available to use as templates. The prediction performance of template-free methods that only rely only upon proteins' intrinsic properties is limited by the amount of biologically relevant features that can be included in an interface prediction model. RESULTS: We describe the development of an integrated method for protein interface prediction (ISPIP) to explore the hypothesis that the efficacy of a computational prediction method of protein binding sites can be enhanced by using a combination of methods that rely on orthogonal structure-based properties of a query protein, combining and balancing both template-free and template-based features. ISPIP is a method that integrates these approaches through simple linear or logistic regression models and more complex decision tree models. On a diverse test set of 156 query proteins, ISPIP outperforms each of its individual classifiers in identifying protein binding interfaces. CONCLUSIONS: The integrated method captures the best performance of individual classifiers and delivers an improved interface prediction. The method is robust and performs well even when one of the individual classifiers performs poorly on a particular query protein. This work demonstrates that integrating orthogonal methods that depend on different structural properties of proteins performs better at interface prediction than any individual classifier alone.

Microwave tomography with phaseless data on the calcaneus by means of artificial neural networks.

The aim of this study is to use a multilayer perceptron (MLP) artificial neural network (ANN) for phaseless imaging the human heel (modeled as a bilayer dielectric media: bone and surrounding tissue) and the calcaneus cross-section size and location using a two-dimensional (2D) microwave tomographic array. Computer simulations were performed over 2D dielectric maps inspired by computed tomography (CT) images of human heels for training and testing the MLP. A morphometric analysis was performed to account for the scatterer shape influence on the results. A robustness analysis was also conducted in order to study the MLP performance in noisy conditions. The standard deviations of the relative percentage errors on estimating the dielectric properties of the calcaneus bone were relatively high. Regarding the calcaneus surrounding tissue, the dielectric parameters estimations are better, with relative percentage error standard deviations up to ≈ 15%. The location and size of the calcaneus are always properly estimated with absolute error standard deviations up to ≈ 3 mm. Microwave tomography of the calcaneus using phaseless data. Simulations were inspired in Computed Tomography images from real heels (above). Inverse problem was solved using Multilayer Perceptron Artificial Neural Network (below).

Activation of the focal adhesion kinase signaling pathway by structural alterations in the carboxyl-terminal region of c-Crk II.

The Crk II adaptor protein encodes an SH2/SH3-domain containing adaptor protein with an SH2-SH3-SH3 domain structure that transmits signals from tyrosine kinases. The two SH3 domains are separated by a 54 amino acid linker region, whose length is highly conserved in xenopus, chicken, and mamalian Crk II proteins. To gain a better understanding into the role of the C-terminal region of Crk, we generated a series of C-terminal SH3 domain and SH3 linker mutants and examined their role in tyrosine kinase pathways. Expression of point mutations in the C-terminal SH3 domain (W276K Crk), at the tyrosine phosphorylation site (Y222F Crk II), or truncation of the entire C-terminus (Crk I or Crk Delta242), all increased c-Abl binding to the N-terminal SH3 domain of Crk and, where relevant, increased Tyr(222) phosphorylation. Deletion analysis of c-Crk II also revealed the presence of a C-terminal segment important for trans-activation of FAK. Such mutants, Crk Delta255 or Crk Delta242 Extended Linker (Crk Delta242([EL])), characterized by a disruption in the SH3 linker/C-terminal SH3 boundary, induced robust hyperphosphorylation of focal adhesion kinase (FAK) on Tyr(397), hyperphosphorylation of focal adhesion proteins p130(cas) and paxillin and increased focal adhesion formation in NIH3T3 cells. The effects of Crk Delta242([EL]) could be abrogated by co-expression of dominant negative c-Src or the protein tyrosine phosphatase PTP-PEST, but not by dominant negative Abl. Our results suggest that the C-terminal region of Crk contains negative regulatory elements important for both Abl and FAK dependent signal pathways, and offers a paradigm for an autoinhibitory region in the SH3 linker/C-terminal SH3 domain.

Homology-based annotation yields 1,042 new candidate genes in the Drosophila melanogaster genome.

The approach to annotating a genome critically affects the number and accuracy of genes identified in the genome sequence. Genome annotation based on stringent gene identification is prone to underestimate the complement of genes encoded in a genome. In contrast, over-prediction of putative genes followed by exhaustive computational sequence, motif and structural homology search will find rarely expressed, possibly unique, new genes at the risk of including non-functional genes. We developed a two-stage approach that combines the merits of stringent genome annotation with the benefits of over-prediction. First we identify plausible genes regardless of matches with EST, cDNA or protein sequences from the organism (stage 1). In the second stage, proteins predicted from the plausible genes are compared at the protein level with EST, cDNA and protein sequences, and protein structures from other organisms (stage 2). Remote but biologically meaningful protein sequence or structure homologies provide supporting evidence for genuine genes. The method, applied to the Drosophila melanogaster genome, validated 1,042 novel candidate genes after filtering 19,410 plausible genes, of which 12,124 matched the original 13,601 annotated genes. This annotation strategy is applicable to genomes of all organisms, including human.

Phosphorylation of c-Crk II on the negative regulatory Tyr222 mediates nerve growth factor-induced cell spreading and morphogenesis.

The Crk family of adaptor proteins participate in diverse signaling pathways that regulate growth factor-induced proliferation, anchorage-dependent DNA synthesis, and cytoskeletal reorganization, important for cell adhesion and motility. Using kidney epithelial 293T cells for transient co-transfection studies and the nerve growth factor (NGF)-responsive PC12 cell line as a model system for neuronal morphogenesis, we demonstrate that the non-receptor tyrosine kinase c-Abl is an intermediary for NGF-inducible c-Crk II phosphorylation on the negative regulatory Tyr(222). Transient expression of a c-Crk II Tyr(222) point mutant (c-Crk Y222F) in 293T cells induces hyperphosphorylation of paxillin on Tyr(31) and enhances complex formation between c-Crk Y222F and paxillin as well as c-Crk Y222F and c-Abl, suggesting that c-Crk II Tyr(222) phosphorylation induces both the dissociation of the Crk SH2 domain from paxillin and the Crk SH3 domain from c-Abl. Interestingly, examination of the early kinetics of NGF stimulation in PC12 cells showed that c-Crk II Tyr(222) phosphorylation preceded paxillin Tyr(31) phosphorylation, followed by a transient initial dissociation of the c-Crk II paxillin complex. PC12 cells overexpressing c-Crk Y222F manifested a defect in cellular adhesion and neuritogenesis that led to detachment of cells from the extracellular matrix, thus demonstrating the biological significance of c-Crk II tyrosine phosphorylation in NGF-dependent morphogenesis. Whereas previous studies have shown that Crk SH2 binding to paxillin is critical for cell adhesion and migration, our data show that the phosphorylation cycle of c-Crk II determines its dynamic interaction with paxillin, thereby regulating turnover of multiprotein complexes, a critical aspect of cytoskeletal plasticity and actin dynamics.

v-Crk modulation of growth factor-induced PC12 cell differentiation involves the Src homology 2 domain of v-Crk and sustained activation of the Ras/mitogen-activated protein kinase pathway.

Nerve growth factor (NGF) and epidermal growth factor (EGF) elicit contrasting actions on PC12 pheochromocytoma cells; NGF causes neuronal differentiation, and EGF induces proliferation. However, ectopic expression of the Src homology 2 (SH2) and SH3-containing oncogenic adaptor protein v-Crk in PC12 cells results in EGF-inducible neuronal differentiation (Hempstead, B. L., Birge, R. B., Fajardo, J. E., Glassman, R., Mahadeo, D., Kraemer, R., and Hanafusa, H. (1994) Mol. Cell. Biol. 14, 1964-1971). Here we show that v-Crk complexes with both the tyrosine-phosphorylated EGF receptor and the Ras guanine nucleotide exchange factor SOS in PC12 cells and is involved in an pathway analogous to that of Grb2. Expression of v-Crk results in an enhanced and sustained activation of Ras and mitogen-activated protein (MAP) kinase following EGF or NGF stimulation, implying that v-Crk can couple divergent tyrosine kinase pathways to Ras. To investigate the causal relationship between EGF receptor binding, MAP kinase activation, and neurite outgrowth, we stably expressed two v-Crk SH2 point mutants, v-Crk(R273N) and v-Crk(H294R) in PC12 cells. Mutations within the SH2 domain of v-Crk block binding of v-Crk to the tyrosine phosphorylated EGF receptor, compromise v-Crk's ability to cause EGF-dependent neurite outgrowth, and act in a dominant negative manner for NGF-induced neurite outgrowth. However, the kinetics of MAP kinase activation in EGF- or NGF-treated v-Crk-(R273N)PC12 cells was comparable with that in v-CrkPC12 cells. These data are consistent with a model in which v-Crk regulates the strength of a tyrosine kinase signal leading to prolonged activation of Ras and MAP kinase. However, the experiments with the SH2 mutants suggest that sustained activation, by itself, may not be sufficient to switch the fate of v-CrkPC12 cells from proliferation toward differentiation.

Expression of the v-crk oncogene product in PC12 cells results in rapid differentiation by both nerve growth factor- and epidermal growth factor-dependent pathways.

The transforming gene of the avian sarcoma virus CT10 encodes a fusion protein (p47gag-crk or v-Crk) containing viral Gag sequences fused to cellular sequences consisting primarily of Src homology regions 2 and 3 (SH2 and SH3 sequences). Here we report a novel function of v-Crk in the mammalian pheochromocytoma cell line, PC12, whereby stable expression of v-Crk induces accelerated differentiation, as assessed by induction of neurites following nerve growth factor (NGF) or basic fibroblast growth factor (bFGF) treatment compared with the effect in native PC12 cells. Surprisingly, however, these cells also develop extensive neurite processes after epidermal growth factor (EGF) stimulation, an event which is not observed in native PC12 cells. Following EGF or NGF stimulation of the v-CrkPC12 cells, the v-Crk protein itself became tyrosine phosphorylated within 1 min. Moreover, in A431 cells or TrkA-PC12 cells, which overexpress EGF receptors and TrkA, respectively, a GST-CrkSH2 fusion protein was indeed capable of binding these receptors in a phosphotyrosine-dependent manner, suggesting that v-Crk can directly couple to receptor tyrosine kinase pathways in PC12 cells. In transformed fibroblasts, v-Crk binds to specific tyrosine-phosphorylated proteins of p130 and paxillin. Both of these proteins are also complexed to v-Crk in PC12 cells, as evidenced by their coprecipitation with v-Crk in detergent lysates, suggesting that common effector pathways may occur in both cell types. However, whereas PC12 cellular differentiation can occur solely by overexpression of the v-Src or oncogenic Ras proteins, that induced by v-Crk requires a growth factor stimulatory signal, possibility in a two-step process.

A 31-amino-acid N-terminal extension regulates c-Crk binding to tyrosine-phosphorylated proteins.

Overproduction of v-Crk, but not of c-Crk, in chicken embryo fibroblasts results in cell transformation. The transforming activity of v-Crk mutants correlates with their ability to cause increased tyrosine phosphorylation of specific cellular proteins, a property that depends on the binding of v-Crk to phosphotyrosine residues via its SH2 domain. In this study, proteins translated in rabbit reticulocyte lysates were used to analyze interactions between Crk derivatives and tyrosine-phosphorylated proteins, particularly the epidermal growth factor (EGF) receptor. The results demonstrate that the binding affinity of c-Crk is much lower than that of v-Crk, despite the fact that both proteins contain identical SH2 domains. Moreover, a 31-amino-acid N-terminal extension of c-Crk, resulting from upstream translational initiation at a CUG codon, significantly increases the ability of the resulting protein to bind to phosphotyrosine-containing proteins. Of those 31 amino acids, 24 can be found in the 27-amino-acid region between Gag and Crk sequences in v-Crk, and removal of this region results in a protein with lower affinity toward the EGF receptor. In addition, fusion of Gag to the amino terminus of c-Crk yields a protein with a binding activity that is lower than that of v-Crk but significantly higher than that of c-Crk without the fusion. These data suggest that sequences N terminal to the Crk SH2 regulate binding activity to tyrosine-phosphorylated proteins and that the amino acids encoded immediately 5' to the c-Crk initiator AUG specifically increase binding affinity. In contrast, deletion of one or two SH3 domains of c-Crk proteins did not change their affinity for the EGF receptor. These results were confirmed in vivo by using A431-derived cell lines overproducing either the chicken c-Crk protein or c-Crk with the 31-amino-acid N-terminal extension. Furthermore, the in vivo experiments suggest that binding of Crk proteins to the stimulated EGF receptor results in Crk phosphorylation and subsequent loss of binding affinity.

False-negative urine latex particle agglutination testing in neonates with group B streptococcal bacteremia. A function of improper test implementation?

Although blood cultures remain the most specific indicator of Group B streptococcus (GBS) sepsis, a potentially life-threatening infection in neonates, test results may not be available for 24 to 48 hours. Detection of GBS antigen in the urine by latex particle agglutination (LPA) may speed diagnosis. This study analyzed the sensitivity of the GBS urine LPA assay under clinical conditions. The urine of neonates with early-onset GBS bacteremia was analyzed for GBS antigen over a three-year period at six military medical centers. Overall, 53.5% (38/71) of infants with positive blood cultures had a positive urine LPA test. Only one medical center routinely followed manufacturer's recommendations to concentrate urine specimens before testing. These data suggest that the sensitivity for the urine LPA assay, when performed on unconcentrated urine, is lower than previously reported. Clinicians should insist that the laboratory maximize sensitivity by concentrating urine prior to GBS LPA testing.

Identification and characterization of a high-affinity interaction between v-Crk and tyrosine-phosphorylated paxillin in CT10-transformed fibroblasts.

The genome of avian sarcoma virus CT10 encodes a fusion protein in which viral Gag sequences are fused to cellular Crk sequences containing primarily Src homology 2 (SH2) and Src homology 3 (SH3) domains. Transformation of chicken embryo fibroblasts (CEF) with the Gag-Crk fusion protein results in the elevation of tyrosine phosphorylation on specific cellular proteins with molecular weights of 130,000, 110,000, and 70,000 (p130, p110, and p70, respectively), an event which has been correlated with cell transformation. In this study, we have identified the 70-kDa tyrosine-phosphorylated protein in CT10-transformed CEF (CT10-CEF) as paxillin, a cytoskeletal protein suggested to be important for organizing the focal adhesion. Tyrosine-phosphorylated paxillin was found to be complexed with v-Crk in vivo as evident from coimmunoprecipitation studies. Moreover, a bacterially expressed recombinant glutathione S-transferase (GST)-CrkSH2 fragment bound paxillin in vitro with a subnanomolar affinity, suggesting that the SH2 domain of v-Crk is sufficient for binding. Mapping of the sequence specificity of a GST-CrkSH2 fusion protein with a partially degenerate phosphopeptide library determined a motif consisting of pYDXP, and in competitive coprecipitation studies, an acetylated A(p)YDAPA hexapeptide was able to quantitatively inhibit the binding of GST-CrkSH2 to paxillin and p130, suggesting that it meets the minimal structural requirements necessary for the interaction of CrkSH2 with physiological targets. To investigate the mechanism by which v-Crk elevates the tyrosine phosphorylation of paxillin in vivo, we have treated normal CEF and CT10-CEF with sodium vanadate to inhibit protein tyrosine phosphatase activity. These data suggest that paxillin is involved in a highly dynamic kinase-phosphatase interplay in normal CEF and that v-Crk binding may interrupt this balance to increase the steady-state level of tyrosine phosphorylation. By contrast, the 130-kDa protein was not tyrosine phosphorylated upon vanadate treatment of normal CEF and only weakly affected in the CT10-CEF, suggesting that a different mechanism may be involved in its phosphorylation.

Antimicrobial treatment of occult bacteremia: a multicenter cooperative study.

This prospective multicenter study was conducted to define more clearly clinical and laboratory criteria that predict a strong probability of occult bacteremia and to evaluate the effect of empiric broad spectrum antimicrobial treatment of these children. Children 3 to 36 months old with fever > or = 40 degrees C (104 degrees F) or, > or = 39.5 degrees C (103 degrees F) with white blood cells (WBC) > or = 15 x 10(9)/liter, and no focus of infection had blood cultures obtained and were randomized to treatment with oral amoxicillin/potassium clavulanate or intramuscular ceftriaxone. Sixty of 519 (11.6%) study patients had positive blood cultures: Streptococcus pneumoniae, 51; Haemophilus influenzae b, 6; Neisseria meningitidis, 2; and Group B Streptococcus, 1. Subgroups of high risk were identified as fever > or = 39.5 degrees C and WBC > or = 15 x 10(9)/liter, 55 of 331 or 16.6% positive with increasing incidence of positive culture with increasing increments of degrees of leukocytosis to WBC > or = 30 x 10(9)/liter where 9 of 21 or 42.9% were positive. Subgroups of significantly lower risk were identified as fever > or = 39.5 degrees C and WBC < 15 x 10(9)/liter, 5 of 182 or 2.7% positive and those with WBC < 10 x 10(9)/liter, 0 of 99 or 0.0% positive. Children with positive cultures who received ceftriaxone were nearly all afebrile after 24 hours whereas a significant number who received amoxicillin/potassium clavulanate remained febrile. In the 459 culture-negative children more amoxicillin/potassium clavulanate-treated children developed diarrhea and had less improvement in clinical scores after 24 hours than ceftriaxone-treated children.(ABSTRACT TRUNCATED AT 250 WORDS)

Failure of intrapartum antibiotics to prevent culture-proved neonatal group B streptococcal sepsis.

Early-onset group B streptococci (GBS-EOS) sepsis may be prevented by intrapartum antibiotics administered for GBS maternal colonization, premature labor, or prolonged rupture of membranes. We sought to identify cases of neonatal GBS sepsis after apparent failure of intrapartum chemotherapy and to determine the factors associated with failure of intrapartum antibiotics in these cases. We identified 96 GBS blood culture-positive infants at five military medical centers from 1987 to 1990. Eighteen (18.7%) of these infants had mothers who had received intrapartum antibiotics; 16 of 18 cases were early-onset disease, 15 of which initially had symptoms at less than 1 hour of age. Two infants had late-onset disease develop at 3 weeks of age. At least one perinatal risk factor (prematurity, prolonged rupture of membranes > 12 hours, maternal fever) was present in each of the 16 cases. Indications for intrapartum antibiotics were suspected chorioamnionitis (13 cases), GBS colonization and prolonged rupture of membranes or prematurity (3), and GBS colonization alone (2). Maternal antibiotics included ampicillin (14 cases), cephadyl (1), vancomycin (1), clindamycin (1), and gentamicin alone (1). The median number of doses of ampicillin before delivery was 1 (range, 1 to 21), which was administered at a median of 4 hours (range, 1 to 84) before birth. The mean dose of ampicillin was 1.8 gm/dose (range, 1 to 2 gm/dose). Two of 16 (12.5%) infants with GBS-EOS died as a result of GBS sepsis. In our population of neonates with GBS-EOS, 18.4% (16 of 87) of the infants had positive blood cultures despite intrapartum antibiotics. Intrapartum antibiotics may fail to prevent GBS sepsis in a number of infants born to mothers colonized with GBS or to those with acute chorioamnionitis.

The SH2- and SH3-containing Nck protein transforms mammalian fibroblasts in the absence of elevated phosphotyrosine levels.

We have established the human nck sequence as a new oncogene. Nck encodes one SH2 and three SH3 domains, the Src homology motifs found in nonreceptor tyrosine kinases, Ras GTPase-activating protein, phosphatidylinositol 3-kinase, and phospholipase C-gamma. Overexpression of human nck in 3Y1 rat fibroblasts results in transformation as judged by alteration of cell morphology, colony formation in soft agar, and tumor formation in nude BALB/c mice. However, overexpression of nck does not induce detectable elevation of the phosphotyrosine content of specific proteins, as is observed for v-crk, another SH2/SH3-containing oncogene. Despite this fact, we demonstrate that Nck retains the ability to bind tyrosine phosphorylated proteins in vitro, using a fusion protein of Nck with glutathione-S-transferase (GST). Moreover, when incubated with lysates prepared from v-src-transformed 3Y1 cells or the nck-overexpressing cell lines, GST-Nck binds to both p60v-src and serine/threonine kinases, respectively. Although phosphotyrosine levels are not elevated in the nck-expressing fibroblasts, vanadate treatment of these cells results in a phosphotyrosine pattern that is altered from the parental 3Y1 pattern, suggestive of a perturbation of indigenous tyrosine kinase pathways. These results suggest the possibility that human nck induces transformation in 3Y1 fibroblasts by virtue of its altered affinity or specificity for the normal substrates of its rat homolog and that Nck may play a role in linking tyrosine and serine/threonine kinase pathways within the cell.

Tyrosine-phosphorylated epidermal growth factor receptor and cellular p130 provide high affinity binding substrates to analyze Crk-phosphotyrosine-dependent interactions in vitro.

The genome of CT10 avian sarcoma virus encodes a 47-kDa fusion protein that consists of viral gag sequences fused to a cell-derived sequence containing SH2 and SH3 domains (v-crk). Genetic and biochemical evidence suggests that v-Crk can induce transformation of chicken embryo fibroblasts by influencing the activity of cellular proteins involved in growth regulation. In this report, we have developed an in vitro microtiter assay to study the binding of bacterially expressed glutathione S-transferase-fusion proteins of v-Crk and its cellular homolog, c-Crk, to the phosphorylated epidermal growth factor receptor (EGFR). Competitive binding data are presented that compare the abilities of heterologous glutathione S-transferase-fusion proteins containing GAPSH2[N], AblSH2, SrcSH2, and PLC-gamma SH2[N] sequences to inhibit Crk binding. Results indicate that both full-length Crk and GAPSH2[N] bind the phosphorylated EGFR with high affinity and can quantitatively compete the binding of each other by competitive enzyme-linked immunosorbent assay. Binding of full-length Crk or the isolated SH2 domains of GAP or Abl resulted in a significant protection of phosphorylated EGFR against dephosphorylation by cellular phosphatase activity, but did not appear to stimulate the intrinsic tyrosine kinase activity of the EGFR. To extend these findings to p130, the major phosphotyrosine-containing protein in CT10-transformed cells, we utilized a nitrocellulose filter binding assay. Results demonstrate high affinity binding of Crk toward denatured p130 and, as is the case for phosphorylated EGFR, Crk binding can partially protect p130 from phosphatase activity. However, no apparent competition of Crk binding was noted with heterologous SH2-containing proteins including GAPSH2[N], suggesting a possible specificity of Crk-p130 binding. These data are consistent with a direct role of SH2 in the modulation of cellular phosphotyrosine status in vivo.

Translation of bicistronic viral mRNA in transfected cells: regulation at the level of elongation.

The S1 species of mammalian reovirus mRNA, like a number of other viral but not cellular mRNAs, codes for two dissimilar polypeptides by initiation of translation at two 5'-proximal, out-of-frame AUG codons. To determine if uninfected cells can utilize bicistronic genes, a bovine papilloma virus-based vector system was used to select mouse C127 cell lines containing multiple integrated copies of the reovirus S1 gene. These cell lines produced both reovirus polypeptides from a single mRNA. In addition, studies of COS cells transfected with the S1 gene containing small changes around the first AUG suggest that bicistronic mRNA translation is regulated at the level of elongation. A model is proposed in which ribosomes engaged in translation of one reading frame interfere with movement of ribosomes in the other frame because of differences in codon usage. Expression of bicistronic genes may be similarly regulated in virus-infected cells.

Effects of elongation on the translation of a reovirus bicistronic mRNA.

The S1 species of reovirus mRNA contains two overlapping open reading frames. Both are utilized in either virus-infected or S1 DNA transfected mammalian cells, resulting in two different polypeptides from a single mRNA. Consistent with ribosome scanning, expression of the downstream reading frame was increased by sequence changes that diminished the consensus around the upstream initiator site. However, the upstream product was not decreased by the same changes, suggesting that its synthesis is rate-limited at elongation. The results suggest a model for regulating bicistronic mRNA translation in which the ribosomes in one reading frame interfere with the movement of ribosomes in the other frame due to different rates of elongation.

Tropical splenomegaly syndrome associated with cytomegalovirus infection.

The tropical splenomegaly syndrome (TSS) is characterized by massive splenomegaly with hypersplenism, moderate hepatomegaly, and lymphocytic infiltration of the hepatic sinusoids. In previous reports this syndrome has been shown to be a consequence of a disordered immunologic response of the host to malarial infection. Treatment with antimalarial drugs has resulted in a decrease in malarial antibody titers and a reduction in splenic size. We report a child who had TSS associated with cytomegalovirus infection rather than malaria. Our results suggest that TSS may be precipitated by a variety of infections producing chronic antigenic stimulation and perhaps by autoantigenic stimulation as well.

Inappropriate antidiuretic hormone in children with viral meningitis.

Urinary excretion rates of antidiuretic hormone were determined by radioimmunoassay in children with bacterial (6) and viral (11) meningitis, and in children with other febrile illnesses (7). These values were compared to normal data obtained from 50 healthy, normally hydrated children ranging in age from 1 week to 9 years. Plasma sodium concentrations were measured in the sick children; urine osmolality and creatinine concentrations were measured in all children. Upon admission, all children with bacterial meningitis and 64% of those with viral meningitis had urinary antidiuretic hormone excretion rates greater than 2 S.D. above values obtained from age-matched controls. Fifty-seven percent of children with other febrile illnesses had similarly elevated antidiuretic hormone values; however, only in the bacterial and viral meningitis groups were antidiuretic hormone excretion rates inappropriate because they occurred when serum sodium concentrations were found to be normal or low normal (i.e., 136 +/- 2 mEq/L and 137 +/- 1 mEq/L, respectively). The average serum sodium in the group with other febrile illnesses was higher (146 +/- 5 mEq/L; p less than 0.05) and could represent an appropriate stimulus for antidiuretic hormone release. In spite of high levels of antidiuretic hormone, most viral meningitis patients did not concentrate their urine, probably because all except 2 were younger than 2 months of age. We conclude that viral meningitis, like bacterial meningitis, frequently is associated with inappropriate antidiuretic hormone secretion; however, most children with viral meningitis may be protected from developing hyponatremia because of their inability to concentrate their urine.

Pleural empyema in children: a nationwide retrospective study.

Military hospitals across the United States provided data for this study on pediatric patients with pleural empyema. Haemophilus influenzae type b (17%), Streptococcus pneumoniae (14%), and Staphylococcus aureus (11%) were the most common etiologic agents. Male patients predominated, except among blacks. The mortality was high in patients with hospital-acquired empyemas.