Ribosome heterogeneity results in leader sequence-mediated regulation of protein synthesis in Francisella tularensis

Although ribosomes are generally examined in aggregate, ribosomes can be heterogenous in composition. Evidence is accumulating that changes in ribosome composition may result in altered function, such that ribosome heterogeneity may provide a mechanism to regulate protein synthesis. Ribosome heterogeneity in the human pathogen Francisella tularensis results from incorporation of one of three homologs of bS21, a small ribosomal subunit protein demonstrated to regulate protein synthesis in other bacteria. Loss of one homolog, bS21-2, results in genome-wide post-transcriptional changes in protein abundance. This suggests that bS21-2 can, either directly or indirectly, lead to preferential translation of particular mRNAs. Here, we examine the potential of bS21-2 to function in a leader sequence-dependent manner and to function indirectly, via Hfq. We found that the 5´ untranslated region (UTR) of some bS21-2-responsive genes, including key virulence genes, is sufficient to alter translation in cells lacking bS21-2. We further identify features of a 5´ UTR that allow responsiveness to bS21-2. These include an imperfect Shine-Dalgarno sequence and a particular six nucleotide sequence. Our results are consistent with a model in which a bS21 homolog increases the efficiency of translation initiation through interactions with specific leader sequences. With respect to bS21-2 indirectly regulating translation via the RNA-binding protein Hfq, we found that Hfq controls transcript abundance rather than protein synthesis, impacting virulence gene expression via a distinct mechanism. Together, we determined that ribosome composition in F. tularensis regulates translation in a leader sequence-dependent manner, a regulatory mechanism which may be used in other bacteria. IMPORTANCE Ribosome heterogeneity is common in bacteria, and there is mounting evidence that ribosome composition plays a regulatory role in protein synthesis. However, mechanisms of ribosome-driven gene regulation are not well understood. In the human pathogen Francisella tularensis, which encodes multiple homologs for the ribosomal protein bS21, loss of one homolog impacts protein synthesis and virulence. Here, we explore the mechanism behind bS21-mediated changes in protein synthesis, finding that they can be linked to altered translation initiation and are dependent on specific sequences in the leaders of transcripts. Our data support a model in which ribosome composition regulates gene expression through translation, a strategy that may be conserved in diverse organisms with various sources of ribosome heterogeneity.

Time-restricted feeding mitigates obesity through adipocyte thermogenesis

Misalignment of feeding rhythms with the light-dark cycle leads to disrupted peripheral circadian clocks and obesity. Conversely, restricting feeding to the active period mitigates metabolic syndrome through mechanisms that remain unknown. We found that genetic enhancement of adipocyte thermogenesis through ablation of the zinc finger protein 423 (ZFP423) attenuated obesity caused by consumption of a high-fat diet during the inactive (light) period by increasing futile creatine cycling in mice. Circadian control of adipocyte creatine metabolism underlies the timing of diet-induced thermogenesis, and enhancement of adipocyte circadian rhythms through overexpression of the clock activator brain and muscle Arnt-like protein-1 (BMAL1) ameliorated metabolic complications during diet-induced obesity. These findings uncover rhythmic creatine-mediated thermogenesis as an essential mechanism that drives metabolic benefits during time-restricted feeding.

A Ribosomal Protein Homolog Governs Gene Expression and Virulence in a Bacterial Pathogen

The molecular machine necessary for protein synthesis, the ribosome, is generally considered constitutively functioning and lacking any inherent regulatory capacity. Yet ribosomes are commonly heterogeneous in composition and the impact of ribosome heterogeneity on translation is not well understood. Here, we determined that changes in ribosome protein composition govern gene expression in the intracellular bacterial pathogen Francisella tularensis. F. tularensis encodes three distinct homologs for bS21, a ribosomal protein involved in translation initiation, and analysis of purified F. tularensis ribosomes revealed they are heterogeneous with respect to bS21. The loss of one homolog, bS21-2, resulted in significant changes to the cellular proteome unlinked to changes in the transcriptome. Among the reduced proteins were components of the type VI secretion system (T6SS), an essential virulence factor encoded by the Francisella Pathogenicity Island. Furthermore, loss of bS21-2 led to an intramacrophage growth defect. Although multiple bS21 homologs complemented the loss of bS21-2 with respect to T6SS protein abundance, bS21-2 was uniquely necessary for robust intramacrophage growth, suggesting bS21-2 modulates additional virulence gene(s) distinct from the T6SS. Our results indicate that ribosome composition in F. tularensis, either directly or indirectly, posttranscriptionally modulates gene expression and virulence. Our findings are consistent with a model in which bS21 homologs function as posttranscriptional regulators, allowing preferential translation of specific subsets of mRNAs, likely at the stage of translation initiation. This work also raises the possibility that bS21 in other organisms may function similarly and that ribosome heterogeneity may permit many bacteria to posttranscriptionally regulate gene expression. IMPORTANCE While bacterial ribosomes are commonly heterogeneous in composition (e.g., incorporating different homologs for a ribosomal protein), how heterogeneity impacts translation is unclear. We found that the intracellular human pathogen Francisella tularensis has heterogeneous ribosomes, incorporating one of three homologs for ribosomal protein bS21. Furthermore, one bS21 homolog posttranscriptionally governs the expression of the F. tularensis type VI secretion system, an essential virulence factor. This bS21 homolog is also uniquely important for robust intracellular growth. Our data support a model in which bS21 heterogeneity leads to modulation of translation, providing another source of posttranscriptional gene regulation. Regulation of translation by bS21, or other sources of ribosomal heterogeneity, may be a conserved mechanism to control gene expression across the bacterial phylogeny.

NADH inhibition of SIRT1 links energy state to transcription during time-restricted feeding

In mammals, circadian rhythms are entrained to the light cycle and drive daily oscillations in levels of NAD+, a cosubstrate of the class III histone deacetylase sirtuin 1 (SIRT1) that associates with clock transcription factors. Although NAD+ also participates in redox reactions, the extent to which NAD(H) couples nutrient state with circadian transcriptional cycles remains unknown. Here we show that nocturnal animals subjected to time-restricted feeding of a calorie-restricted diet (TRF-CR) only during night-time display reduced body temperature and elevated hepatic NADH during daytime. Genetic uncoupling of nutrient state from NADH redox state through transduction of the water-forming NADH oxidase from Lactobacillus brevis (LbNOX) increases daytime body temperature and blood and liver acyl-carnitines. LbNOX expression in TRF-CR mice induces oxidative gene networks controlled by brain and muscle Arnt-like protein 1 (BMAL1) and peroxisome proliferator-activated receptor alpha (PPARα) and suppresses amino acid catabolic pathways. Enzymatic analyses reveal that NADH inhibits SIRT1 in vitro, corresponding with reduced deacetylation of SIRT1 substrates during TRF-CR in vivo. Remarkably, Sirt1 liver nullizygous animals subjected to TRF-CR display persistent hypothermia even when NADH is oxidized by LbNOX. Our findings reveal that the hepatic NADH cycle links nutrient state to whole-body energetics through the rhythmic regulation of SIRT1.

Circadian NAD(P)(H) cycles in cell metabolism

Intrinsic circadian clocks are present in all forms of photosensitive life, enabling daily anticipation of the light/dark cycle and separation of energy storage and utilization cycles on a 24-h timescale. The core mechanism underlying circadian rhythmicity involves a cell-autonomous transcription/translation feedback loop that in turn drives rhythmic organismal physiology. In mammals, genetic studies have established that the core clock plays an essential role in maintaining metabolic health through actions within both brain pacemaker neurons and peripheral tissues and that disruption of the clock contributes to disease. Peripheral clocks, in turn, can be entrained by metabolic cues. In this review, we focus on the role of the nucleotide NAD(P)(H) and NAD⁺-dependent sirtuin deacetylases as integrators of circadian and metabolic cycles, as well as the implications for this interrelationship in healthful aging.

Improved transformation efficiency of group A Streptococcus by inactivation of a type I restriction modification system

Streptococcus pyogenes or group A Streptococcus (GAS) is a leading cause of bacterial pharyngitis, skin and soft tissue infections, life-threatening invasive infections, and the post-infectious autoimmune syndromes of acute rheumatic fever and post-streptococcal glomerulonephritis. Genetic manipulation of this important pathogen is complicated by resistance of the organism to genetic transformation. Very low transformation efficiency is attributed to recognition and degradation of introduced foreign DNA by a type I restriction-modification system encoded by the hsdRSM locus. DNA sequence analysis of this locus in ten GAS strains that had been previously transformed with an unrelated plasmid revealed that six of the ten harbored a spontaneous mutation in hsdR, S, or M. The mutations were all different, and at least five of the six were predicted to result in loss of function of the respective hsd gene product. The unexpected occurrence of such mutations in previously transformed isolates suggested that the process of transformation selects for spontaneous inactivating mutations in the Hsd system. We investigated the possibility of exploiting the increased transformability of hsd mutants by constructing a deletion mutation in hsdM in GAS strain 854, a clinical isolate representative of the globally dominant M1T1 clonal group. Mutant strain 854ΔhsdM exhibited a 5-fold increase in electrotransformation efficiency compared to the wild type parent strain and no obvious change in growth or off-target gene expression. We conclude that genetic transformation of GAS selects for spontaneous mutants in the hsdRSM restriction modification system. We propose that use of a defined hsdM mutant as a parent strain for genetic manipulation of GAS will enhance transformation efficiency and reduce the likelihood of selecting spontaneous hsd mutants with uncharacterized genotypes.

Control of a programmed cell death pathway in Pseudomonas aeruginosa by an antiterminator

In Pseudomonas aeruginosa the alp system encodes a programmed cell death pathway that is switched on in a subset of cells in response to DNA damage and is linked to the virulence of the organism. Here we show that the central regulator of this pathway, AlpA, exerts its effects by acting as an antiterminator rather than a transcription activator. In particular, we present evidence that AlpA positively regulates the alpBCDE cell lysis genes, as well as genes in a second newly identified target locus, by recognizing specific DNA sites within the promoter, then binding RNA polymerase directly and allowing it to bypass intrinsic terminators positioned downstream. AlpA thus functions in a mechanistically unusual manner to control the expression of virulence genes in this opportunistic pathogen.

Structural Basis for Virulence Activation of Francisella tularensis

The bacterium Francisella tularensis (Ft) is one of the most infectious agents known. Ft virulence is controlled by a unique combination of transcription regulators: the MglA-SspA heterodimer, PigR, and the stress signal, ppGpp. MglA-SspA assembles with the σ70-associated RNAP holoenzyme (RNAPσ70), forming a virulence-specialized polymerase. These factors activate Francisella pathogenicity island (FPI) gene expression, which is required for virulence, but the mechanism is unknown. Here we report FtRNAPσ70-promoter-DNA, FtRNAPσ70-(MglA-SspA)-promoter DNA, and FtRNAPσ70-(MglA-SspA)-ppGpp-PigR-promoter DNA cryo-EM structures. Structural and genetic analyses show MglA-SspA facilitates σ70 binding to DNA to regulate virulence and virulence-enhancing genes. Our Escherichia coli RNAPσ70-homodimeric EcSspA structure suggests this is a general SspA-transcription regulation mechanism. Strikingly, our FtRNAPσ70-(MglA-SspA)-ppGpp-PigR-DNA structure reveals ppGpp binding to MglA-SspA tethers PigR to promoters. PigR in turn recruits FtRNAP αCTDs to DNA UP elements. Thus, these studies unveil a unique mechanism for Ft pathogenesis involving a virulence-specialized RNAP that employs two (MglA-SspA)-based strategies to activate virulence genes.

Tn-Seq reveals hidden complexity in the utilization of host-derived glutathione in Francisella tularensis

Host-derived glutathione (GSH) is an essential source of cysteine for the intracellular pathogen Francisella tularensis. In a comprehensive transposon insertion sequencing screen, we identified several F. tularensis genes that play central and previously unappreciated roles in the utilization of GSH during the growth of the bacterium in macrophages. We show that one of these, a gene we named dptA, encodes a proton-dependent oligopeptide transporter that enables growth of the organism on the dipeptide Cys-Gly, a key breakdown product of GSH generated by the enzyme γ-glutamyltranspeptidase (GGT). Although GGT was thought to be the principal enzyme involved in GSH breakdown in F. tularensis, our screen identified a second enzyme, referred to as ChaC, that is also involved in the utilization of exogenous GSH. However, unlike GGT and DptA, we show that the importance of ChaC in supporting intramacrophage growth extends beyond cysteine acquisition. Taken together, our findings provide a compendium of F. tularensis genes required for intracellular growth and identify new players in the metabolism of GSH that could be attractive targets for therapeutic intervention.

NAD+ Controls Circadian Reprogramming through PER2 Nuclear Translocation to Counter Aging

Disrupted sleep-wake and molecular circadian rhythms are a feature of aging associated with metabolic disease and reduced levels of NAD⁺, yet whether changes in nucleotide metabolism control circadian behavioral and genomic rhythms remains unknown. Here, we reveal that supplementation with the NAD⁺ precursor nicotinamide riboside (NR) markedly reprograms metabolic and stress-response pathways that decline with aging through inhibition of the clock repressor PER2. NR enhances BMAL1 chromatin binding genome-wide through PER2^K680 deacetylation, which in turn primes PER2 phosphorylation within a domain that controls nuclear transport and stability and that is mutated in human advanced sleep phase syndrome. In old mice, dampened BMAL1 chromatin binding, transcriptional oscillations, mitochondrial respiration rhythms, and late evening activity are restored by NAD⁺ repletion to youthful levels with NR. These results reveal effects of NAD⁺ on metabolism and the circadian system with aging through the spatiotemporal control of the molecular clock.

Pervasive Targeting of Nascent Transcripts by Hfq

Hfq is an RNA chaperone and an important post-transcriptional regulator in bacteria. Using chromatin immunoprecipitation coupled with high-throughput DNA sequencing (ChIP-seq), we show that Hfq associates with hundreds of different regions of the Pseudomonas aeruginosa chromosome. These associations are abolished when transcription is inhibited, indicating that they reflect Hfq binding to transcripts during their synthesis. Analogous ChIP-seq analyses with the post-transcriptional regulator Crc reveal that it associates with many of the same nascent transcripts as Hfq, an activity we show is Hfq dependent. Our findings indicate that Hfq binds many transcripts co-transcriptionally in P. aeruginosa, often in concert with Crc, and uncover direct regulatory targets of these proteins. They also highlight a general approach for studying the interactions of RNA-binding proteins with nascent transcripts in bacteria. The binding of post-transcriptional regulators to nascent mRNAs may represent a prevalent means of controlling translation in bacteria where transcription and translation are coupled.

Secreted Effectors Encoded within and outside of the Francisella Pathogenicity Island Promote Intramacrophage Growth

The intracellular bacterial pathogen Francisella tularensis causes tularemia, a zoonosis that can be fatal. The type VI secretion system (T6SS) encoded by the Francisella pathogenicity island (FPI) is critical for the virulence of this organism. Existing studies suggest that the complete repertoire of T6SS effectors delivered to host cells is encoded by the FPI. Using a proteome-wide approach, we discovered that the FPI-encoded T6SS exports at least three effectors encoded outside of the island. These proteins share features with virulence determinants of other pathogens, and we provide evidence that they can contribute to intramacrophage growth. The remaining proteins that we identified are encoded within the FPI. Two of these FPI-encoded proteins constitute effectors, whereas the others form a unique complex required for core function of the T6SS apparatus. The discovery of secreted effectors mediating interactions between Francisella and its host significantly advances our understanding of the pathogenesis of this organism.

A response regulator promotes Francisella tularensis intramacrophage growth by repressing an anti-virulence factor

The orphan response regulator PmrA is essential for the intramacrophage growth and survival of Francisella tularensis. PmrA was thought to promote intramacrophage growth by binding directly to promoters on the Francisella Pathogenicity Island (FPI) and positively regulating the expression of FPI genes, which encode a Type VI secretion system required for intramacrophage growth. Using both ChIP-Seq and RNA-Seq we identify those regions of the F. tularensis chromosome occupied by PmrA and those genes that are regulated by PmrA. We find that PmrA associates with 252 distinct regions of the F. tularensis chromosome, but exerts regulatory effects at only a few of these locations. Rather than by functioning directly as an activator of FPI gene expression we present evidence that PmrA promotes intramacrophage growth by repressing the expression of a single target gene we refer to as priM (PmrA-repressed inhibitor of intramacrophage growth). Our findings thus indicate that the role of PmrA in facilitating intracellular growth is to repress a previously unknown anti-virulence factor. PriM is the first bacterially encoded factor to be described that can interfere with the intramacrophage growth and survival of F. tularensis.

Ubiquitous promoter-localization of essential virulence regulators in Francisella tularensis

Francisella tularensis is a Gram-negative bacterium whose ability to replicate within macrophages and cause disease is strictly dependent upon the coordinate activities of three transcription regulators called MglA, SspA, and PigR. MglA and SspA form a complex that associates with RNA polymerase (RNAP), whereas PigR is a putative DNA-binding protein that functions by contacting the MglA-SspA complex. Most transcription activators that bind the DNA are thought to occupy only those promoters whose activities they regulate. Here we show using chromatin immunoprecipitation coupled with high-throughput DNA sequencing (ChIP-Seq) that PigR, MglA, and SspA are found at virtually all promoters in F. tularensis and not just those of regulated genes. Furthermore, we find that the ability of PigR to associate with promoters is dependent upon the presence of MglA, suggesting that interaction with the RNAP-associated MglA-SspA complex is what directs PigR to promoters in F. tularensis. Finally, we present evidence that the ability of PigR (and thus MglA and SspA) to positively control the expression of genes is dictated by a specific 7 base pair sequence element that is present in the promoters of regulated genes. The three principal regulators of virulence gene expression in F. tularensis therefore function in a non-classical manner with PigR interacting with the RNAP-associated MglA-SspA complex at the majority of promoters but only activating transcription from those that contain a specific sequence element. Our findings reveal how transcription factors can exert regulatory effects at a restricted set of promoters despite being associated with most or all. This distinction between occupancy and regulatory effect uncovered by our data may be relevant to the study of RNAP-associated transcription regulators in other pathogenic bacteria.

Circadian regulation of cellular physiology

The circadian clock synchronizes behavioral and physiological processes on a daily basis in anticipation of the light-dark cycle. In mammals, molecular clocks are present in both the central pacemaker neurons and in nearly all peripheral tissues. Clock transcription factors in metabolic tissues coordinate metabolic fuel utilization and storage with alternating periods of feeding and fasting corresponding to the rest-activity cycle. In vitro and in vivo biochemical approaches have led to the discovery of mechanisms underlying the interplay between the molecular clock and the metabolic networks. For example, recent studies have demonstrated that the circadian clock controls rhythmic synthesis of the cofactor nicotinamide adenine dinucleotide (NAD(+)) and activity of NAD(+)-dependent sirtuin deacetylase enzymes to regulate mitochondrial function across the circadian cycle. In this chapter, we review current state-of-the-art methods to analyze circadian cycles in mitochondrial bioenergetics, glycolysis, and nucleotide metabolism in both cell-based and animal models.

Circadian clocks and metabolism

Circadian clocks maintain periodicity in internal cycles of behavior, physiology, and metabolism, enabling organisms to anticipate the 24-h rotation of the Earth. In mammals, circadian integration of metabolic systems optimizes energy harvesting and utilization across the light/dark cycle. Disruption of clock genes has recently been linked to sleep disorders and to the development of cardiometabolic disease. Conversely, aberrant nutrient signaling affects circadian rhythms of behavior. This chapter reviews the emerging relationship between the molecular clock and metabolic systems and examines evidence that circadian disruption exerts deleterious consequences on human health.

Nutrient sensing and the circadian clock

The circadian system synchronizes behavioral and physiologic processes with daily changes in the external light-dark cycle, optimizing energetic cycles with the rising and setting of the sun. Molecular clocks are organized hierarchically, with neural clocks orchestrating the daily switch between periods of feeding and fasting, and peripheral clocks generating 24h oscillations of energy storage and utilization. Recent studies indicate that clocks respond to nutrient signals and that a high-fat diet influences the period of locomotor activity under free-running conditions, a core property of the clock. A major goal is to identify the molecular basis for the reciprocal relation between metabolic and circadian pathways. Here the role of peptidergic hormones and macromolecules as nutrient signals integrating circadian and metabolic systems is highlighted.

Circadian clocks in fuel harvesting and energy homeostasis

Circadian systems have evolved in plants, eubacteria, neurospora, and the metazoa as a mechanism to optimize energy acquisition and storage in synchrony with the rotation of the Earth on its axis. In plants, circadian clocks drive the expression of genes involved in oxygenic photosynthesis during the light and nitrogen fixation during the dark, repeating this cycle each day. In mammals, the core clock in the suprachiasmatic nucleus (SCN) functions to entrain extra-SCN and peripheral clocks to the light cycle, including regions central to energy homeostasis and sleep, as well as peripheral tissues involved in glucose and lipid metabolism. Tissue-specific gene targeting has shown a primary role of clock genes in endocrine pancreas insulin secretion, indicating that local clocks play a cell-autonomous role in organismal homeostasis. A present focus is to dissect the consequences of clock disruption on modulation of nuclear hormone receptor signaling and on posttranscriptional regulation of intermediary metabolism. Experimental genetic studies have pointed toward extensive interplay between circadian and metabolic systems and offer a means to dissect the impact of local tissue molecular clocks on fuel utilization across the sleep-wake cycle.

Comparisons of risk factors for HIV-1 infection in Jefferson and Mobile County, Alabama

A study of the Alabama state AIDS database was conducted to determine whether differences exist in demographic and risk characteristics between patients with HIV-1 in Jefferson and Mobile County. The authors found that the age distribution of patients with HIV-1, the percent of those having AIDS, and the percent of those surviving were very similar. However, significant differences existed in patient-reported risk factors in the two counties. Homosexuality was reported as the major risk factor in both counties. However, there was proportionately more homosexuality reported in Jefferson County and, conversely, more heterosexuality reported in Mobile. There also were significant differences in race and gender distributions in the two counties. This was due in part to the proportionately higher prevalence of African American females of reproductive age with HIV-1 in Mobile County. This may pose a significantly greater risk for pediatric AIDS among African American females in Mobile County.

Recurrent non-0:1 Vibrio cholerae bacteremia in a patient with multiple myeloma

BACKGROUND

Episodes of bacteremia with non-0:1 Vibrio cholerae are rarely reported, even though the organism is endemic along the Gulf Coast of the United States. Recurrent episodes of bacteremia with non-0:1 V. cholerae are described even more rarely. A patient is reported who had multiple myeloma and experienced two episodes of bacteremia with non-0:1 V. cholerae.

METHODS

Hospital records and the medical literature were reviewed, and the organism was serotyped by the Alabama State Laboratory.

RESULTS

The patient had no prodromal illnesses or diarrhea with either episode of bacteremia. Treatment with empiric antibiotic therapy resulted in successful resolution of his bacteremia, which is fatal in almost 50% of reported cases in patients with malignant neoplasms.

CONCLUSIONS

This is the first reported case of non-0:1 V. cholerae bacteremia occurring in a patient with multiple myeloma. Both his initial episode and a second episode of bacteremia responded to broad-spectrum antibiotics, which are used as empiric therapy for patients with hematologic malignancies and fever. Emphasis is placed on the paucity of clinical manifestations and the need for empiric therapy for non-0:1 V. cholerae infection in patients with hematologic malignancies.

Human immunodeficiency virus infection elicits early antibody not detected by standard tests: implications for diagnostics and viral immunology

The FDA-approved tests for diagnosis of HIV exposure depend on detection of specific antibody in serum. HIV infection is missed in some individuals because they score seronegative by the standard clinical EIA and Western blot assays. This apparent immunological "silent" period following infection may last for months and has been reported to be as long as 3 years in rare cases. Is there truly a lack of an immune response or is there a more subtle, narrowly focused antibody response in these HIV-infected individuals which is not detected by the current tests? Using a nondenaturing serological assay (immunofluorescence of live infected T-cells), we found that each of four infected individuals "seronegative" by the standard tests did possess antibody against native HIV proteins expressed on infected cells. These antibodies reacting with native HIV antigenic epitopes were of the IgG isotype, they cross-reacted with many, but not all, of seven random HIV-1 isolates, and one of the sera immunoprecipitated HIV gp160 from NP-40-solubilized infected cells. These results show that seronegative, high-risk, infected individuals can actually be seropositive and that different types of assays using native antigenic epitopes may be required for screening. Implementation of these findings thus may decrease HIV transmission. These results also highlight the importance of protein conformation for many natural viral antigenic epitopes.

Viral pneumonias. A diagnostic and therapeutic challenge

Viral pneumonias are both a diagnostic and a therapeutic challenge for primary care physicians. The illness should be suspected when an upper respiratory tract infection progresses to include dyspnea and cyanosis. Rapid diagnostic tests are now available to detect most of the viruses that cause pneumonias. Fortunately, viral pneumonias usually resolve without specific antiviral therapy; however, ribavirin is indicated for respiratory syncytial virus pneumonia in children and ganciclovir sodium (Cytovene) for cytomegalovirus pneumonia in immunocompromised patients. Acyclovir (Zovirax) is indicated for pneumonias due to herpes simplex virus and varicella-zoster virus infections. A high index of suspicion for bacterial superinfections is essential to reduce the risk of death from this complication.

Heightened cutaneous reactions to mosquito bites in patients with acquired immunodeficiency syndrome receiving zidovudine

Three patients with acquired immunodeficiency syndrome noted changing cutaneous reactions to mosquito bites one to three months after starting zidovudine therapy. Enhanced T-cell function is one possibility for the heightened response to mosquito bites in these patients.

Role of marrow stromal cells in the establishment of a transformed lymphoblastic B-cell line from a normal human subject

A monoclonal human B-lymphoblastoid cell line (UTMB-460) arose spontaneously from the bone marrow of a normal healthy woman who was seropositive for an EB-virus infection. Chromosomally, the UTMB-460 cells are near tetraploid, with a specific translocation (8;9) (p11.2; p24), and have surface IgMk. The UTMB-460 cells are resistant to killing in vitro by spontaneous and rIFN alpha 2 and rIL-2 stimulated NK cells from the patient and other normal subjects, but are killed by lymphokine activated killer cells. The index patient has not developed leukemia/lymphoma during the follow-up interval of 22 months. The growth of UTMB-460 cells is supported by undefined growth factors in FCS and by BCGF in the absence of FCS. rIL-2 stimulates DNA synthesis by UTMB-460 cells. The UTMB-460 cells were adherent to the normal MSC in the primary culture and show specific heterotypic adherence to normal MSC when compared to skin fibroblasts. In addition, 6/6 normal marrow stromal cells and 4/6 normal skin fibroblasts induced growth of colonies from UTMB-460 cells. These data suggest that MSC interacted with the transformed cells (UTMB-460) in vitro and played a critical role in the establishment of the UTMB-460 cell line.

Comparative virulence and immunogenicity of the Towne strain and a nonattenuated strain of cytomegalovirus

The Towne strain cytomegalovirus and a low-passage strain, Toledo-1, were compared for virulence and immunogenicity in healthy adult male subjects to determine the suitability of the Towne strain for vaccination. Five seropositive subjects who received the Toledo-1 strain developed infections ranging in severity from laboratory abnormalities to mild mononucleosis syndromes (mean incubation, 4.7 weeks). None of the four seronegative subjects receiving the Towne strain developed systemic infection, but all developed delayed local reactions at the injection sites. All subjects developed cytotoxic lymphocyte responses specific to cytomegalovirus, usually HLA-restricted, but these were of greater magnitude and duration in the Toledo-1 recipients. The latter also developed natural killer cell and interferon responses, atypical lymphocytosis, inversion of helper/suppressor cell ratios, and depressed responses to T-cell mitogens, none of which occurred in Towne strain recipients. The results further substantiate the avirulence and immunogenicity of the Towne strain cytomegalovirus.

Decreased circulating large granular lymphocytes associated with depressed natural killer cell activity in renal transplant recipients

Renal transplant recipients (RTR) receiving prednisone and azathioprine (AZ) frequently have depressed natural killer (NK) cell activity. In humans, NK activity is mediated by the large granular lymphocyte (LGL). To determine the mechanism of depressed NK activity among RTR, we quantitated the NK activity of peripheral blood lymphocytes (PBL) and the percentage of circulating LGL in Giemsa-stained cytocentrifuge preparations of PBL from 20 RTR and 6 healthy volunteers. In addition, the PBL were incubated with 1000 U/ml IFN beta to assess augmentation of NK activity. Finally, single-cell cytotoxicity assays in agarose using highly purified LGL from our study subjects were performed to assess the ability of the LGL to bind and to kill the K562 target cells. Mean (+/- 1SD) NK activity at a 50:1 effector-to-target ratio using K562 targets was 51.2 +/- 21.8% among normals and 12.9 +/- 10.3% in RTR, and it was augmented to 60.5 +/- 13.1% and 17.5 +/- 10.3%, respectively, following interferon (IFN) exposure. Mean percentage of LGL among PBL in normals was 13.2 +/- 1.2%, and 4.0 +/- 1.7% in RTR. A significant correlation existed (R = 0.90) between NK activity and the numbers of LGL (P less than .001). In two patients, NK activity following cessation of azathioprine and prednisone increased significantly (P less than .005), and an increase of LGL from 6%-30% among PBL accompanied the increase in NK activity in one patient. Incubation with IFN boosted this patient's NK activity from 22% to 62%, suggesting the presence of circulating pre-NK cells among the LGL. There was no significant difference in the binding or killing of K562 targets by LGL in single-cell assays comparing RTR with normal controls (P greater than 0.1), indicating normal functioning LGL in our study subjects. These results indicate that decreased circulating LGL among RTR receiving AZ and prednisone is associated with depressed NK activity. The ability of IFN to augment the NK activity of RTR significantly suggests the presence of circulating pre-NK cells. Finally, the rebound of both the circulating number of LGL and the NK activity after cessation of immunosuppressive drugs suggests a direct effect of those drugs in the inhibition of NK in RTR.

Lymphokine-activated killer cell phenomenon. II. Precursor phenotype is serologically distinct from peripheral T lymphocytes, memory cytotoxic thymus-derived lymphocytes, and natural killer cells

Culture of human peripheral blood lymphocytes (PBL) in partially purified and lectin-free interleukin 2 results in the generation of cytotoxic effector cells which have the unique property of lysing natural killer (NK)-resistant fresh human tumor cells. We have termed these effector cells "lymphokine- activated killer" cells (LAK). LAK are generated from both normal and cancer patients' PBL and are able to lyse both autologous and allogeneic tumor cells from all histologic tumor types tested. Our previous studies suggested that the LAK phenomenon was distinct from either the cytotoxic thymus-derived lymphocyte (CTL) or NK systems based on a variety of criteria. This study reports that the cell type involved is also distinct, as determined by phenotypic characteristics. The LAK effector cell phenotype was analyzed in parallel with alloimmune CTL, and LAK were found to be similarly susceptible to the monoclonal anti-T cell antibodies OKT-3 or OKT-8 plus complement. In contrast the LAK precursor was not susceptible to the OKT-3 or Leu-1 antibodies plus complement, while the ability to generate alloimmune CTL was totally obliterated when tested using the same PBL responder population; in fact, generation of LAK was found to be augmented five- to sixfold, clearly suggesting that LAK precursor cells are not T lymphocytes as defined by these antibodies. LAK precursors were found to be abundant in NK cell-enriched Percoll gradient fractions, which had been depleted of the 29 degrees C E- rosetting "high affinity" T cells. However, LAK precursors were found to be distinct from the majority of NK cells since lysis of fresh PBL with the monoclonal antibodies OKM-1, Leu-7, or OKT-11 significantly depleted or totally eliminated NK activity, while subsequent activation of the remaining cells generated high levels of LAK and in some cases augmented levels of LAK. LAK precursors were found to be distributed in the thymus, bone marrow, spleen, lymph node, and thoracic duct in addition to the PBL. Therefore, while the cell(s) responsible for activation and expression of LAK activity have some common features with the classic T cell-mediated CTL and NK cell systems, the LAK precursor cells are clearly distinct as determined by phenotype analysis using monoclonal antibodies and complement, and at present must be classified as a "null" cell.