Current Practices Supporting Rigid Bronchoscopy-An International Survey

BACKGROUND

There are no guidelines for anesthesia or staff support needed during rigid bronchoscopy (RB). Identifying current practice patterns for RB pertinent to anesthesia, multidisciplinary teams, and algorithms of intra and post-procedural care may inform best practice recommendations.

METHODS

Thirty-three-question survey created obtaining practice patterns for RB, disseminated via email to the members of the American Association of Bronchology and Interventional Pulmonology and the American College of Chest Physicians Interventional Chest Diagnostic Procedures Network.

RESULTS

One hundred seventy-five clinicians participated. Presence of a dedicated interventional pulmonology (IP) suite correlated with having a dedicated multidisciplinary RB team ( P =0.0001) and predicted higher likelihood of implementing team-based algorithms for managing complications (39.4% vs. 23.5%, P =0.024). A dedicated anesthesiology team was associated with the increased use of high-frequency jet ventilation ( P =0.0033), higher likelihood of laryngeal mask airway use post-RB extubation ( P =0.0249), and perceived lower rates of postprocedural anesthesia adverse effects ( P =0.0170). Although total intravenous anesthesia was the most used technique during RB (94.29%), significant variability in the modes of ventilation and administration of muscle relaxants was reported. Higher comfort levels in performing RB are reported for both anesthesiologists ( P =0.0074) and interventional pulmonologists ( P =0.05) with the presence of dedicated anesthesia and RB supportive teams, respectively.

CONCLUSION

Interventional bronchoscopists value dedicated services supporting RB. Multidisciplinary dedicated RB teams are more likely to implement protocols guiding management of intraprocedural complications. There are no preferred modes of ventilation during RB. These findings may guide future research on RB practices.

Safety and Efficacy of Manual Aspiration Via Small Bore Chest Tube in Facilitating the Outpatient Management of Transbronchial Biopsy-related Iatrogenic Pneumothorax

BACKGROUND

Iatrogenic pneumothorax complicates transbronchial biopsies with a prevalence of 1% to 6%. Conventional treatment consists of inpatient management with chest tube drainage. While aspiration techniques have been investigated in the management of both primary spontaneous and transthoracic lung biopsy-induced pneumothorax, its role in the management of transbronchial biopsy-iatrogenic pneumothorax (TBBX-IP) is undefined. An appealing treatment alternative for TBBX-IP may exist in the placement of a small bore chest tube (SBCT) followed by a manual aspiration (MA) technique promoting earlier SBCT removal to facilitate outpatient management. To our knowledge, no study exists evaluating the efficacy of MA via a SBCT performed specifically for TBBX-IP.

PATIENTS AND METHODS

Prospective evaluation of the efficacy of a protocolized pathway incorporating MA through a SBCT for the outpatient management of TBBX-IP. Primary outcome was the clinicoradiographic resolution of TBBX-IP avoiding hospitalizations.

RESULTS

A total of 763 biopsies performed; 31 complicated by TBBX-IP, 18 qualified for intervention. Sixteen were outpatients, 2 inpatients. Thirteen (81.25%) of the 16 outpatients were successfully treated with MA via SBCT and did not require admission. Twelve (75%) of these 13 had SBCT removed, 1 patient was discharged with SBCT and removed in 24 hours. Of the 18 patients requiring intervention, 13 (72.2%) were successfully treated with MA via SBCT enabling removal of SBCT. No patient required reintervention.

CONCLUSION

MA via SBCT represents a safe and viable management approach of TBBX-IP promoting earlier SBCT removal and decreased hospitalizations. Our results challenge conventional management of TBBX-IP warranting further investigation.

Dysfunctional HIV-specific CD8+ T cell proliferation is associated with increased caspase-8 activity and mediated by necroptosis

Decreased HIV-specific CD8(+) T cell proliferation is a hallmark of chronic infection, but the mechanisms of decline are unclear. We analyzed gene expression profiles from antigen-stimulated HIV-specific CD8(+) T cells from patients with controlled and uncontrolled infection and identified caspase-8 as a correlate of dysfunctional CD8(+) T cell proliferation. Caspase-8 activity was upregulated in HIV-specific CD8(+) T cells from progressors and correlated positively with disease progression and programmed cell death-1 (PD-1) expression, but negatively with proliferation. In addition, progressor cells displayed a decreased ability to upregulate membrane-associated caspase-8 activity and increased necrotic cell death following antigenic stimulation, implicating the programmed cell death pathway necroptosis. In vitro necroptosis blockade rescued HIV-specific CD8(+) T cell proliferation in progressors, as did silencing of necroptosis mediator RIPK3. Thus, chronic stimulation leading to upregulated caspase-8 activity contributes to dysfunctional HIV-specific CD8(+) T cell proliferation through activation of necroptosis and increased cell death.

Nkx2-5 activity is essential for cardiomyogenesis

The homeobox transcription factor tinman is essential for heart vessel formation in Drosophila. In contrast, mice lacking the murine homologue Nkx2-5 are defective in cardiac looping but not in cardiac myocyte development. The lack of an essential role for Nkx2-5 in cardiomyogenesis in mammalian systems is most likely the result of genetic redundancy with family members. In this study, we used a dominant negative mutant of Nkx2-5, created by fusing the repressor domain of engrailed 2 to the Nkx2-5 homeodomain, termed Nkx/EnR. Expression of Nkx/EnR inhibited Me(2)SO-induced cardiomyogenesis in P19 cells but not skeletal myogenesis. Nkx/EnR inhibited expression of cardiomyoblast markers, such as GATA-4 and MEF2C, but not of mesoderm markers, such as Brachyury T and Wnt5b, or of skeletal lineage markers, such as MyoD and Mox1. To identify the minimal region of Nkx2-5 that can trigger cardiomyogenesis, we analyzed the activity of various Nkx2-5 deletion mutants. The C-terminal domain was not necessary for the ability of Nkx2-5 to induce cardiomyogenesis and loss of this domain did not enhance myogenesis. Therefore, Nkx2-5 function is essential for commitment of mesoderm into the cardiac muscle lineage, and the N-terminal region, together with the homeodomain, is sufficient for cardiomyogenesis in P19 cells.

Wnt signaling regulates the function of MyoD and myogenin

The myogenic regulatory factors (MRFs), MyoD and myogenin, can induce myogenesis in a variety of cell lines but not efficiently in monolayer cultures of P19 embryonal carcinoma stem cells. Aggregation of cells expressing MRFs, termed P19[MRF] cells, results in an approximately 30-fold enhancement of myogenesis. Here we examine molecular events occurring during P19 cell aggregation to identify potential mechanisms regulating MRF activity. Although myogenin protein was continually present in the nuclei of >90% of P19[myogenin] cells, only a fraction of these cells differentiated. Consequently, it appears that post-translational regulation controls myogenin activity in a cell lineage-specific manner. A correlation was obtained between the expression of factors involved in somite patterning, including Wnt3a, Wnt5b, BMP-2/4, and Pax3, and the induction of myogenesis. Co-culturing P19[Wnt3a] cells with P19[MRF] cells in monolayer resulted in a 5- to 8-fold increase in myogenesis. Neither BMP-4 nor Pax3 was efficient in enhancing MRF activity in unaggregated P19 cultures. Furthermore, BMP-4 abrogated the enhanced myogenesis induced by Wnt signaling. Consequently, signaling events resulting from Wnt3a expression but not BMP-4 signaling or Pax3 expression, regulate MRF function. Therefore, the P19 cell culture system can be used to study the link between somite patterning events and myogenesis.

Myocyte enhancer factor 2C upregulates MASH-1 expression and induces neurogenesis in P19 cells

MEF2C is a transcription factor expressed in neural lineages. After transient transfection, the MEF2 family of factors can act synergistically with the neural-specific transcription factor, MASH-1, and activate exogenous neural-specific promoters. To determine whether MEF2C is capable of modulating endogenous gene expression, P19 cell lines were analyzed that overexpressed MEF2C, termed P19[MEF2C] cells. Here we show that P19[MEF2C] cells differentiate into neurons when aggregated with ME(2)SO. MEF2C-induced neurons expressed neurofilament protein, the nuclear antigen NeuN, as well as MASH-1. Our results indicate that MEF2C can directly or indirectly activate the expression of MASH-1, leading to neurogenesis.

Myocyte enhancer factor 2C and myogenin up-regulate each other's expression and induce the development of skeletal muscle in P19 cells

Two families of transcription factors, myogenic regulatory factors (MRFs) and myocyte enhancer factor 2 (MEF2), function synergistically to regulate myogenesis. In addition to activating structural muscle-specific genes, MRFs and MEF2 activate each other's expression. The MRF, myogenin, can activate MEF2 DNA binding activity when transfected into fibroblasts and, in turn, the myogenin promoter contains essential MEF2 DNA binding elements. To determine which MEF2 is involved in this regulation, P19 cells stably expressing MyoD and myogenin were compared for their ability to activate the expression of MEF2 family members. There was very little cross-activation of MyoD expression by myogenin and vice versa. Myogenin expression, and not MyoD, was found to up-regulate MEF2C expression. MEF2A, -B, and -D expression levels were not up-regulated by overexpression of either MyoD or myogenin. To examine whether MEF2C can differentially regulate MyoD or myogenin expression, P19 cell lines overexpressing MEF2C were analyzed. MEF2C induced myogenesis in P19 cells and up-regulated the expression of myogenin with 25-fold greater efficiency than that of MyoD. Therefore, myogenin and MEF2C participate in a regulatory loop in differentiating stem cells. This positive regulation does not extend to MyoD or the other MEF2 family members. Consequently, MEF2C appears to play a specific role in early events of myogenesis.

A polymerase chain reaction screening strategy for the promoter of the canine dystrophin gene

OBJECTIVE

To develop a polymerase chain reaction (PCR) strategy to screen the dystrophin promoter(s) in dogs with cardiac and skeletal myopathies.

ANIMALS

9 Doberman Pinschers, 1 Dalmation, and 1 Saint Bernard with dilated cardiomyopathy (DCM); 1 Irish Terrier with muscular dystrophy; and 2 dystrophin-deficient German Shorthaired Pointers (GSHP).

PROCEDURE

For each of the 3 unique exons associated with the muscle (M), Purkinje (P), and cortical (C) promoters of the dystrophin gene, each first exon, and the M promoter plus its first exon, were amplified, cloned, and sequenced. The M dystrophin transcript was amplified by reverse transcriptase PCR from skeletal and cardiac muscle RNA of 1 Doberman Pinscher and from skeletal muscle RNA of 1 GSHP.

RESULTS

The M, P, and C first exons were amplified from all dogs except the 2 GSHP, which had a deletion encompassing the entire M, P, and C dystrophin promoter region. The M transcript could not be amplified from muscles of the GSHP, but was amplified from skeletal and cardiac muscle of the Doberman Pinscher. Sequencing of the product representing the M promoter and its first exon revealed no differences between clinically normal dogs and the Doberman Pinscher with DCM.

CONCLUSIONS AND CLINICAL RELEVANCE

We have ruled out a major rearrangement of the dystrophin promoter region as the universal cause of DCM in Doberman Pinschers or of Irish Terrier myopathy. Use of the strategy identified a large deletion of this region in muscle from the GSHP.

Butyrycholinesterase K variant and Alzheimer's disease

This study attempted to corroborate findings on the association between butyrylcholinesterase K variant and Alzheimer's disease. This was performed on an autopsy-confirmed series of patients with Alzheimer's disease and controls. The butyrylcholinesterase K variant was found to be of increased allele frequency in patients with sporadic Alzheimer's disease. When related to APOE epsilon4 typing the association was specific but not sensitive for the diagnosis of Alzheimer's disease.

Myocyte enhancer factor 2C and Nkx2-5 up-regulate each other's expression and initiate cardiomyogenesis in P19 cells

The Nkx2-5 homeodomain protein plays a key role in cardiomyogenesis. Ectopic expression in frog and zebrafish embryos results in an enlarged myocardium; however, expression of Nkx2-5 in fibroblasts was not able to trigger the development of beating cardiac muscle. In order to examine the ability of Nkx2-5 to modulate endogenous cardiac specific gene expression in cells undergoing early stages of differentiation, P19 cell lines overexpressing Nkx2-5 were differentiated in the absence of Me2SO. Nkx2-5 expression induced cardiomyogenesis in these cultures aggregated without Me2SO. During differentiation into cardiac muscle, Nkx2-5 expression resulted in the activation of myocyte enhancer factor 2C (MEF2C), but not MEF2A, -B, or -D. In order to compare the abilities of Nkx2-5 and MEF2C to induce cellular differentiation, P19 cells overexpressing MEF2C were aggregated in the absence of Me2SO. Similar to Nkx2-5, MEF2C expression initiated cardiomyogenesis, resulting in the up-regulation of Brachyury T, bone morphogenetic protein-4, Nkx2-5, GATA-4, cardiac alpha-actin, and myosin heavy chain expression. These findings indicate the presence of a positive regulatory network between Nkx2-5 and MEF2C and show that both factors can direct early stages of cell differentiation into a cardiomyogenic pathway.

Refined localisation of the genes for nebulin and titin on chromosome 2q allows the assignment of nebulin as a candidate gene for autosomal recessive nemaline myopathy

A locus for autosomal recessive nemaline myopathy (NEM2) has been assigned by linkage analysis to a 13-cM region between the markers D2S150 and D2S142 on 2q21.2-q22. The genes for the giant muscle proteins nebulin and titin have previously been assigned by FISH to 2q24.1-q24.2 and 2q31, respectively. By using radiation hybrid mapping, we have reassigned the nebulin gene close to the microsatellite marker D2S2236 on 2q22 and the titin gene to the vicinity of the markers D2S384 and D2S364 on 2q24.3. The genomic orientation of the nebulin gene was determined as 5'-3' and of TTN as 3'-5' from the centromere. We conclude that the nebulin gene resides within the candidate region for NEM2 on the long arm of chromosome 2, while the titin gene is located outside this region.

Mutation segregation and rapid carrier detection of X-linked muscular dystrophy in dogs

OBJECTIVES

To use exon 7-specific genomic polymerase chain reaction (PCR) products to identify the genotypes of normal, affected, and carrier female dogs in pedigrees segregating Golden Retriever muscular dystrophy (GRMD), and to confirm the concordant segregation of the mutation in all carrier and affected dogs presently available.

DESIGN

The GRMD mutation is found in the consensus splice acceptor site in intron 6 of the canine dystrophin gene. PCR cycle-sequencing and restriction fragment length polymorphism/PCR were used for determination of the pattern of segregation of the point mutation which causes GRMD.

ANIMALS

Normal, clinically affected, and obligate carrier dogs in pedigrees of GRMD.

PROCEDURE

DNA from blood was amplified, using PCR and primers that bracket all of exon 7 of the canine dystrophin gene as well as 100 base pairs of intron on either side. PCR products were either cycle-sequenced directly or submitted to a second round of PCR, using 1 of the original primers coupled with a mutagenic restriction fragment length polymorphism-primer, which thus creates an artificial restriction site. Digestion with Stu I detected the normal allele. To detect the affected allele, Sau96 I was used to digest the 310-base pair exon 7 genomic fragment directly.

CONCLUSIONS

Simple, clear diagnosis of carrier status was possible using these methods. This mutation is passed through all carrier and affected dogs in both United States GRMD colonies and the colony in Australia.

CLINICAL RELEVANCE

Rapid, accurate diagnosis of carrier and affected dogs will enhance study of this homologue of Duchenne muscular dystrophy.

Organization of the vaccinia envelope and relationship to the structure of intracellular mature virions

Protrusions covering the surface of intracellular mature virions (IMV), termed by us surface tubular elements (STE), are released in a quasi-intact form during stripping of the envelope. The concentrated, reproducibly isolable STE were shown to contain the 58-kDa 4c polypeptide and prominent protein antigens residing at the surface of IMV. The major core protein 4b, identified as a minor contaminant of STE, presumably became detached along with STE during the shearing off process. Antibodies against protein 4b became specifically bound to the surface of isolated cores, where a palisade layer of rodlets occurs. The same antibodies absorbed onto isolated STE where similar rodlets were evident. Based on the new observations we constructed a model of the organization of the IMV envelope and its relationship to the core.

Detection and identification of multiple mycobacterial pathogens by DNA amplification in a single tube

A comparison of the DNA sequence of the 16S rRNA revealed a region in which there was a minor variation between the species of mycobacteria. This information was used to develop a multiplex amplification system that could identify the genus Mycobacterium and then distinguish between M. avium and M. intracellulare, two commonly encountered mycobacteria other than tuberculosis. The combination of these rRNA gene primers together with primers aimed at the MPB70 gene of M. tuberculosis complex organisms permits the detection and identification of clinically significant mycobacteria in a single tube. An amplification product of 1030 bp is indicative of the genus Mycobacterium and smaller fragments of 850, 372, and 180 bp are the positive signals for M. intracellulare, M. tuberculosis complex, and M. avium, respectively.

A prominent antigenic surface polypeptide involved in the biogenesis and function of the vaccinia virus envelope

Polypeptides of the vaccinia virus envelope exposed on the surface were identified by means of sulfo-N-hydroxysuccinimidobiotin as a surface tag. Among surface expressed polypeptides is the 35-kDa antigen, previously designated Ag35. Both monoclonal (mAb) and monospecific affinity pure antibodies directed against Ag35 neutralized vaccinia infectiousness, indicating that this prominent surface antigen has a function during early virus-host cell interactions. The binding of several monoclonal antibodies to various regions of Ag35 was tested by reacting CNBr fragments, derived from the polypeptide, employing Western blotting. All mAbs tested reacted with the same region of Ag35. Estimation of the molecular weights (MW), based on migration of the CNBr peptides in sodium dodecyl sulfate-polyacrylamide gel electrophoresis, revealed that those partial digestion products which contained a proline-rich 99 amino acid limit digest fragment were present at a position approximately 12.5 kDa larger than that predicted from the DNA sequence. By contrast, partial and limit digest products lacking the proline-rich fragment migrated to the MW position expected from the length of the DNA sequence. This observation demonstrates that departure from a predicted 22.3 kDa to an anomalous MW of Ag35 is conferred by the proline-rich peptide. The surface location of Ag35 was confirmed by immune electron microscopy. In a competition test the binding specificity of mAb and affinity-purified antibodies at the surface of virions could be demonstrated. Evidence for an association of Ag35 with the virus envelope at various stages during biogenesis of vaccinia was obtained by immune electron microscopy of whole mounts and thin sections. Presence of Ag35 as an early component of immature and mature virions, probably residing in the bilayer membrane structure was detected. A distinction can, therefore, be made between Ag35 and several other vaccinia envelope polypeptides which are synthesized as late functions and added during late stages of envelope assembly.

Relationship between RNA polymerase II and efficiency of vaccinia virus replication

It is clear from previous studies that host transcriptase or RNA polymerase II (pol II) has a role in poxvirus replication. To elucidate the participation of this enzyme further, in this study we examined several parameters related to pol II during the cycle of vaccinia virus infection in L-strain fibroblasts, HeLa cells, and L6H9 rat myoblasts. Nucleocytoplasmic transposition of pol II into virus factories and virions was assessed by immunofluorescence and immunoblotting by using anti-pol II immunoglobulin G. RNA polymerase activities were compared in nuclear extracts containing crude enzyme preparations. Rates of translation into cellular or viral polypeptides were ascertained by labeling with [35S]methionine. In L and HeLa cells, which produced vaccinia virus more abundantly, the rates of RNA polymerase and translation in controls and following infection were higher than in myoblasts. The data on synthesis and virus formation could be correlated with observations on transmigration of pol II, which was more efficient and complete in L and HeLa cells. The stimulus for pol II to leave the nucleus required the expression of both early and late viral functions. On the basis of current and past information, we suggest that mobilization of pol II depends on the efficiency of vaccina virus replication and furthermore that control over vaccinia virus production by the host is related to the content or availability (or both) of pol II in different cell types.

Phorbol ester-induced differentiation permits productive human cytomegalovirus infection in a monocytic cell line

The susceptibility of four different human cell lines (HUT 102, THP-1, MOLT-4, and HL-60) to infection by human CMV (HCMV) was studied. Only HUT 102 was susceptible and only immediate-early gene products were produced. However, THP-1, a monocytic cell line, could be infected by HCMV with a full cycle of replication after treatment with 12-O-tetradecanoyl-phorbol-13-acetate (TPA), which produced differentiation of the cell line into cells with characteristics of mature macrophages. Late (structural) Ag were demonstrated, as were infectious virions as detected by electron microscopy and infectious center assay. HL-60, a promyelocytic cell line, was not susceptible to HCMV infection after treatment with TPA despite differentiation into adherent cells with properties of macrophages, suggesting that cellular lineage was important. Treatment with TPA after infection resulted in a greatly reduced frequency of infected cells, suggesting that pretreatment was essential. Furthermore, continued presence of TPA was unnecessary after differentiation was induced. This study establishes the precedent of productive HCMV infection in human monocytic cells. The potential mechanism and relevance of enhanced replication induced by TPA are discussed.

Phorbol ester-induced differentiation permits productive human cytomegalovirus infection in a monocytic cell line

The susceptibility of four different human cell lines (HUT 102, THP-1, MOLT-4, and HL-60) to infection by human CMV (HCMV) was studied. Only HUT 102 was susceptible and only immediate-early gene products were produced. However, THP-1, a monocytic cell line, could be infected by HCMV with a full cycle of replication after treatment with 12-O-tetradecanoyl-phorbol-13-acetate (TPA), which produced differentiation of the cell line into cells with characteristics of mature macrophages. Late (structural) Ag were demonstrated, as were infectious virions as detected by electron microscopy and infectious center assay. HL-60, a promyelocytic cell line, was not susceptible to HCMV infection after treatment with TPA despite differentiation into adherent cells with properties of macrophages, suggesting that cellular lineage was important. Treatment with TPA after infection resulted in a greatly reduced frequency of infected cells, suggesting that pretreatment was essential. Furthermore, continued presence of TPA was unnecessary after differentiation was induced. This study establishes the precedent of productive HCMV infection in human monocytic cells. The potential mechanism and relevance of enhanced replication induced by TPA are discussed.

Influence of RNA polymerase II upon vaccinia virus-related translation examined by means of alpha-amanitin

Our previous studies employing alpha-amanitin-sensitive H-9 and resistant Ama 102 mutant host cells demonstrated that polymerase II (Pol II), or a drug-sensitive component of the enzyme, is required for replication of vaccinia virus. Evidence was also obtained indicating that transcription from the host genome does not appear to be involved (Silver et al., 1979; Silver and Dales, 1982), suggesting a possible role for Pol II in transcription from the viral genome. This idea is consistent with the present findings, based on immunofluorescence analysis, which revealed that upon infection Pol II antigen is mobilized out of the nucleus into discrete cytoplasmic foci. Effects of treating H-9 rat myoblasts with alpha-amanitin upon vaccinia-specific protein synthesis were also examined. Under the experimental conditions employed, the toxin drastically curtailed in vivo translation into early, late and late-late proteins without altering the spectrum of polypeptides produced. By contrast, treatment with the drug affected, only minimally, the rate of transcription into viral RNA, whether in vivo or from isolated vaccinia factories. The mRNA isolated from infected and treated or untreated cells was translated in a reticulocyte lysate with equal efficiency and general fidelity. This finding suggests that Pol II may be involved in transcription into RNAs related to factors controlling the in vivo translation process. The possible mechanisms for exercising such controls are discussed in relation to factors regulating transcription by host RNA polymerases from a viral DNA genome.

Identification of antigenic determinants by polyclonal and hybridoma antibodies induced during the course of infection by vaccinia virus

In order to extend the understanding of determinants involved in the humoral response in the infected host, mice were subjected to an immunization regimen using both active and uv-killed vaccinia virus. The spectrum of antibody specificity in hyperimmune sera was followed by Western blotting. Comparable studies involving Western blotting and immunofluorescence were conducted with a panel of monoclonal antibodies derived from hybridomas selected from similarly immunized animals. Hyperimmune sera contained circulating antibodies primarily against three polypeptides of 28K, 35K, and 62K. These antigens were shown to be located both at the surface and within the virion. The repertoire of monoclonal antibodies included some that reacted with the 28K and 35K antigens and others that recognized a 32K core complex component or a nonvirion cell surface component, corresponding to the viral hemagglutinin. Within the panel of monoclonal antibodies was a large group which reacted with a 32K antigen found in the IHD-J virion but absent from the IHD-W strain. This finding correlates with the absence of a 32K polypeptide from the IHD-W particle. Overall, the current findings reveal the absence of any particular correlation between the incidence of polyclonal antibodies in the circulation of the immune host and the frequency of selected hybridomas against vaccinia antigens. Application of this type of immunological analysis should provide useful data concerning the detection and mapping of the antigens and their epitopes which are significant for humoral immunity.

Biogenesis of poxviruses: role for the DNA-dependent RNA polymerase II of the host during expression of late functions

The participation of host RNA polymerase II in the vaccinia life cycle was examined by comparing efficiency of multiplication after treating the Ama+ sensitive and Ama 102 drug resistant lines with alpha-amanitin. In the latter, resistance is due to a mutation in RNA polymerase II. The toxin profoundly reduces synthesis of virus-specified polypeptides and morphopoeisis in Ama+ but not in Ama 102 rat myoblasts without appreciably altering vaccinia DNA replication in either cell type. This implicates RNA polymerase II in the expression of late virus functions. Circumstantial evidence from a model system indicates that gamma irradiation of the host prior to infection might disrupt transcription into functional mRNA from the nucleus. Irradiation does not, however, alter the capability of the host to support vaccinia multiplication fully. Therefore, ongoing host nuclear transcription may not be required by this virus. The above results are consistent with the ability of cytoplasts to produce small quantities of mature progeny. Our studies lead us to hypothesize that RNA polymerase II or a subunit of the host enzyme may participate directly in late transcription of the vaccinia genome.