Decreased IFNγ production correlates with diminished production of cytokines by dendritic cells in patients infected with hepatitis C virus and receiving therapy

Toll-like receptor (TLR) expression and the signalling pathways that lead to the production of accessory cytokines by antigen-presenting cells (APCs) both have potential to limit T-cell responses to viral antigens. Here, expression of TLR and retinoic acid inducible gene I (RIG-I) and responses evoked through these proteins were evaluated in patients chronically infected with HCV, before and during pegylated interferon-α (IFNα) and ribavirin therapy. Expression of TLR2, 3, 4, 7, 9 and RIG-I on APCs and cytokine production by DCs were measured by flow cytometry. Production of IL-12 by myeloid dendritic cells (mDCs), IFNα by plasmacytoid cells (pDCs) and IFNγ by peripheral blood mononuclear cells was measured after stimulation with TLR ligands. IFNγ ELISpot responses to HCV and CMV antigens declined on therapy. TLR and RIG-I expression on mDCs, pDCs, B cells and monocytes was either similar or higher in patients than that in controls and generally increased during therapy. Therapy impaired IL-12 and IFNα production by DCs and reduced production of IFNγ by PBMCs after stimulation with ligands for TLR3, TLR7/8, TLR9 and RIG-I. This was independent of whether patients attained a sustained virological response. HCV disease and interferon-based therapy reduced IFN-γ responses to HCV antigens and TLR agonists. This was not accompanied by reduced expression of pertinent TLR but correlated with diminished production of co-stimulatory cytokines by DCs stimulated via TLR.

Could a loss of memory T cells limit responses to hepatitis C virus (HCV) antigens in blood leucocytes from patients chronically infected with HCV before and during pegylated interferon-alpha and ribavirin therapy?

The proportions and activation status of T cells may influence responses to hepatitis C virus (HCV) and treatment outcome in patients receiving pegylated interferon (IFN)-alpha/ribavirin therapy. We confirmed that IFN-gamma enzyme-linked immunospot (ELISPOT) responses to HCV are poor in HCV patients and showed that responses to HCV and cytomegalovirus (CMV) antigens decrease during therapy. This was most apparent in patients with sustained virological response (SVR). Baseline frequencies of CD4+ effector memory (TEM) T cells were lower in SVR than non-SVR. Proportions of CD4+ and CD8+ TEM and terminally differentiated effector memory (TEMRA) T cells declined on therapy in SVR, as did proportions of Fas+ CD8+ TEMRA T cells. Baseline frequencies of programmed death (PD)-1-expressing CD4+ TEM and TEMRA T-cells were higher in SVR. Therapy increased percentages of PD-1+ CD4+ central memory (TCM) T cells and PD-1+ CD8+ TEM and TEMRA T cells in SVR. We conclude that successful therapy depletes circulating antigen-specific CD4+ T cell responses. This paralleled decreases in proportions of effector memory T cells and higher percentages of CD4+ TCM T cells expressing PD-1.

Obstructive endo-bronchial pseudotumour due to herpes simplex type 2 infection in an HIV-infected man

We report a 31-year-old man with an obstructive bronchial lesion due to herpes simplex type 2 infection, who responded promptly to endoscopic resection and oral treatment with acyclovir. Exophytic lesions of the respiratory tract are rare, potentially life-threatening, but readily treated complication of herpes simplex virus infection in HIV-infected individuals.

Evaluation of a diphtheria-tetanus-acellular pertussis-inactivated poliovirus-Haemophilus influenzae type b vaccine given concurrently with meningococcal group C conjugate vaccine at 2, 3 and 4 months of age

BACKGROUND AND OBJECTIVE

In view of the possible introduction of diphtheria-tetanus-acellular pertussis-inactivated poliovirus-Haemophilus influenzae type b (DTaP-IPV-Hib, eg Pediacel) vaccine in the UK, a study of the immunogenicity of Pediacel when given with one of two different meningococcal group C conjugate (MCC) vaccines at 2, 3 and 4 months of age was conducted.

METHODS

Randomised controlled study in 241 infants.

RESULTS

Post vaccination, the proportion of infants with anti-polyribosylribitol phosphate (PRP) levels > or =0.15 microg/ml was 93.2% (95% confidence interval (CI) 86.6 to 96.7) in the Pediacel group compared with 100% (95% CI 96.4 to 100) in the diphtheria-tetanus-whole-cell pertussis-Haemophilus influenzae type b (DTwP-Hib) group. The anti-PRP response was lower in infants receiving either Pediacel or DTwP-Hib when these vaccines were given concomitantly with meningococcal group C conjugate with diphtheria-derived protein CRM(197) as conjugate protein (MCC-CRM) compared with meningococcal group C conjugate with tetanus toxoid as conjugate protein (MCC-TT). For group C meningococcus, the proportion of infants with serum bactericidal antibody (SBA) titre > or =1:8 in the Pediacel group was 99.0% compared with 100% in the DTwP-Hib group. The MCC SBA geometric mean titre (GMT) was lower in those receiving Pediacel with MCC-TT than in those receiving DTwP-Hib with MCC-TT, although all titres were well above the protective threshold. The MCC SBA GMT was similar in those receiving Pediacel and DTwP-Hib and MCC-CRM. Responses to all other vaccine components were equivalent in the two groups.

CONCLUSIONS

Pediacel is immunogenic when given at 2, 3 and 4 months of age. Coadministration of MCC vaccine can influence the Hib response, and the MCC response to a tetanus conjugate can be influenced by the nature of the coadministered DTP-Hib vaccine.

Universal hepatitis B vaccination of UK adolescents: a feasibility and acceptability study

The feasibility of introducing universal hepatitis B immunisation was assessed by offering the vaccine to all 11-12 year old pupils in Greater Glasgow (approximately 10,800). Consent was received from 92% of the school roll, and 91.3%, 89.2% and 80.3% received at least 1, at least 2, and 3 doses respectively. The findings of this study constitute key evidence for the ongoing debate in the UK on hepatitis B vaccination.

Efficacy of low-dose oral use of type I interferon in cytomegalovirus infections in vivo

Oral administration of type I interferons (IFNs; murine IFN-alpha and IFN-beta) reduces early replication of murine cytomegalovirus (MCMV) in both the spleen and liver of MCMV-infected BALB/c mice. Examination of a range of doses of IFN (1 to 1000 IU) showed that 10 IU administered daily for 1 week prior to virus infection was optimal for inhibition of MCMV replication. Furthermore, low-dose orally administered IFN (10 IU/day) was effective in mice challenged with lethal and sublethal virus inocula. The antiviral efficacy of low-dose orally administered IFN was not restricted by either the route of virus inoculation or the mouse genotype. Analysis by immunohistochemistry of IFN-alpha receptor-bearing cells of the gastrointestinal tract revealed predominant staining of perivascular smooth muscle and the lamina propria of the anterior tongue, small intestine and rectum. These tissues, dense in IFN-alpha receptor-bearing cells, are likely to be the sites of interaction of the orally administered IFNs with the mucosal immune system. In conclusion, we propose that low-dose oral use of type I IFN therapy may have broad applications in the treatment of CMV infections.

Bartonella henselae associated with Parinaud's oculoglandular syndrome

Bartonella henselae was recovered from the conjunctival scraping of a 38-year-old woman who presented with a 2-week history of tender preauricular lymphadenopathy and a 1-day history of a red left eye. Dry adherent colonies were observed on agar plates at 21 days of incubation, and the isolate was identified through conventional and molecular tests. Polymerase chain reaction (PCR) amplification of a specific region of the 16S rRNA gene and confirmation by a separate PCR reaction with hybridization of the product with a B. henselae-specific probe confirmed the isolate as B. henselae. This is the first reported isolation of the causative agent of cat scratch disease from ocular tissue in a patient with Parinaud's oculoglandular syndrome.

Low-dose oral type I interferons reduce early virus replication of murine cytomegalovirus in vivo

Immunity to viral infections involves both innate and antigen-specific immune responses. The antiviral properties of interferons (IFNs) are part of the innate immune response. Low doses of type I IFNs (IFN-alpha and IFN-beta) administered daily (10 IU per mouse) by the oral route significantly reduced the early replication of murine cytomegalovirus (MCMV) in both the spleen and liver of MCMV-infected susceptible BALB/c mice. Significant inhibition of virus replication was observed for two different inoculum doses of virus (2 x 10(4) pfu per mouse [0.6 LD50] and 2 x 10(4.12) pfu per mouse [0.8 LD50]). Analysis of IFN retention, using [35S]-labeled IFN-alpha1 compared with the nonreceptor binding mutant IFN-alpha1 (R33M) administered orally to mice, revealed binding of wild-type IFN-alpha1 to several tissues. In particular, IFN was retained by tissues proximal to lymphoid regions, including the posterior nasal cavity, posterior tongue, small intestine, and rectum. These findings suggest that type I IFNs may inhibit MCMV replication by distal binding of the orally administered IFN to various tissues, which in turn augment the primary immune response to virus infection.

The relationship of self-esteem to the health-related behaviors of the patients of a primary care clinic

To clarify the relationship of self-esteem and health-related behaviors of primary care clinic patients, 500 family practice residency patients were invited to complete self-esteem and health-risk appraisal instruments. Of the final subject pool (N = 469), 154 responded to the single-mailing solicitation, thereby yielding a 32.8% response rate. Correlational analysis found self-esteem to be associated with predicted longevity, life satisfaction, social ties, overall health, personal loss, seatbelt use, age, physical activity, smoking, exposure to violence, and substance use. Multiple regression analysis of male subjects' data found self-esteem most closely related to the frequency of exposure to danger, self-perceptions of health, and tobacco use. Similar analysis of the women's data most closely associated self-esteem to perceived social support, self-perception of health, diastolic blood pressure, and seatbelt use. The data clearly link individuals' self-esteem to predicted longevity. Those with greater self-regard were predicted to live longer, while those with poorer self-esteem achieved shorter predicted longevity. Contributing factors may have included greater emphasis on self-care.

Cloning of a unique sequence specific to isolates of type B:2 Pasteurella multocida

Two Carter type B Pasteurella multocida isolates, Izatnagar 52 and 25, isolated from cases of haemorrhagic septicaemia (HS), were used in a modified subtractive hybridisation technique with the specific aim of cloning unique DNA sequences related to the pathogenesis of HS. Biochemical and protein analyses have shown these isolates to be similar, but reports indicate that they have differences in pathogenicity. The subtracted inserts were screened against genomic DNA from a wide range of P multocida isolates, with two distinct fragments demonstrating specific hybridisation with Carter type B isolates that cause HS. No identity was observed with either Carter type E isolates or non-HS type B strains. The clones were sequenced and a search of the GenBank database revealed significant identity of the clone A3b (296 nt) to P haemolytica lipoprotein, whereas there was no significant identity with 6b (956 nt). Both these fragments had a high level of identity (72.8 to 76.9 per cent) to the H influenzae Rd genome.

Ascorbate attenuates the systemic kainate-induced neurotoxicity in the rat hippocampus

The neuronal damage induced by systemic administration of kainic acid reproduces the cellular and regional pattern of damage produced by repeated seizures. The ability of kainic acid to induce lipid peroxidation, and the ability of free radical inhibitors to prevent ischaemically-induced cell death, has led us to examine the possible role of free radicals in kainate-induced injury. Ascorbic acid was able to reduce kainate-induced damage of the rat hippocampus, measured by means of the gliotic marker ligand [3H]PK11195. Ascorbate was significantly effective at doses of 30 mg kg-1 and above, with total protection against kainate at 50 mg kg-1. Histologically, ascorbate at 50 mg kg-1 was able to prevent kainate-induced neuronal loss in the hippocampal CA1 and CA3a cell layers. The antioxidant was also effective when administered simultaneously with, or 1 h before the kainate. Protection was also obtained by allopurinol, 175 mg kg-1 and by oxypurinol, 40 mg kg-1. Ascorbate did not modify synaptically evoked potentials or long-term potentiation in hippocampal slices, ruling out any blocking activity at glutamate receptors. It is concluded that the neuronal damage produced by systemically administered kainate involves the formation of free radicals.

Serum rotavirus neutralizing-antibody titers compared by plaque reduction and enzyme-linked immunosorbent assay-based neutralization assays

Comparisons in rotavirus neutralizing-antibody responses were made with sera collected from vaccinated infants. The methods were a plaque reduction assay and a new enzyme-linked immunosorbent assay-based neutralization assay. Agreement of 94% was found in detecting at least fourfold seroresponses, and correlation coefficients between titers obtained by the two methods showed excellent agreement, indicating that either could be used reliably.

The CrP operon of Chlamydia psittaci and Chlamydia pneumoniae

One of the critical developmental events during the unique intracellular life cycle of Chlamydiae is their differentiation from a metabolically active, replicative form or reticulate body (RB) to an infectious extracellular form of the organism (elementary body or EB). This process is characterized by the expression of two extraordinarily cysteine-rich envelope proteins of molecular masses 9 kDa and 60 kDa. We describe the molecular cloning and sequence determination of the 9 kDa cysteine-rich proteins (CrPs) of C. pneumoniae and C. psittaci. Comparison of these 9 kDa CrP amino acid sequences with those of C. trachomatis showed regions of structural variation and conservation. Transcription of the 9 kDa CrP genes occurred as both a monocistronic message and as a bicistronic message which included the 60 kDa CrP gene. Transcription of the 9 kDa and 60 kDa CrP genes was tightly linked to the chlamydial growth cycle with synthesis of their mRNAs and consequent translation of the 60 kDa CrPs occurring as RBs differentiated to form EBs. The maximal rate of transcription occurred late in the growth cycle from a single but highly conserved promoter which had close similarity with the Escherichia coli consensus promoter sequences. A stem and loop structure which could be involved in regulating translation of mRNA occurred in all three species between the transcriptional start point and the ribosome binding site. Although transcription is initiated from a single promoter in all three chlamydial species, transcriptional termination points for the monocistronic and bicistronic mRNAs differ in both number and position.

Immunoreactivity of the 60 kDa cysteine-rich proteins of Chlamydia trachomatis, Chlamydia psittaci and Chlamydia pneumoniae expressed in Escherichia coli

The 60 kDa cysteine-rich proteins (CrPs) of Chlamydia are developmentally regulated outer envelope proteins synthesized late in the chlamydial growth cycle. These proteins, found only on the extracellular infectious elementary bodies, elicit major antibody responses in chlamydial infection. We have cloned and expressed in Escherichia coli the complete 60 kDa CrP genes from Chlamydia trachomatis, C. psittaci and C. pneumoniae. The recombinant products were expressed as either 'native' proteins or as fusions with the bacteriophage T7 gene 10 protein. Electron microscopy showed that recombinant proteins were produced as insoluble inclusions within the E. coli host cells. The recombinant 60 kDa CrPs were purified and used to raise high titre polyclonal antisera. In immunoblot analysis these antisera reacted with the 60 kDa CrPs from purified elementary bodies of all three chlamydial species in a genus-specific manner. Further molecular analysis allowed the genus-specific cross-reacting epitopes to be localized by using overlapping synthetic peptides covering the C. trachomatis 60 kDa CrP. Immunogold labelling experiments, using purified infectious elementary bodies from the three chlamydial species indicated that the 60 kDa CrPs are not surface accessible to antibody binding.

Are individual differences in fantasy play related to peer acceptance levels?

Individual differences in fantasy play, as they relate to cognitive competence and peer acceptance, were examined in a sample of 66 children between the ages of 4 and 8 years. Each child's free-play behaviors were videotaped and then coded for frequency of fantasy play and nonfantasy play, as well as for the unreality level and unfamiliarity level of the fantasy play. Solitary play was rarely observed; therefore all play measures that were coded were social (i.e., play involving at least one partner). Cognitive competence measures included self-ratings and teacher ratings of academic skills. Peer acceptance measures included self-ratings and teacher ratings of friendships and social activities. Results showed that high-fantasy players had higher self-ratings of peer acceptance than did average-fantasy players. High-fantasy players, however, had lower teacher ratings of peer acceptance than did average-fantasy players. These differential relations could be related to an inability on the part of high-fantasy players to distinguish imagined popularity from actual peer acceptance levels. Future research is recommended to provide more detailed characterizations of individual differences in fantasy play and how they relate to outcomes in the social, cognitive, and affective domains.

Preschool children's symbolic representation of objects through gestures

To investigate the symbolic quality of preschoolers' gestural representations in the absence of real objects, 48 children (16 3-, 4-, and 5-year-olds) performed 2 tasks. In the first task, they were asked to pretend to use 8 common objects (e.g., "pretend to brush your teeth with a toothbrush"). There was an age-related progression in the symbolic quality of gestural representations. 3- and 4-year-olds used mostly body part gestures (e.g., using an extended finger as the toothbrush), whereas 5-year-olds used imaginary object gestures (e.g., pretending to hold an imaginary toothbrush). To determine if children's symbolic skill is sufficiently flexible to allow them to use gestures other than those spontaneously produced in the first task, in the second task children were asked to imitate, for each object, a gesture modeled by an experimenter. The modeled gesture was different from the one the child performed on the first task (e.g., if the child used a body part gesture to represent a particular object, the experimenter modeled an imaginary object gesture for that object). Ability to imitate modeled gestures was positively related to age but was also influenced by the symbolic mode of gesture. 3-year-olds could not imitate imaginary object gestures as well as body part gestures, suggesting that young preschoolers have difficulty performing symbolic acts that exceed their symbolic level even when the acts are modeled. Results from both tasks provide strong evidence for a developmental progression from concrete body part to more abstract imaginary object gestural representations during the preschool years.

Genetic diversity and identification of human infection by amplification of the chlamydial 60-kilodalton cysteine-rich outer membrane protein gene

The 60-kDa cysteine-rich outer membrane protein genes of Chlamydia psittaci, Chlamydia pneumoniae, and Chlamydia trachomatis have very different 5' ends, but two areas flanking this variable region show absolute sequence conservation. This observation permitted differentiation of the three species of Chlamydia by the polymerase chain reaction (PCR), forming the basis of a diagnostic test for chlamydial infections. The PCR product containing the variable region of the respective 60-kDa CrP genes was also subjected to restriction endonuclease digestion, enabling differentiation of individual type strains of C. psittaci. Differentiation was possible between lymphogranuloma venereum and trachoma isolates of C. trachomatis. The PCR-based diagnostic test was successful with all strains of chlamydiae studied. The PCR primers showed high specificity and did not produce any product with common bacterial pathogens that may share the same sites of infection.

Metabolism of 99mTc-L,L-ethyl cysteinate dimer in healthy volunteers

99mTc-L,L-Ethyl cysteinate dimer (ECD) is a brain-perfusion imaging agent, which exhibits selective retention in brain and rapid renal excretion. The pharmacokinetics and metabolism of ECD were studied in vivo in healthy humans and its metabolism in vitro was evaluated in tissue from human brain. In vitro studies showed 99mTc-L,L-ECD to be metabolized to a polar 99mTc-complex. It has been shown previously that most of the activity of 99mTc retained in the brain of the monkey in vivo is in the form of a polar 99mTc complex (Walovitch, Hill, Garrity, Cheesman, Burgess, O'Leary, Watson, Ganey, Morgan and Williams, 1989). Whole body images of the distribution of 99mTc-L,L-ECD (10 mCi i.v.) in four adult males showed good uptake in brain, with slow elimination (6.8 +/- 0.3% injected dose [mean +/- SE] at 5 min), with less than 25% decrease in activity during 4 hr of imaging. Background areas in the head and lungs washed out rapidly, providing ideal imaging conditions. Elimination of 99mTc from venous blood was biphasic, with a plateau of activity between 2-15 min (7-8% injected dose) before a terminal phase, with a t1/2 of a few hours. Organic extraction of whole venous blood showed greater than 50% of the 99mTc-L,L-ECD to be in the form of polar metabolite(s) at 5 min. They were identified in the urine as the 99mTc ethylenediylbis-L-cysteine, monoethyl ester complex (ECM) and the 99mTc-ethylenediylbis-L-cysteine complex (EC). These metabolites were excreted rapidly (75% injected dose in urine within 6 hr). The results of this study support the hypothesis that the selective retention in brain, rapid blood elimination and renal excretion of 99mTc-L,L-ECD is due to its metabolic transformation to polar end products.

Chlamydia trachomatis 60 kDa cysteine rich outer membrane protein: sequence homology between trachoma and LGV biovars

An 820 bp AccI-PstI fragment of the 60 kDa cysteine rich outer membrane protein (CrP) gene from C. trachomatis serovar L1 was used as a probe to locate the 60 kDa CrP gene of a recent serovar B trachoma isolate (Jali 20/OT). The probe hybridized to a single 1.8 kb SpeI fragment in Southern blot analyses of different restriction endonuclease digests of C. trachomatis serovar B DNA. This fragment was ligated into Lambda Zap II arms and Bluescript SK(-) recombinants, released by infection with the helper phage R408, were used as template for DNA sequence determination. Sequence analysis demonstrated a very high level of homology between the Jali 20/OT 60 kDa CrP and the previously published serovar L1 60 kDa CrP with only 8 out of 507 amino acid substitutions between the two proteins.

Treatment of tardive dyskinesia: preliminary report on use of tetrabenazine

Tetrabenazine has been used for treatment of tardive dyskinesia sporadically over the past twenty years. Dose has usually been decided empirically without assaying blood levels. This report describes 23 cases treated successfully with tetrabenazine. Our method of measuring levels of tetrabenazine and its metabolites in biological samples is described briefly.

Pharmacokinetics of tetrabenazine and its major metabolite in man and rat. Bioavailability and dose dependency studies

The pharmacokinetics of tetrabenazine (TBZ), a catecholamine and serotonin depletor, and its major metabolite, dihydrotetrabenazine (HTBZ), were studied in four patients affected by tardive dyskinesia, who were under treatment with different doses of TBZ (12.5-37.5 mg, t.i.d.), and in the rat. In the patients, the steady-state area under the plasma concentration-time curves (AUCs) of the metabolite were 82.6-199-fold higher than those of TBZ. The drug showed a small and erratic bioavailability (F = 0.06 +/- 0.026, mean +/- SD). It appears to be extensively metabolized, as no unchanged TBZ could be detected in the urine of the patients. Single oral doses of 0.5-10 mg/kg and single iv dose of 1 mg/kg of TBZ were each administered to four to six rats. The clearance of the drug following iv administration to the rat (mean +/- SD, 58.9 +/- 6.01 ml X min-1 X kg-1) was very close to the rat hepatic blood flow indicating a perfusion-limited clearance. An F value of 0.17 was obtained following iv and po doses of 1 mg/kg TBZ in the rat. The oral absorption of TBZ seems to be rapid and almost complete. Plots of the AUCs of TBZ and HTBZ vs. five different po doses (0.5-10 mg/kg) were linear with correlation coefficients of 0.998 and 0.986 for TBZ and HTBZ, respectively, suggesting linear kinetics in the examined dosage range. In both the patients and rats, the plasma profile of TBZ followed characteristics of a multiexponential pharmacokinetic model.(ABSTRACT TRUNCATED AT 250 WORDS)

Direct injection high-performance liquid chromatography of tetrabenazine and its metabolite in plasma of humans and rats

A convenient, selective, and sensitive reversed-phase HPLC assay was developed to measure concentrations of the dopamine-depleting agent, tetrabenazine (1,3,4,6,7,11b-hexahydro-3-isobutyl-9,10-dimethoxy-2H-benzo(a)quinoli zin-2-one) and its dihydro metabolite in the plasma of patients with tardive dyskinesia receiving therapeutic doses of the drug and in the plasma of rats. The method involves plasma protein precipitation, oxidation of the compounds with mercuric acetate at 110 degrees C for 1 h, addition of internal standard, and injection into the instrument. Fluorescence detection was utilized at excitation and emission wavelengths of 265 and 418 nm, respectively. The peaks from the drug, its metabolite, and at least three other substances were best resolved at 60 degrees C using a mobile phase of water:acetonitrile:acetic acid:triethylamine (65:33:2:0.15) at a flow rate of 0.6 mL/min; the 4.6 mm X 10 cm column contained 5 micron of octadecylsilane packing. To assess the applicability of the assay, the drug was administered intravenously to rats, and plasma concentrations were determined before (by UV-HPLC) and after (by fluorescence-HPLC) the oxidative procedure. In addition, the MS spectra of tetrabenazine and the dihydro metabolite, isolated from biological samples, were identical to those of authentic samples. Excellent linearity was observed between the peak area ratios and concentrations over the ranges 0.5-200 and 2-1000 ng/mL of the drug and the metabolite, respectively. Minimum quantifiable concentrations of the drug and its metabolite were 0.5 and 2.0 ng/mL, respectively. The sensitivity was found to be adequate for pharmacokinetic studies of tetrabenazine in humans and rats.

Agents and recipient objects in the development of early symbolic play

The development of 2 components of early symbolic play--children's symbolic transformations of agents of action and recipient objects of action--was assessed in 48 children from 14 to 25 months of age. A 5-step sequence was predicted based on a combined weighting of agent substitutions and recipient object substitutions in each step. Children observed an adult model who pretended to talk into a telephone using each agent and object substitution in all combinations and then were allowed to demonstrate their own imitative pretending for each step. Based on the children's profiles of steps passed and failed, the sequence was found to form a Guttman scale and be age related. 2 types of possible underlying sequences were discussed.