Structural Basis of Egg Coat-Sperm Recognition at Fertilization.

Recognition between sperm and the egg surface marks the beginning of life in all sexually reproducing organisms. This fundamental biological event depends on the species-specific interaction between rapidly evolving counterpart molecules on the gametes. We report biochemical, crystallographic, and mutational studies of domain repeats 1-3 of invertebrate egg coat protein VERL and their interaction with cognate sperm protein lysin. VERL repeats fold like the functionally essential N-terminal repeat of mammalian sperm receptor ZP2, whose structure is also described here. Whereas sequence-divergent repeat 1 does not bind lysin, repeat 3 binds it non-species specifically via a high-affinity, largely hydrophobic interface. Due to its intermediate binding affinity, repeat 2 selectively interacts with lysin from the same species. Exposure of a highly positively charged surface of VERL-bound lysin suggests that complex formation both disrupts the organization of egg coat filaments and triggers their electrostatic repulsion, thereby opening a hole for sperm penetration and fusion.

The impact of essential oils on the qualitative properties, release profile, and stimuli-responsiveness of active food packaging nanocomposites.

Food industries attempt to introduce a new food packaging by blending essential oils (EOs) into the polymeric matrix as an active packaging, which has great ability to preserve the quality of food and increase its shelf life by releasing active compounds within storage. The main point in designing the active packaging is controlled-release of active substances for their enhanced activity. Biopolymers are functional substances, which suggest structural integrity to sense external stimuli like temperature, pH, or ionic strength. The controlled release of EOs from active packaging and their stimuli-responsive properties can be very important for practical applications of these novel biocomposites. EOs can affect the uniformity of the polymeric matrix and physical and structural characteristics of the composites, such as moisture content, solubility in water, water vapor transmission rate, elongation at break, and tensile strength. To measure the ingredients of EOs and their migration from food packaging, chromatographic methods can be used. A head-space-solid phase micro-extraction coupled to gas chromatography (HS-SPME-GC-MS) technique is as a good process for evaluating the release of Eos. Therefore, the aims of this review were to evaluate the qualitative characteristics, release profile, and stimuli-responsiveness of active and smart food packaging nanocomposites loaded with essential oils and developing such multi-faceted packaging for advanced applications.

COVID-19 vaccines: What dermatologists should know?

As COVID-19 vaccination has started worldwide to control this pandemic, dermatologists may face various challenges with these new vaccines. In this manuscript, we review different types of available COVID-19 vaccines and their various production platforms. Vaccination considerations in patients with skin diseases, especially those using immunomodulatory drugs will be presented. Finally, adverse cutaneous reactions of COVID-19 vaccines will be reviewed.

Systematic review and meta-analysis of safety and efficacy of high-intensity focused ultrasound (HIFU) for face and neck rejuvenation.

High-intensity focused ultrasound (HIFU) is widely used for skin rejuvenation and tightening. The aim of this study was to determine the safety and efficacy of HIFU for face and neck rejuvenation. A systematic search of peer reviewed articles published before December 2017 was performed using Medline, Web of Science, and Scopus databases. Retrieved studies were screened, and clinical trials or follow-up studies which were evaluated the effect of HIFU on rejuvenation treatments of face and neck area were included. Risk of bias for each study was assessed and was reported. Safety and efficacy variables, which were reported more often in papers, were included in meta-analysis. Seventeen studies involving 477 participants were included in the analysis. Meta-analysis showed moderate improvement as scores of 2.74 (95% CI 2.06-3.43) and 2.68 (95% CI 1.92-3.45), out of 5 maximum score, for objective improvement score and subjective satisfaction score, respectively. Meta-analysis of mean pain score, assessed by a 0-10 Likert score, was 4.2 (95% CI 4.27-5.19). Edema and erythema showed considerable heterogeneity, and no hyperpigmentation was reported by included studies. Included studies used multiple and different outcome variables with different scoring at various time points. Long follow-up was not reported by majority of studies. HIFU is safe procedure in short term and has a moderate effect on rejuvenation of face and neck areas.

Estimation of oxidative indices in the raw and roasted hazelnuts by accelerated shelf-life testing.

To estimate the oxidative stability of the raw and roasted hazelnuts, accelerated shelf-life testing (ASLT) was used at elevated temperatures (55, 65 and 75 °C) at water activity (aw) of 0.43. Chemical parameters, including peroxide value (PV), para-anisidine value, and total oxidation value were measured to estimate the oxidative stability of the samples using Arrhenius model. In addition, the samples were maintained for 8 months in a real condition at 20-30 °C (long-term shelf-life testing) for validating the results obtained from short-term ASLT. The maximum activation energy (Ea, 78.76 kJ/mol °K) and Q10 (1.871) was obtained for PV in raw hazelnuts, while the minimum Ea (53.36 kJ/mol °K) and Q10 (1.552) were recorded for PV in roasted hazelnuts, indicating the negative effect of roasting process on the oxidative stability of the samples. In order to validate the estimations, the values predicted by short-term ASLT for each oxidation index were plotted versus their corresponding values in actual storage. The results showed good correlation coefficients (R2 = 0.91-0.98), confirming the fitness of the Arrhenius model to predict the oxidative indices of the samples during normal storage.

Encapsulation of EPA and DHA concentrate from Kilka fish oil by milk proteins and evaluation of its oxidative stability.

Glyceride product from lipase-catalyzed hydrolysis of fish oil (large-scale) is a rich source of n-3 PUFA (49.62%); but it is prone to oxidation. Our aim was to encapsulate this product by a mixture of whey powder and sodium caseinate (4:1) as a new wall material. The emulsification was done using ultrasonication in different powers (180-380 W) and times (1-3 min) and, then, the emulsions were freeze-dried to obtain the powders. Based on encapsulation efficiency, sonication (88-94%) could inhibit the presence of oil at the surface of powder particles in comparison with the samples prepared without sonication (control, 68%). The highest oxidation rate and the lowest L-value were found for the unencapsulated glyceride product stored in air atmosphere followed by the control powder, the powders from sonication treatment and the unencapsulated glyceride product under N2, respectively. In the case of oxidative stability of the samples, the sonication time was more significant than sonication power. According to our results, a sonication treatment of 380 W for 3 min was recommended to prepare parent emulsions during fish oil encapsulation.

Can we improve the quality of medical news merely by increasing journalists' health knowledge?

Background: The aim of this study was to determine the effectiveness of an educational intervention on the quality of health research-based news, given the sensitivity of disseminating incorrect information. Methods: An uncontrolled before-after study was conducted among health news producers in Tehran from November 2011 to March 2012. The intervention that included educational content in the form of a workshop was evaluated in advance. The outcome of measuring the scientific quality of news extracted from medical and health research results was considered for authenticity and accuracy. The health research-based news quality assessment tool was used. In this study, 32 individuals voluntarily entered the program, and their produced news was collected in 4 stages. To determine the effectiveness of the educational intervention, paired t-tests were used. SPSS version 17 was used for statistical analysis and p<0.05 was considered significant. Results: The mean score (±SD) of the participants' produced news was 0.40 (±0.089) before and 0.61 (±0.086) after the intervention, which increased by 0.21±0.09 (p<0.001). Of the news collected from the participants as baseline data, 544 (65%) articles aimed at increasing public knowledge and awareness. Almost all the news had been gathered from interviews, and only 41 (4.8%) news articles were based on health research results. Conclusion: The educational intervention proved effective in promoting the quality of health research news. Only a few health journalists participated in this study, and thus the need to educate health news producers is felt. Since interviews with health researchers and experts were the largest source of news, interventions need to target other groups who affect the quality and accuracy of the news.

Comparison of clinical efficacy and safety of thermotherapy versus cryotherapy in treatment of skin warts: A randomized controlled trial.

The effect of thermotherapy in the treatment of skin warts in comparison to cryotherapy, as the standard conventional method, has remained uncertain. This study aimed to assess the clinical efficacy and safety of thermotherapy and cryotherapy in removing skin warts. This randomized controlled trial was conducted on 52 patients aged 18 years and over with ≤ 10 skin warts. The participants were randomly assigned into two groups to receive cryotherapy (every 2 to 3 weeks up to six sessions if required) or thermotherapy (one session). The patients in both groups were followed every 2 to 3 weeks for the first three months, and then three months after the last treatment session. The clearance rate was 79.2% in the thermotherapy group and 58.3% in the cryotherapy group with no significant difference (p = 0.212). The rate of scarring in the thermotherapy group was 20% (p = .018). A higher clearance rate was achieved in the thermotherapy group. However, this result was not statistically significant. There were some minimal post-treatment complications. Patients needed only one session of thermotherapy. Due to the risk of scarring, we suggest thermotherapy only as a suitable treatment method for palmoplantar warts.

Easy mammalian expression and crystallography of maltose-binding protein-fused human proteins.

We present a strategy to obtain milligrams of highly post-translationally modified eukaryotic proteins, transiently expressed in mammalian cells as rigid or cleavable fusions with a mammalianized version of bacterial maltose-binding protein (mMBP). This variant was engineered to combine mutations that enhance MBP solubility and affinity purification, as well as provide crystal-packing interactions for increased crystallizability. Using this cell type-independent approach, we could increase the expression of secreted and intracellular human proteins up to 200-fold. By molecular replacement with MBP, we readily determined five novel high-resolution structures of rigid fusions of targets that otherwise defied crystallization.

Pulmonary rehabilitation in Iranian outpatients with mustard gas lung disease: a randomised controlled trial.

OBJECTIVE: People with mustard gas lung disease experience cough, sputum, breathlessness and exercise limitation. We hypothesised that pulmonary rehabilitation (PR) would be beneficial in this condition. DESIGN: An assessor-blind, two-armed, parallel-design randomised controlled clinical trial. SETTING: Secondary care clinics in Iran. PARTICIPANTS: 60 men with breathlessness due to respiratory disease caused by documented mustard gas exposure, mean (SD) age 52.7 (4.36) years, MRC dyspnoea score 3.5 (0.7), St. George's Respiratory Questionnaire (SGRQ) 72.3 (15.2). INTERVENTIONS: Participants were allocated either to a 6-week course of thrice-weekly PR (n=31) or to usual care (n=29), with 6-week data for 28 and 26, respectively. OUTCOME MEASURES: Primary endpoint was change in cycle endurance time at 70% baseline exercise capacity at 6 weeks. Secondary endpoints included 6 min walk distance, quadriceps strength and bulk, body composition and health status. For logistical reasons, blood tests that had been originally planned were not performed and 12-month follow-up was available for only a small proportion. RESULTS: At 6 weeks, cycle endurance time increased from 377 (140) s to 787 (343) s with PR vs 495 (171) s to 479 (159) s for usual care, effect size +383 (231) s (p<0.001). PR also improved 6 min walk distance+103.2 m (63.6-142.9) (p<0.001), MRC dyspnoea score -0.36 (-0.65 to -0.07) (p=0.016) and quality of life; SGRQ -8.43 (-13.38 to -3.48) p<0.001, as well as quadriceps strength+9.28 Nm (1.89 to 16.66) p=0.015. CONCLUSION: These data suggest that PR can improve exercise capacity and quality of life in people with breathlessness due to mustard gas lung disease and support the wider provision of this form of care. TRIAL REGISTRATION NUMBER: IRCT2016051127848N1.

Immunogenicity and safety evaluation of a newly manufactured recombinant Baculovirus-Expressed quadrivalent influenza vaccine in adults 18 years old and Above: An Open-Label, phase III extension study.

In the face of global health threats, there is a growing demand for vaccines that can be manufactured on a large scale within compressed timeline. This study responds to this imperative by delving into the evaluation of FluGuard, a novel recombinant influenza vaccine developed by Nivad Pharmed Salamat Company in Iran. Positioned as a phase 3 extension, the research aimed to evaluate the safety and immunogenicity of FluGuard in volunteers aged 18 and above. The study was conducted as a single-center, open-label clinical trial. All eligible volunteers received FluGuard (2021-2022 Formula) on day 0. Safety assessments occurred at days 1, 4, 7, 14, 28 and 42 post-vaccination. Immunogenicity was measured through seroconversion, seroprotection, and geometric mean titer fold increase in subgroups of 250 volunteers. Among the 4,260 volunteers were screened and assessed for eligibility, 1000 were enrolled. At day 28 post-vaccination, seroconversion rates for A/H1N1, A/H3N2, B/Yamagata, B/Victoria were 53.4 % [95 %CI: 46.7-60], 57.7 % [95 %CI: 51.1-64.3], 54.3 % [95 %CI: 47.7-60.9], and 36.2 % [95 %CI: 29.8-42.6], respectively in volunteers 18 years and above. The most common solicited adverse events were pain at the injection site, malaise, and headache. No suspected unexpected adverse events and adverse events of special interest occurred during the study period. Our findings suggested that FluGuard® exhibits a desirable safety profile and provides sufficient immunogenicity against influenza virus types A and B. However, extended studies are warranted to assess the long-term protective efficacy. Trial Registration: The study protocol was accepted by Iranian registry of clinical trial; https://www.irct.ir; IRCT20201104049265N2.

Safety and immunogenicity of COReNAPCIN, a SARS-CoV-2 mRNA vaccine, as a fourth heterologous booster in healthy Iranian adults: A double-blind, randomized, placebo-controlled, phase 1 clinical trial with a six-month follow-up.

The recurrent COVID-19 infection, despite global vaccination, highlights the need for booster doses. A heterologous booster has been suggested to enhance immunity and protection against emerging variants of concern of the SARS-CoV-2 virus. In this report, we aimed to assess the safety, and immunogenicity of COReNAPCIN, as a fourth booster dose after three doses of inactivated vaccines. METHODS: The study was conducted as a double-blind, randomized, placebo-controlled phase 1 clinical trial of the mRNA-based vaccine candidate, COReNAPCIN. The vaccine was injected as a heterologous booster in healthy Iranian adults aged 18-50 who had previously received three doses of inactivated SARS-CoV-2 vaccines. In the study, 30 participants were randomly assigned to receive either COReNAPCIN in two different doses (25 µg and 50 µg) or placebo. The vaccine candidate contained mRNA encoding the complete sequence of the pre-fusion stabilized Spike protein of SARS-CoV-2, formulated within lipid nanoparticles. The primary endpoint was safety and the secondary objective was humoral immunogenicity until 6 months post-vaccination. The cellular immunogenicity was pursued as an exploratory outcome. RESULTS: COReNAPCIN was well tolerated in vaccinated individuals in both doses with no life-threatening or other serious adverse events. The most noticeable solicited adverse events were pain at the site of injection, fatigue and myalgia. Regarding the immunogenicity, despite the seroprevalence of SARS-CoV-2 antibodies due to the vaccination history for all and previous SARS-CoV-2 infection for some participants, the recipients of 25 and 50 µg COReNAPCIN, two weeks post-vaccination, showed 6·6 and 8·1 fold increase in the level of anti-RBD, and 11·5 and 21·7 fold increase in the level of anti-spike antibody, respectively. The geometric mean virus neutralizing titers reached 10.2 fold in the 25 µg group and 8.4 fold in 50 µg group of pre-boost levels. After 6 months, the measured anti-spike antibody concentration still maintains a geometric mean fold rise of 2.8 and 6.3, comparing the baseline levels in 25 and 50 µg groups, respectively. Additionally, the significant increase in the spike-specific IFN-ϒ T-cell response upon vaccination underscores the activation of cellular immunity. CONCLUSION: COReNAPCIN booster showed favorable safety, tolerability, and immunogenicity profile, supporting its further clinical development (Trial registration: IRCT20230131057293N1).

Reflective teaching and academic optimism as correlates of work engagement among university instructors.

As teaching is a complex and demanding activity especially in university and higher education contexts, exploring the correlates of work engagement in university contexts seems to be a promising research area. As an attempt to further clarify this research area, this study sought to examine the significance of reflective teaching and academic optimism as correlates of work engagement among university instructors in Iran. Having been selected via convenience sampling, a sample of 289 Iranian English as a foreign language (EFL) university instructors participated in this survey. The electronic versions of the scales of teacher academic optimism, reflective teaching, and work engagement were administered to the participants. Initially, the construct validity of the scales was verified for the university contexts via performing confirmatory factor analysis. Then the hypothesized structural relationships among the constructs were tested using structural equation modelling (SEM). The results demonstrated that both reflective teaching and academic optimism significantly predicted work engagement among English university instructors. Some notable implications are finally discussed based on these findings.

The influence of different gums compared with surfactants as encapsulating stabilizers on the thermal, storage, and low-pH stability of chlorophyllin.

Sodium copper chlorophyllin (SCC), with a higher stability and water solubility than chlorophyll, has limited applications in acidic products due to precipitation. We investigated the effect of pectin (PE), carboxymethyl cellulose (CMC), xanthan gum (XG), carrageenan gum (CG), gellan gum (GG), tragacanth gum (TG), gum Arabic (GA), and polysorbate 80 (PS80) on SCC stability in acidic model solutions (pH = 3.5). These stabilizers led to a significant reduction in particle size and zeta-potential compared to control sample. GA (33.3:1), PE (8:1), CMC (4:1), XG (1.33:1), and PS80 (0.67:1) stabilized SCC in acidic systems for 28 days. The FTIR analysis showed that mainly electrostatic and hydrogen bonds between SCC and stabilizers led to a substantial decline in particle size, improving SCC distribution and stability within acidic environment. Thus, XG and CMC could be effectively used for SCC stabilization under acidic solutions where applying PS80 surfactant is a health concern.

Efficacy and safety of "Jollab Monzej" as a traditional persian compound medicine for the treatment of multiple sclerosis-related fatigue: A randomized placebo-controlled trial.

Background: The purpose of this study was to investigate the efficacy and safety of Jollab monzej (JMZ), a Traditional Persian compound medicine, on multiple sclerosis-related fatigue (MSRF). Methods: We did a double-blind randomized controlled phase3 clinical trial on the JMZ syrup in fifty-six relapsing-remitting MS (RRMS) patients aged 18-55 years with moderate to severe fatigue using the Expanded Disability Status Scale (EDSS) score ≤ 6. We randomly assigned (1;1) participants to the JMZ syrup or placebo syrup groups treated for one month. Participants, investigators, and assessors were unaware of the assignments. The primary outcome was changes in the fatigue score on the Fatigue Severity Scale (FSS), at baseline and one month after treatment using the intention-to-treat (ITT) analysis. The secondary outcomes were changes in the score of Visual Analogue Scale (VAS), Beck Depression Inventory (BDI), and Pittsburgh Sleep Quality Index (PSQI). Outcomes were measured at baseline, one month after treatment, and 2-week follow-up. Safety was detected in all participants. Results: We randomly assigned 56 participants to the JMZ group (n=28) and placebo group (n=28). Fatigue scores significantly changed in both groups; however, the JMZ group had a greater reduction in FSS score in the ITT analysis. The adjusted mean difference was 8.80 (Confidence interval (CI) 95%, 2.90-14.70, P = 0.00). The mean difference of VAS, BDI, and global PSQI scores were statistically significant (P=0.01, P₌0.00, P₌0.01; respectively). Regarding safety, mild adverse events (AEs) were reported. Conclusion: The results of our study revealed that the administration of JMZ syrup alleviated MSRF and also could improve depression and sleep disorders.

Patient and Physician Perspectives in the Management of Immune Thrombocytopenia in Iran: Responses from the ITP World Impact Survey (I-WISh).

Data describing physicians' and patients' perspectives towards immune thrombocytopenia (ITP) management and impact of disease in Iran are limited. This ITP World Impact Survey was conducted between October 2019 and October 2020. Of the 114 patients included in the survey, 17 were aged ≤18 years. Forty-seven physicians, including 22 pediatric hematologists, participated in the survey. Fatigue and anxiety around stable platelet counts were frequent patient-reported symptoms at diagnosis and at survey completion. According to physicians, "watch-and-wait" was the preferred treatment option for mean (standard deviation) proportion of 50.1 (24.1) and 48.6 (21.8) of their adult and pediatric patients, respectively, following first diagnosis. Per adult and pediatric hematologists, the most prescribed treatments for newly diagnosed patients based on available answers were steroids (100%, n = 20/20; 89%, n = 16/18), respectively. Forty percent of adult (n = 10/25) and 38% of pediatric hematologists (n = 8/21) reported that ITP reduced patients' quality of life. Energy levels (46%, n = 52/112) and ability to concentrate on everyday activities (42%, n = 47/113) were the most affected aspects of patients' lives. This I-WISh study in Iran underlined the negative impact of ITP on patients.

The protection quest is a primary key to sharing the neutralizing antibody response to cover against all emerging VOCs based on BIV1-CovIran studies.

Over time, the antigenic evolution of emerging variants of SARS-CoV-2 has demanded the development of potential protective vaccines. Administration of additional doses of current vaccines based on the WT spike protein may boost immunity, but their effectiveness has dwindled for patients with more recent variants. Here, we studied the neutralization activity of post-WT strain-based vaccination and a structural simulation in-silico based on the interactions of the RBD-hACE2 as the key to initiating infection among the VOCs of SARS-CoV-2. Our data display shows that WT sera showed a markedly greater reduction in Delta and Omicron, suggesting that the Wuhan-based vaccines may be more susceptible to breakthrough and new VOCs. According to the MD simulation, mutations of Omicron result in a significant change in the variant charge distribution throughout the binding interface that consequently alters the critical interface electrostatic potential in comparison to other variants. This observation provides new insights into immunization policy and next-generation vaccine development.

Efficacy and safety of an inactivated virus-particle vaccine for SARS-CoV-2, BIV1-CovIran: randomised, placebo controlled, double blind, multicentre, phase 3 clinical trial.

OBJECTIVE: To report the efficacy, safety, and exploratory immunogenicity findings of two 5 µg doses of the BIV1-CovIran vaccine. DESIGN: Randomised, placebo controlled, double blind, multicentre, phase 3 clinical trial. SETTING: In six cities of Iran, including Bushehr, Isfahan, Karaj, Mashhad, Shiraz, and Tehran. The first vaccine or placebo injection of the first participant was on 16 May 2021 in Tehran. The last vaccine or placebo injection of the last participant occurred on 15 July 2021 in Isfahan. PARTICIPANTS: 20 000 participants aged 18-75 years were randomly assigned to the intervention or placebo groups with a ratio of 2:1. INTERVENTION: 5 µg vaccine or placebo with the interval of 28 days. MAIN OUTCOME MEASURES: Vaccine efficacy for a 90 day follow-up period, safety and explanatory immunogenicity assessment, and variant detection during the trial. RESULTS: 20 000 participants were recruited and randomly assigned to receive BIV1-CovIran (n=13 335 (66.7%)) or placebo (n=6665 (33.3%)). Participants' mean age was 38.3 (standard deviation 11.2) years, and 6913 (34.6%) were female. Among vaccinated participants that had covid-19 reported during the follow-up (median 83 days), 758 (5.9%) had symptoms, 144 (1.1%) had severe infection, and seven (0.1%) were critical. Among participants who received placebo during the follow-up, 688 (10.7%) had symptoms, 221 (3.4%) had severe infection, and 19 (0.3%) were critical. Overall efficacy was 50.2% (95% confidence interval 44.7% to 55.0%) against symptomatic covid-19, 70.5% (63.7% to 76.1%) against severe disease, and 83.1% (61.2% to 93.5%) against critical cases. Two deaths were reported in the efficacy population in the placebo group, no deaths were from the intervention group. During follow-up, 41 922 adverse events were reported: 28 782 (68.7%) were adverse reactions, of which 19 363 (67.3%) were in the intervention group. Most adverse reactions were mild or moderate in severity (grade 1 or 2) and self-limiting. No serious adverse events were related to the injections. For variant investigation, of 119 participants positive for the SARS-CoV-2 variant, 106 (89.1%) were positive for the delta variant. CONCLUSIONS: A two dose regimen of the BIV1-CovIran vaccine conferred efficacy of 50.2% against symptomatic covid-19, 70.5% against severe disease, and 83.1% against critical disease. Vaccination was well tolerated, with no safety concerns raised. TRIAL REGISTRATION: Iranian Registry of Clinical Trials, IRCT20201202049567N3. FUNDING: Shifa-Pharmed Industrial Group.

The molecular basis of sex: linking yeast to human.

Species-specific recognition between egg and sperm, a crucial event that marks the beginning of fertilization in multicellular organisms, mirrors the binding between haploid cells of opposite mating type in unicellular eukaryotes such as yeast. However, as implied by the lack of sequence similarity between sperm-binding regions of invertebrate and vertebrate egg coat proteins, these interactions are thought to rely on completely different molecular entities. Here, we argue that these recognition systems are, in fact, related: despite being separated by 0.6-1 billion years of evolution, functionally essential domains of a mollusc sperm receptor and a yeast mating protein adopt the same 3D fold as egg zona pellucida proteins mediating the binding between gametes in humans.

A model of classroom social climate, foreign language enjoyment, and student engagement among English as a foreign language learners.

With the advent of positive psychology in second language (L2) learning, some researchers have undertaken empirical studies to explore emotional variables affecting L2 learning and how positive emotions can enhance the engagement of L2 learners. As an attempt to contribute to this research domain, this project sought to test a model of student engagement based on classroom social climate (CSC) and foreign language enjoyment (FLE) among English language learners in Iran. A sample of 386 intermediate English as a foreign language (EFL) learners took part in this survey by completing the online battery of questionnaires. Structural equation modeling (SEM) was employed for the analysis of the gathered data. The results showed that both CSC and FLE were significant predictors of student engagement, with FLE acting as a stronger predictor. Furthermore, CSC exerted a slight influence on FLE. The findings of the present study verify the contributions of positive psychology to L2 pedagogy, implying that pleasant perceptions of learning context and positive emotions can lead to further student engagement.