Lupus IgA1 autoantibodies synergize with IgG to enhance plasmacytoid dendritic cell responses to RNA-containing immune complexes.

Autoantibodies to nuclear antigens are hallmarks of systemic lupus erythematosus (SLE) where they contribute to pathogenesis. However, there remains a gap in our knowledge regarding how different isotypes of autoantibodies contribute to this autoimmune disease, including the production of the critical type I interferon (IFN) cytokines by plasmacytoid dendritic cells (pDCs) in response to immune complexes (ICs). We focused on IgA, which is the second-most prevalent isotype in serum and, along with IgG, is deposited in glomeruli in individuals with lupus nephritis. We show that individuals with SLE have serum IgA autoantibodies against most nuclear antigens, correlating with IgG against the same antigen. We investigated whether IgA autoantibodies against a major SLE autoantigen, Smith ribonucleoprotein (Sm/RNP), played a role in IC activation of pDCs. We found that pDCs expressed the IgA-specific Fc receptor, FcαR, and IgA1 autoantibodies synergized with IgG in RNA-containing ICs to generate robust primary blood pDC IFN-α responses in vitro. pDC responses to these ICs required both FcαR and FcγRIIa, showing synergy between these Fc receptors. Sm/RNP IC binding to and internalization by pDCs were greater when ICs contained both IgA1 and IgG. Circulating pDCs from individuals with SLE had higher binding of IgA1-containing ICs and higher expression of FcαR than pDCs from healthy control individuals. Although pDC FcαR expression correlated with the blood IFN-stimulated gene signature in SLE, Toll-like receptor 7 agonists, but not IFN-α, up-regulated pDC FcαR expression in vitro. Together, we show a mechanism by which IgA1 autoantibodies contribute to SLE pathogenesis.

Antibrush Border Antibody Disease: A Case Series.

Antibrush border antibody (ABBA) disease is a rare cause of kidney disease characterized by progressive renal tubular injury associated with immune complex deposition along the basement membranes of the proximal tubule and circulating autoantibodies to brush border antigens. Several antigens have been identified as targets of autoantibodies in this disease, including low-density lipoprotein receptor related protein 2 (LRP2), cubilin, and amnionless proteins. We present 9 patients from 2 academic medical centers and describe the clinicopathologic characteristics and outcome data. All patients presented with acute kidney injury and proteinuria. Pathology confirmed immune complex deposition along proximal tubular basement membranes in all patients, but the majority (6/8) also showed segmental glomerular subepithelial immune complexes. Two of 3 patients treated with rituximab demonstrated stabilization of kidney function; 1 of these patients had mantle cell lymphoma. One patient with lung cancer showed stabilization of disease after treatment of the malignancy. The remaining patients progressed to end-stage kidney disease with either conservative therapy (3 patients) or immunosuppression with glucocorticoids (2 patients). This series highlights the poor prognosis of ABBA disease, but a potential benefit of anti-B cell therapy or treatment of an underlying malignancy in some cases.

Interferon-γ induces combined pyroptotic angiopathy and APOL1 expression in human kidney disease.

Elevated interferon (IFN) signaling is associated with kidney diseases including COVID-19, HIV, and apolipoprotein-L1 (APOL1) nephropathy, but whether IFNs directly contribute to nephrotoxicity remains unclear. Using human kidney organoids, primary endothelial cells, and patient samples, we demonstrate that IFN-γ induces pyroptotic angiopathy in combination with APOL1 expression. Single-cell RNA sequencing, immunoblotting, and quantitative fluorescence-based assays reveal that IFN-γ-mediated expression of APOL1 is accompanied by pyroptotic endothelial network degradation in organoids. Pharmacological blockade of IFN-γ signaling inhibits APOL1 expression, prevents upregulation of pyroptosis-associated genes, and rescues vascular networks. Multiomic analyses in patients with COVID-19, proteinuric kidney disease, and collapsing glomerulopathy similarly demonstrate increased IFN signaling and pyroptosis-associated gene expression correlating with accelerated renal disease progression. Our results reveal that IFN-γ signaling simultaneously induces endothelial injury and primes renal cells for pyroptosis, suggesting a combinatorial mechanism for APOL1-mediated collapsing glomerulopathy, which can be targeted therapeutically.

Commentary: Engagement for Research and Quality Improvement - More Than Just Words.

We reflect on the paper from Hahn-Goldberg et al. (2024) who shared key learnings from a pan-Canadian quality improvement (QI) and patient engagement care transition initiative called Bridge-to-Home. In considering the approach and outcomes presented in their paper, we have generated reflections and practical suggestions on how to amplify engagement work even further: (1) patient engagement and QI are about relationships; (2) seamlessly implementing complex interventions across siloed organizations continues to be a challenge, which engagement alone cannot solve; (3) it is time for a paradigm shift; (4) QI is about human behaviour change and is inherently messy; and (5) embedding fulsome evaluation of engagement is essential.

Establishment of a Biorepository for Down Syndrome: Experience of the Inter-Institutional Multidisciplinary BioBank - BioBIM.

BACKGROUND: Down syndrome, or Trisomy 21, is the leading genetic cause of cognitive disability in children and is associated with a high risk of several comorbidities, particularly congenital heart defects, early onset Alzheimer's disease, leukaemia, and autoimmune disorders. OBJECTIVE: This study describes the design, methods, and operational procedures employed to establish a biobank dedicated to Down syndrome that can support research projects investigating the effects of various genetic and environmental factors on this complex disease. METHODS: Blood was collected from all recruited subjects, processed, aliquoted and immediately frozen at -80 °C in the Interinstitutional Multidisciplinary BioBank (BioBIM) facilities. A small aliquot of the sample was used to perform blood tests for which analysis would not be feasible at a later date, such as blood cell counts. Each biological sample was coded, assigned a Standard PREanalytical Code, and registered in the oloBIOBANK software connected to a medical card containing all the donor's anamnestic data. All samples were stored under continuous real-time temperature recording using a freezer connected to a T-GUARD alarm system. In addition, a radiofrequency identification tracking system strictly monitored each cryopreservation operation performed throughout the sample lifecycle. RESULTS: Biological samples were collected from 454 individuals with Down syndrome from 2007 to 2023. A total of 2233 biological samples were available for research purposes, including whole blood in different anticoagulants, serum, plasma, and frozen peripheral blood mononuclear cells. The quality of the nucleic acids obtained through specific standard operating procedures demonstrated that these samples were appropriate for clinical and basic research. CONCLUSION: By establishing this biobank, we have gathered a significant number of biological samples and clinical data from individuals with Down syndrome, thereby fostering collaboration between different research groups in an open and transparent manner. Sharing expertise and resources among scientists will ultimately facilitate the transfer of knowledge to clinical practice, leading to the development of more effective therapeutic treatments to improve the outcomes and quality of life of patients with Down syndrome.

How do people with intellectual disabilities understand friendship? A systematic meta-synthesis.

BACKGROUND: Previous systematic reviews of the relationships of people with intellectual disabilities have included consideration of intimate relationships. In this paper, we report a systematic review of papers describing friendship only. METHOD: A systematic qualitative meta-synthesis of the research exploring experiences of friendship as reported by people with intellectual disabilities. RESULTS: Seven papers met the inclusion criteria for analysis. Three superordinate themes were identified. (1) Reciprocity, 'Someone who helps me, and I help them'. (2) The building blocks of friendships, 'I can tell her some secrets'. (3) Managing friendship difficulties, 'In real life it's much harder'. CONCLUSION: People with intellectual disabilities value friendship and actively engage in reciprocal exchanges. We explore the strengths and limitations of current research, clinical implications, and directions for future research.

Flagellin-modulated inflammasome pathways characterize the human alveolar macrophage response to Burkholderia pseudomallei, a lung-tropic pathogen.

Melioidosis is an emerging tropical infection caused by inhalation, inoculation, or ingestion of the flagellated, facultatively intracellular pathogen Burkholderia pseudomallei. The melioidosis case fatality rate is often high, and pneumonia, the most common presentation, doubles the risk of death. The alveolar macrophage is a sentinel pulmonary host defense cell, but the human alveolar macrophage in B. pseudomallei infection has never been studied. The objective of this study was to investigate the host-pathogen interaction of B. pseudomallei infection with the human alveolar macrophage and to determine the role of flagellin in modulating inflammasome-mediated pathways. We found that B. pseudomallei infects primary human alveolar macrophages but is gradually restricted in the setting of concurrent cell death. Electron microscopy revealed cytosolic bacteria undergoing division, indicating that B. pseudomallei likely escapes the alveolar macrophage phagosome and may replicate in the cytosol, where it triggers immune responses. In paired human blood monocytes, uptake and intracellular restriction of B. pseudomallei are similar to those observed in alveolar macrophages, but cell death is reduced. The alveolar macrophage cytokine response to B. pseudomallei is characterized by marked interleukin (IL)-18 secretion compared to monocytes. Both cytotoxicity and IL-18 secretion in alveolar macrophages are partially flagellin dependent. However, the proportion of IL-18 release that is driven by flagellin is greater in alveolar macrophages than in monocytes. These findings suggest differential flagellin-mediated inflammasome pathway activation in the human alveolar macrophage response to B. pseudomallei infection and expand our understanding of intracellular pathogen recognition by this unique innate immune lung cell.

Challenges and Opportunities for the Clinical Translation of Spatial Transcriptomics Technologies.

Background: The first spatially resolved transcriptomics platforms, GeoMx (Nanostring) and Visium (10x Genomics) were launched in 2019 and were recognized as the method of the year by Nature Methods in 2020. The subsequent refinement and expansion of these and other technologies to increase -plex, work with formalin-fixed paraffin-embedded tissue, and analyze protein in addition to gene expression have only added to their significance and impact on the biomedical sciences. In this perspective, we focus on two platforms for spatial transcriptomics, GeoMx and Visium, and how these platforms have been used to provide novel insight into kidney disease. The choice of platform will depend largely on experimental questions and design. The application of these technologies to clinically sourced biopsies presents the opportunity to identify specific tissue biomarkers that help define disease etiology and more precisely target therapeutic interventions in the future. Summary: In this review, we provide a description of the existing and emerging technologies that can be used to capture spatially resolved gene and protein expression data from tissue. These technologies have provided new insight into the spatial heterogeneity of diseases, how reactions to disease are distributed within a tissue, which cells are affected, and molecular pathways that predict disease and response to therapy. Key Message: The upcoming years will see intense use of spatial transcriptomics technologies to better define the pathophysiology of kidney diseases and develop novel diagnostic tests to guide personalized treatments for patients.

Can behaviorally inhibited preschoolers make friends?

Preschoolers who display extremely inhibited behavior are at risk for the development of anxiety disorders. However, behavioral inhibition (BI) is a multifaceted characteristic. Some children with BI are fearful when confronted by unfamiliar adults, peers, and objects; others are fearful when separated from their parents. In the present study, we examined specific features of BI that predicted observed friendship formation among preschoolers who are behaviorally inhibited. We also examined whether teacher ratings of classroom behaviors predicted friendship formation. Sixty highly inhibited children (35 female, Mage = 52.57 months) were observed during eight weekly free-play sessions with initially unfamiliar inhibited peers. Free-play periods occurred before weekly intervention sessions for children with BI and their parents. An observational protocol was developed to identify children who made a friend during the eight weekly sessions. Before the first session, different subtypes of BI were assessed by parents; preschool teachers assessed the children's classroom behaviors with familiar peers. Twenty-six children met the criteria for having made and kept a friend. Probit regression analyses revealed that parent ratings of BI among unfamiliar peers and teacher ratings of children's social anxiety before the intervention were associated with a decreased probability of making a friend. No evidence was found linking children's responses to the intervention and friendship formation. Results suggest that extremelyinhibited preschoolers are capable of making friends. Implications for future research and intervention efforts that focus on individual differences of children with BI are discussed. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

AA amyloidosis With Ig-Dominant Staining and Diagnostically Unusual Features.

Introduction: Although serum amyloid A (AA) amyloid may occasionally show nonspecific staining by immunofluorescence (IF), the correct diagnosis can usually be determined by integrating pathologic features and clinical scenario, and using AA amyloid immunohistochemistry (IHC) and/or mass spectrometry. A recent mass spectrometry-based study described false-positive Ig IF staining in a subset of AA amyloid cases. Methods: We sought to delineate clinicopathologic features of AA amyloid with Ig-dominant staining by using a retrospective review. Results: AA amyloid with Ig-dominant staining was identified in 10 patients from 5 institutions, representing 1.2% to 4% of AA amyloid kidney biopsies. Evidence of a monoclonal protein was documented in 0% to 2.7% of patients with AA amyloid screened for inclusion, but 30% of those with Ig-dominant staining. The patient population had equal sex distribution and presented at median age of 68.5 years with nephrotic proteinuria and kidney impairment. Etiologies of AA amyloid included injection drug use (30%), autoimmune disease (20%), and chronic infection (10%); 40% had no identified clinical association. On biopsy, heavy chain (co)dominant staining by IF (in 80%), discordant distribution in Ig staining (in 20%), tubulointerstitial nephritis (in 30%), and/or crescents (in 10%) were present. Two of 3 patients with paraproteinemia had concordant heavy and/or light chain dominant staining within the AA amyloid. Two cases were initially misdiagnosed as Ig-associated amyloidosis. Conclusion: We describe the morphologic spectrum of AA amyloidosis with Ig-dominant staining which may have clinical, laboratory, and pathologic overlap with amyloid light chain (AL), amyloid heavy chain, and heavy and light chain (AHL) amyloidosis.

The functional and anatomical characterization of three spinal output pathways of the anterolateral tract.

The nature of spinal output pathways that convey nociceptive information to the brain has been the subject of controversy. Here, we provide anatomical, molecular, and functional characterizations of two distinct anterolateral pathways: one, ascending in the lateral spinal cord, triggers nociceptive behaviors, and the other one, ascending in the ventral spinal cord, when inhibited, leads to sensorimotor deficits. Moreover, the lateral pathway consists of at least two subtypes. The first is a contralateral pathway that extends to the periaqueductal gray (PAG) and thalamus; the second is a bilateral pathway that projects to the bilateral parabrachial nucleus (PBN). Finally, we present evidence showing that activation of the contralateral pathway is sufficient for defensive behaviors such as running and freezing, whereas the bilateral pathway is sufficient for attending behaviors such as licking and guarding. This work offers insight into the complex organizational logic of the anterolateral system in the mouse.

HOPX-associated molecular programs control cardiomyocyte cell states underpinning cardiac structure and function.

Genomic regulation of cardiomyocyte differentiation is central to heart development and function. This study uses genetic loss-of-function human-induced pluripotent stem cell-derived cardiomyocytes to evaluate the genomic regulatory basis of the non-DNA-binding homeodomain protein HOPX. We show that HOPX interacts with and controls cardiac genes and enhancer networks associated with diverse aspects of heart development. Using perturbation studies in vitro, we define how upstream cell growth and proliferation control HOPX transcription to regulate cardiac gene programs. We then use cell, organoid, and zebrafish regeneration models to demonstrate that HOPX-regulated gene programs control cardiomyocyte function in development and disease. Collectively, this study mechanistically links cell signaling pathways as upstream regulators of HOPX transcription to control gene programs underpinning cardiomyocyte identity and function.

A quality improvement approach to improving recognition of Maori tamariki (children) and assessing barriers to culturally responsive care in a paediatric ward setting.

BACKGROUND: Health inequity persists in Aotearoa (New Zealand) and internationally amongst most indigenous peoples. To address these health inequities, countries need to contend with the ramifications of entrenched historical, cultural and systemic failures. Within Aotearoa part of the solution to rectifying persistent health inequities lies in shifting everyday healthcare practices towards a more culturally responsive, patient-centred approach that utilises Maori knowledge and principles. Although the need for culturally responsive services in healthcare settings is clearly evident, most practitioners struggle with the challenge of creating a culturally safe environment. Further to these challenges, there are issues related to accurate recognition of ethnicity within the time constraints of an overwrought hospital environment. Within this environment, the correct identification of ethnicity is a fundamental step in the process of moving towards culturally responsive and more inclusive care. METHOD: The research was concerned with indigenous Maori patients being consistently and correctly identified so that they might receive culturally appropriate interaction and treatment. The research specifically focused on the impact of introducing a customised sticker prompt on the front cover of clinical notes of Maori tamariki (children) to assist with correct ethnicity identification. Surveys were conducted on the paediatric ward over a 3-week period, prior to and during the intervention to evaluate the effect of the customised stickers. This study sought to (1) assess the efficacy of a sticker to improve recognition of Maori tamariki (children), (2) examine key barriers to identifying ethnicity and (3) identify wider impacts of a sticker prompt on clinical practice. RESULTS: Results showed wide ranging positive impacts on clinical practice and culturally responsive care. Sixty-four per cent of participants indicated that the stickers were a useful tool to improve identification of Maori tamariki. Respondents reported increased accuracy of identifying patients by ethnicity, as well as improved awareness of existing ethnicity documentation, and increased engagement regarding cultural needs and ethnicity. CONCLUSIONS: This study identified that sticker prompts are a useful tool for healthcare workers to improve recognition and awareness of ethnicity and to increase dialogue around cultural needs. The stickers led to increased consideration of the wider elements of holistic wellbeing and therefore improved culturally responsive care for Maori tamariki.

Lupus IgA1 autoantibodies synergize with IgG to enhance pDC responses to RNA-containing immune complexes.

Autoantibodies to nuclear antigens are hallmarks of the autoimmune disease systemic lupus erythematosus (SLE) where they contribute to pathogenesis. However, there remains a gap in our knowledge regarding how different isotypes of autoantibodies contribute to disease, including the production of the critical type I interferon (IFN) cytokines by plasmacytoid dendritic cells (pDCs) in response to immune complexes (ICs). We focused on IgA, which is the second most prevalent isotype in serum, and along with IgG is deposited in glomeruli in lupus nephritis. Here, we show that individuals with SLE have IgA autoantibodies against most nuclear antigens, correlating with IgG against the same antigen. We investigated whether IgA autoantibodies against a major SLE autoantigen, Smith ribonucleoproteins (Sm/RNPs), play a role in IC activation of pDCs. We found that pDCs express the IgA-specific Fc receptor, FcαR, and there was a striking ability of IgA1 autoantibodies to synergize with IgG in RNA-containing ICs to generate robust pDC IFNα responses. pDC responses to these ICs required both FcαR and FcγRIIa, showing a potent synergy between these Fc receptors. Sm/RNP IC binding to and internalization by pDCs were greater when ICs contained both IgA1 and IgG. pDCs from individuals with SLE had higher binding of IgA1-containing ICs and higher expression of FcαR than pDCs from healthy control individuals. Whereas pDC FcαR expression correlated with blood ISG signature in SLE, TLR7 agonists, but not IFNα, upregulated pDC FcαR expression in vitro. Together, we show a new mechanism by which IgA1 autoantibodies contribute to SLE pathogenesis.

Anti-GSTT1 antibodies and Null genotype correlate with histological changes of antibody mediated rejection in kidney transplantation.

BACKGROUND: The presence of anti-Glutathione S-transferase T1 (GSTT1) antibodies (abs) has been hypothesized as a pathogenic contributor in antibody-mediated rejection (AMR). METHODS: We aimed to evaluate the relationship between genetic variants of GSTT1, anti-GSTT1 abs and AMR in a cohort of 87 kidney transplant (KTx) patients using Immucor's non-HLA Luminex assay. Patients were classified according to biopsy-proven AMR and HLA-DSA status: AMR with positive anti-HLA-DSAs (AMR/DSA+, n = 29), AMR but no detectable anti-HLA-DSAs (AMR/DSA-, n = 28) and control patients with stable allograft function and no evidence of rejection (n = 30). RESULTS: At an MFI cut-off of 3000, the overall prevalence of anti-GSTT1 abs was 18.3%. The proportion of patients with anti-GSTT1 abs was higher in the AMR/DSA- group (25%), compared to the control (13.3%) and AMR/DSA+ group (3.4%) (p = 0.06). Among patients with anti-GSTT1 abs, the MFI was higher in AMR/DSA- and GSTT1-Null patients. Of 81 patients who underwent GSTT1 genotyping, 19.8% were homozygotes for the null allele (GSTT1-Null). GSTT1-Null status in the transplant recipients was associated with the development of anti-GSTT1 abs (OR, 4.49; 95%CI, 1.2-16.7). In addition, GSTT1-Null genotype (OR 26.01; 95%CI, 1.63-404) and anti-GSTT1 ab positivity (OR 14.8; 95%CI, 1.1-190) were associated with AMR. Within AMR/DSA- patients, the presence of anti-GSTT1 abs didn't confer a higher risk of failure within the study observation period. CONCLUSION: The presence of anti-GSTT1 abs and GSTT1-Null genotype is associated with AMR, but do not appear to lead to accelerated graft injury in this cohort of early allograft injury changes, with a limited period of follow-up.

Loss of Sec-1 Family Domain-Containing 1 (scfd1) Causes Severe Cardiac Defects and Endoplasmic Reticulum Stress in Zebrafish.

Dilated cardiomyopathy (DCM) is a common heart muscle disorder that frequently leads to heart failure, arrhythmias, and death. While DCM is often heritable, disease-causing mutations are identified in only ~30% of cases. In a forward genetic mutagenesis screen, we identified a novel zebrafish mutant, heart and head (hahvcc43), characterized by early-onset cardiomyopathy and craniofacial defects. Linkage analysis and next-generation sequencing identified a nonsense variant in the highly conserved scfd1 gene, also known as sly1, that encodes sec1 family domain-containing 1. Sec1/Munc18 proteins, such as Scfd1, are involved in membrane fusion regulating endoplasmic reticulum (ER)/Golgi transport. CRISPR/Cas9-engineered scfd1vcc44 null mutants showed severe cardiac and craniofacial defects and embryonic lethality that recapitulated the phenotype of hahvcc43 mutants. Electron micrographs of scfd1-depleted cardiomyocytes showed reduced myofibril width and sarcomere density, as well as reticular network disorganization and fragmentation of Golgi stacks. Furthermore, quantitative PCR analysis showed upregulation of ER stress response and apoptosis markers. Both heterozygous hahvcc43 mutants and scfd1vcc44 mutants survived to adulthood, showing chamber dilation and reduced ventricular contraction. Collectively, our data implicate scfd1 loss-of-function as the genetic defect at the hahvcc43 locus and provide new insights into the role of scfd1 in cardiac development and function.

Identification of a convergent spinal neuron population that encodes itch.

Itch is a protective sensation that drives scratching. Although specific cell types have been proposed to underlie itch, the neural circuit basis for itch remains unclear. Here, we used two-photon Ca2+ imaging of the dorsal horn to visualize the neuronal populations that are activated by itch-inducing agents. We identify a convergent population of spinal neurons that is defined by the expression of GRPR. Moreover, we discover that itch is conveyed to the brain via GRPR-expressing spinal output neurons that target the lateral parabrachial nucleus. Further, we show that nalfurafine, a clinically effective kappa opioid receptor agonist, relieves itch by inhibiting GRPR spinoparabrachial neurons. Finally, we demonstrate that a subset of GRPR spinal neurons show persistent, cell-intrinsic Ca2+ oscillations. These experiments provide the first population-level view of the spinal neurons that respond to pruritic stimuli, pinpoint the output neurons that convey itch to the brain, and identify the cellular target of kappa opioid receptor agonists for the inhibition of itch.

Organ-specific immunity: A tissue analysis framework for investigating local immune responses to SARS-CoV-2.

Local immune activation at mucosal surfaces, mediated by mucosal lymphoid tissues, is vital for effective immune responses against pathogens. While pathogens like severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can spread to multiple organs, patients with coronavirus disease 2019 (COVID-19) primarily experience inflammation and damage in their lungs. To investigate this apparent organ-specific immune response, we develop an analytical framework that recognizes the significance of mucosal lymphoid tissues. This framework combines histology, immunofluorescence, spatial transcript profiling, and mathematical modeling to identify cellular and gene expression differences between the lymphoid tissues of the lung and the gut and predict the determinants of those differences. Our findings indicate that mucosal lymphoid tissues are pivotal in organ-specific immune response to SARS-CoV-2, mediating local inflammation and tissue damage and contributing to immune dysfunction. The framework developed here has potential utility in the study of long COVID and may streamline biomarker discovery and treatment design for diseases with differential pathologies at the organ level.

Testing reciprocal associations between child anxiety and parenting across early interventions for inhibited preschoolers.

BACKGROUND: Given the robust evidence base for the efficacy of evidence-based treatments targeting youth anxiety, researchers have advanced beyond efficacy outcome analysis to identify mechanisms of change and treatment directionality. Grounded in developmental transactional models, interventions for young children at risk for anxiety by virtue of behaviorally inhibited temperament often target parenting and child factors implicated in the early emergence and maintenance of anxiety. In particular, overcontrolling parenting moderates risk for anxiety among highly inhibited children, just as child inhibition has been shown to elicit overcontrolling parenting. Although longitudinal research has elucidated the temporal unfolding of factors that interact to place inhibited children at risk for anxiety, reciprocal transactions between these child and parent factors in the context of early interventions remain unknown. METHOD: This study addresses these gaps by examining mechanisms of change and treatment directionality (i.e., parent-to-child vs. child-to-parent influences) within a randomized controlled trial comparing two interventions for inhibited preschoolers (N = 151): the multicomponent Turtle Program ('Turtle') and the parent-only Cool Little Kids program ('CLK'). Reciprocal relations between parent-reported child anxiety, observed parenting, and parent-reported accommodation of child anxiety were examined across four timepoints: pre-, mid-, and post-treatment, and one-year follow-up (NCT02308826). RESULTS: Hypotheses were tested via latent curve models with structured residuals (LCM-SR) and latent change score (LCS) models. LCM-SR results were consistent with the child-to-parent influences found in previous research on cognitive behavioral therapy (CBT) for older anxious youth, but only emerged in Turtle. LCS analyses revealed bidirectional effects of changes in parent accommodation and child anxiety during and after intervention, but only in Turtle. CONCLUSION: Our findings coincide with developmental transactional models, suggesting that the development of child anxiety may result from child-to-parent influences rather than the reverse, and highlight the importance of targeting parent and child factors simultaneously in early interventions for young, inhibited children.