Biology subjects

Kulkarni, H. S.

Publications and source records attributed to Kulkarni, H. S..

9 recordsLinked to original sources

bioRxiv2026

Kinetics of local C3 production orchestrates neutrophil recruitment in lung injury

Complement component 3 (C3) is crucial for host defense against bacteria. While the liver is the primary source of circulating C3, local C3 production at barrier surfaces such as the lung is key in early responses. Yet, how local complement-mediated responses are initiated at mucosal barriers is unknown. This study investigates the kinetics and necessity of lung-derived C3 during the initial hours of an infection. Using models of bacterial pneumonia in ex vivo-perfused human lungs and mice deficient in liver-derived C3, we demonstrate that intrapulmonary C3 production and activation precedes the accumulation of circulating C3 into the bronchoalveolar space. Utilizing mice deficient in lung-derived C3, we demonstrate that epithelial cell-derived C3 is required for early neutrophil recruitment in pneumonia. Transcriptomic and proteomic analyses reveal that neutrophil chemotactic pathways such as C5a and CXCL2 depend on lung epithelial cell-derived C3. These findings demonstrate how lung epithelial-derived C3 influences early mucosal responses to infection via both canonical (direct) and non-canonical (indirect) pathways. SUMMARYAlburquerque et al show an initial, entirely local phase of complement-mediated mucosal protection before a subsequent, systemic response occurs in the setting of barrier disruption. Their work suggests that complement component C3 derived locally at a barrier from the epithelium influences early responses to infection by recruiting neutrophils via multiple pathways independent of circulating C3.

immunology↗

bioRxiv2026

Mucosally sourced complement factor B modulates the host response to colitis

Distinct host factors maintain intestinal homeostasis but are incompletely understood. The complement system is primarily liver-derived and serum-operative. However, there is growing recognition for complement-mediated host defense at mucosal surfaces. The alternative pathway, which is constitutively active at low levels and amplifies complement activation independent of antibodies, requires Complement Factor B (CFB). Despite its evolutionary conservation, the spatial, cellular, and functional roles of CFB in the intestine are poorly understood. Here, we show that CFB is produced in the human colon and is increased in patients with active inflammatory bowel disease. To isolate the role of local CFB in mucosal responses, we interrogated a mouse strain that has no circulating, liver-derived CFB but retains intact CFB expression in the gut. Global CFB-deficient mice succumb to colitis compared to these liver-specific knockout mice, suggesting that locally synthesized CFB mitigates colitis. Single-cell analyses identify enterocytes and fibroblasts as key CFB producers in the gut. Compartment-specific deletion of CFB from epithelial or stromal cells abrogates mucosal protection independent of circulating levels, which corroborates with pharmacological CFB inhibition. These findings redefine complement in the intestine as a locally regulated mucosal defense system and establish gut-derived CFB as a critical determinant of intestinal homeostasis. BRIEF SUMMARYThe role of local immune mediators in gut mucosal immune responses is still not entirely understood. In this study, we demonstrate a novel role for complement protein Factor B, a key component of the alternative pathway, which is locally sourced through epithelial and stromal cells. In vivo modeling of impaired local Factor B synthesis results in worse colitis, revealing a key role for mucosal sourced components of the alternative pathway.

immunology↗

bioRxiv2024

Impaired complement regulation drives chronic lung allograft dysfunction after lung transplantation.

A greater understanding of chronic lung allograft dysfunction (CLAD) pathobiology, the primary cause of mortality after lung transplantation, is needed to improve outcomes. The complement system links innate to adaptive immune responses and is activated early post-lung transplantation to form the C3 convertase, a critical enzyme that cleaves the central complement component C3. We hypothesized that LTx recipients with a genetic predisposition to enhanced complement activation have worse CLAD-free survival mediated through increased adaptive alloimmunity. We interrogated a known functional C3 polymorphism (C3R102G) that increases complement activation through impaired C3 convertase inactivation in two independent LTx recipient cohorts. C3R102G, identified in at least one out of three LTx recipients, was associated with worse CLAD-free survival, particularly in the subset of recipients who developed donor-specific antibodies (DSA). In a mouse orthotopic lung transplantation model, impaired recipient complement regulation resulted in more severe obstructive airway lesions when compared to wildtype controls, despite only moderate differences in graft-infiltrating effector T cells. Impaired complement regulation promoted the intragraft accumulation of memory B cells and antibody-secreting cells, resulting in increased DSA levels. In summary, genetic predisposition to complement activation is associated with B cell activation and worse CLAD-free survival. BRIEF SUMMARYLung transplant recipients genetically predisposed to impaired complement regulation demonstrate worse chronic rejection-free survival. This phenotype is associated with intragraft B cell-activation and donor-specific antibodies.

immunology↗

bioRxiv2024

The C3-C3aR axis modulates trained immunity in alveolar macrophages

Complement protein C3 is crucial for immune responses in mucosal sites such as the lung, where it aids in microbe elimination and enhances inflammation. While trained immunity - enhanced secondary responses of innate immune cells after prior exposure - is well-studied, the role of the complement system in trained immune responses remains unclear. We investigated the role of C3 in trained immunity and found that alveolar macrophage C3 and C3aR1 expression increased in humans after an intranasal exposure to a training stimulus. In vivo, trained wild-type mice showed significantly elevated pro-inflammatory cytokines and increased C3a levels upon a second stimulus. Ex vivo, trained C3-deficient alveolar macrophages (AMs) displayed reduced chemokine and cytokine output as well as impaired phagocytosis and reactive oxygen species (ROS) production compared to wildtype AMs. Real-time confocal microscopy of live, intact mouse alveoli revealed that AMs internalize C3 rapidly after alveolar microinstillation, as compared to C3a. Correspondingly, the blunted cytokine output was restored by exogenous C3 but not by C3a. Inhibiting C3aR, both pharmacologically and with a genetic C3aR knockout, prevented this restoration, indicating the necessity of C3aR engagement. Mechanistically, trained WT AMs demonstrated enhanced glycolytic activity compared to C3-deficient AMs - a defect corrected by exogenous C3 in a C3aR-dependent manner. These findings reveal that C3 modulates trained immunity in AMs through C3aR signaling and highlight a novel role for C3 in trained immunity.

immunology↗

bioRxiv2024

Characteristics of human donor lungs utilized for research

IntroductionMany fundamental discoveries have occurred using primary cells from deceased donor lungs. These cells respond differently to injury when there are underlying co-morbidities like diabetes mellitus, hypertension, aging and exposures to cigarette smoke, cocaine and chronic alcohol use. However, the prevalence of these characteristics in donor lungs utilized for research is currently unknown. MethodsThis retrospective cohort study procured data of lung transplant donors from Mid-America Transplant from January 2017 until July 2023. The donors were characterized based on lung utilization into three groups - lungs used for research, lungs used for transplant, and lungs not recovered from donors for either research or transplantation. ResultsThe mean age of donors whose lungs were utilized for research was 41{+/-}18 years. 25% of them were expanded criteria donors (ECD) while 10% of the donors in the transplant cohort were ECD. 14% of the donors whose lungs were utilized for research had history of diabetes compared to 8% of donors whose lungs were transplanted. A quarter of the research donor population had positive history of cigarette use within the preceding 20 years. At least 40% of donors had a positive history of non-intravenous drug use, of whom a majority had a history of continued non-intravenous drug use. ConclusionsNo strict selection criteria or protocols exist when human donor lungs are obtained for ex-vivo research. There is a high prevalence of diabetes mellitus, history of smoking and non-intravenous drug use along with older age distribution in donors whose lungs used are for research.

immunology↗

bioRxiv2022

Lung epithelial cell-derived C3 protects against pneumonia-induced lung injury

The complement component C3 is a fundamental plasma protein for host defense. However, recent work has demonstrated the critical importance of local C3 expression in cell survival. Here we analyzed the effects of local versus peripheral sources of C3 expression in a model of bacterial pneumonia. While mice with global C3 deficiency had severe pneumonia-induced lung injury, those deficient in liver-deficient C3 remain protected, comparable to wildtype mice. Human lung transcriptome analysis showed secretory epithelial cells are a major source of C3. Mice with a C3 gene ablation from lung epithelial cells had worse pulmonary injury compared to wild type, despite maintaining normal circulating C3 levels. Finally, in human cellular and mouse pneumonia models, we show that C3 reduces epithelial cell death mediated through the alternative pathway component Factor B. Thus, our findings suggest that a locally-derived C3-Factor B pathway protects the lung mucosal barrier. One Sentence SummaryLung-derived C3 mitigates severe bacterial pneumonia suggesting a novel cytoprotective role at mucosal barrier surfaces independent of circulating C3.

immunology↗

bioRxiv2022

Reprogramming Alveolar Macrophage Responses to TGF-β Reveals CCR2+ Monocyte Activity that Promotes Bronchiolitis Obliterans Syndrome

Bronchiolitis obliterans syndrome (BOS) is a major impediment to lung transplant survival and is generally resistant to medical therapy. Extracorporeal photophoresis (ECP) is an immunomodulatory therapy that shows promise in stabilizing BOS patients but its mechanisms of action are unclear. In a mouse lung transplant model, we show that ECP blunts alloimmune responses and inhibits BOS through lowering airway TGF-{beta} bioavailability without altering its expression. Surprisingly, ECP-treated leukocytes are engulfed primarily by alveolar macrophages (AM), which become reprogrammed to become less responsive to TGF-{beta} and reduce TGF-{beta} bioavailability through secretion of the TGF-{beta} antagonist Decorin. In untreated recipients, high airway TGF-{beta} activity stimulates AM to express CCL2 leading to CCR2+ monocyte-driven BOS development. Moreover, we find TGF-{beta} receptor 2-dependent differentiation of CCR2+ monocytes is required for the generation of monocyte-derived AM, which in turn promote BOS by expanding tissue-resident memory CD8+ T cells that inflict airway injury through Blimp-1-mediated Granzyme B expression. Thus, through studying the effects of ECP, we have identified an AM functional plasticity that controls a TGF-{beta}-dependent network, which couples CCR2+ monocyte recruitment and differentiation to alloimmunity and BOS. Alveolar macrophage plasticity can be harnessed to prevent Bronchiolitis Obliterans Syndrome.

immunology↗

bioRxiv2021

Increased complement activation is a distinctive feature of severe SARS-CoV-2 infection.

Complement activation has been implicated in the pathogenesis of severe SARS-CoV-2 infection. However, it remains to be determined whether increased complement activation is a broad indicator of critical illness (and thus, no different in COVID-19). It is also unclear which pathways are contributing to complement activation in COVID-19, and, if complement activation is associated with certain features of severe SARS-CoV-2 infection, such as endothelial injury and hypercoagulability. To address these questions, we investigated complement activation in the plasma from patients with COVID-19 prospectively enrolled at two tertiary care centers. We compared our patients to two non-COVID cohorts: (a) patients hospitalized with influenza, and (b) patients admitted to the intensive care unit (ICU) with acute respiratory failure requiring invasive mechanical ventilation (IMV). We demonstrate that circulating markers of complement activation (i.e., sC5b-9) are elevated in patients with COVID-19 compared to those with influenza and to patients with non-COVID-19 respiratory failure. Further, the results facilitate distinguishing those who are at higher risk of worse outcomes such as requiring ICU admission, or IMV. Moreover, the results indicate enhanced activation of the alternative complement pathway is most prevalent in patients with severe COVID-19 and is associated with markers of endothelial injury (i.e., Ang2) as well as hypercoagulability (i.e., thrombomodulin and von Willebrand factor). Our findings identify complement activation to be a distinctive feature of COVID-19, and provide specific targets that may be utilized for risk prognostication, drug discovery and personalized clinical trials. SUMMMARYComplement has been implicated in COVID-19. However, whether this is distinctive of COVID-19 remains unanswered. Ma et al report increased complement activation in COVID-19 compared to influenza and non-COVID respiratory failure, and demonstrate alternative pathway activation as a key marker of multiorgan failure and death.

immunology↗

bioRxiv2020

Circulating Mitochondrial DNA is an Early Indicator of Severe Illness and Mortality from COVID-19

Mitochondrial DNA (MT-DNA) are intrinsically inflammatory nucleic acids released by damaged solid organs. Whether the appearance of cell-free MT-DNA is linked to poor COVID-19 outcomes remains undetermined. Here, we quantified circulating MT-DNA in prospectively collected, cell-free plasma samples from 97 subjects with COVID-19 at the time of hospital presentation. Circulating MT-DNA were sharply elevated in patients who eventually died, required ICU admission or intubation. Multivariate regression analysis revealed that high circulating MT-DNA levels is an independent risk factor for all of these outcomes after adjusting for age, sex and comorbidities. Additionally, we found that circulating MT-DNA has a similar or superior area-under-the curve when compared to clinically established measures of systemic inflammation, as well as emerging markers currently of interest as investigational targets for COVID-19 therapy. These results show that high circulating MT-DNA levels is a potential indicator for poor COVID-19 outcomes.

immunology↗