Adaptive immunity to fungi.

Only a handful of the more than 100,000 fungal species on our planet cause disease in humans, yet the number of life-threatening fungal infections in patients has recently skyrocketed as a result of advances in medical care that often suppress immunity intensely. This emerging crisis has created pressing needs to clarify immune defense mechanisms against fungi, with the ultimate goal of therapeutic applications. Herein, we describe recent insights in understanding the mammalian immune defenses deployed against pathogenic fungi. The review focuses on adaptive immune responses to the major medically important fungi and emphasizes how dendritic cells and subsets in various anatomic compartments respond to fungi, recognize their molecular patterns, and signal responses that nurture and shape the differentiation of T cell subsets and B cells. Also emphasized is how the latter deploy effector and regulatory mechanisms that eliminate these nasty invaders while also constraining collateral damage to vital tissue.

The skin I live in: Pathogenesis of white-nose syndrome of bats.

The emergence of white-nose syndrome (WNS) in North America has resulted in mass mortalities of hibernating bats and total extirpation of local populations. The need to mitigate this disease has stirred a significant body of research to understand its pathogenesis. Pseudogymnoascus destructans, the causative agent of WNS, is a psychrophilic (cold-loving) fungus that resides within the class Leotiomycetes, which contains mainly plant pathogens and is unrelated to other consequential pathogens of animals. In this review, we revisit the unique biology of hibernating bats and P. destructans and provide an updated analysis of the stages and mechanisms of WNS progression. The extreme life history of hibernating bats, the psychrophilic nature of P. destructans, and its evolutionary distance from other well-characterized animal-infecting fungi translate into unique host-pathogen interactions, many of them yet to be discovered.

Sensitization with Fungal Protease Allergen Establishes Long-Lived, Allergenic Th Cell Memory in the Lung.

Allergic asthma is a chronic inflammatory disease that affects millions of individuals worldwide. Exposure to allergens produced by a variety of otherwise harmless microbes, including fungi, predisposes individuals to immunopathologic disease upon subsequent encounters with allergen. We developed a mouse model that employs a purified protease produced by Aspergillus (Asp f 13) to investigate the contributions of CD4+ Th cells to recurrent lung inflammation. Notably, memory CD4+ T cells enhanced the eosinophil response of sensitized/rechallenged animals. In addition, memory CD4+ T cells maintained allergenic features, including expression of GATA-binding protein 3 and IL-5. Th2 memory T cells persisted in the peribronchiolar interstitium of the lung and expressed markers of tissue residence, such as CD69, CCR8, and IL-33R. Lastly, we identified a peptide epitope contained within Asp f 13 and generated a peptide-MHC class II tetramer. Using these tools, we further demonstrated the durability and exquisite sensitivity of memory T cells in promoting lung eosinophilia. Our data highlight important features of memory T cells that strengthen the notion that memory T cells are principal drivers of eosinophilic disease in murine models of allergic sensitization and episodic airway inflammation.

Vaccination with O-linked Mannans Protects against Systemic Candidiasis through Innate Lymphocyte Populations.

Candida spp. are the fourth leading cause of bloodstream infections in hospitalized patients and the most common cause of invasive fungal infection. No vaccine against Candida spp. or other fungal pathogens of humans is available. We recently discovered the Blastomyces Dectin-2 ligand endoglucanase 2 that harbors antigenic and adjuvant functions and can function as a protective vaccine against that fungus. We also reported that the adjuvant activity, which is mediated by O-mannans decorating the C terminus of Blastomyces Dectin-2 ligand endoglucanase 2, can augment peptide Ag-induced vaccine immunity against heterologous agents, including Cryptococcus, Candida, and influenza. In this article, we report that the O-linked mannans alone, in the absence of any antigenic peptide, can also protect against systemic candidiasis, reducing kidney fungal load and increasing survival in a Dectin-2-dependent manner. We found that this long-term glycan-induced protection is mediated by innate lymphocyte populations including TCR-γδ+ T cells, innate lymphoid cells, and NK cells that subsequently activate and release reactive oxygen species from neutrophils and monocytes. Our findings suggest that Blastomyces O-mannan displayed by Eng2 induces a form of protective trained immunity mediated by innate lymphocyte populations.

T cell receptor cross-reactivity between similar foreign and self peptides influences naive cell population size and autoimmunity.

T cell receptor (TCR) cross-reactivity between major histocompatibility complex II (MHCII)-binding self and foreign peptides could influence the naive CD4(+) T cell repertoire and autoimmunity. We found that nonamer peptides that bind to the same MHCII molecule only need to share five amino acids to cross-react on the same TCR. This property was biologically relevant because systemic expression of a self peptide reduced the size of a naive cell population specific for a related foreign peptide by deletion of cells with cross-reactive TCRs. Reciprocally, an incompletely deleted naive T cell population specific for a tissue-restricted self peptide could be triggered by related microbial peptides to cause autoimmunity. Thus, TCR cross-reactivity between similar self and foreign peptides can reduce the size of certain foreign peptide-specific T cell populations and might allow T cell populations specific for tissue-restricted self peptides to cause autoimmunity after infection.

SLAMF1 Is Dispensable for Vaccine-Induced T Cell Development but Required for Resistance to Fungal Infection.

Homotypic signaling lymphocyte activation molecule (SLAM) receptor-ligand cell surface interactions between myeloid and lymphoid cells regulate innate and adaptive immune responses. In this article, we report that SLAMF1 is indispensable for host resistance to primary and vaccine-induced protection against fungal infection. Because vaccine immunity is dependent on cell-mediated immunity, we investigated the development of Ag-specific T cells. We studied the T cell-intrinsic and -extrinsic role of SLAMF1. We generated SLAMF1-/- TCR transgenic mice and analyzed the responses of adoptively transferred T cells. We also tracked endogenous Ag-specific T cells by using a tetramer. Intrinsic and extrinsic SLAMF1 signaling was dispensable for the development of antifungal Th1 and Th17 cells, which are requisite for the acquisition of vaccine-induced immunity. Despite intact T cell development, vaccinated SLAMF1-/- mice failed to control fungal infection. Failed accumulation of Ag-specific T cells in the lung on infection of vaccinated mice was due to uncontrolled early infection and inflammation, revealing a role for SLAMF1 in innate host immunity.

Structural basis of Blastomyces Endoglucanase-2 adjuvancy in anti-fungal and -viral immunity.

The development of safe subunit vaccines requires adjuvants that augment immunogenicity of non-replicating protein-based antigens. Current vaccines against infectious diseases preferentially induce protective antibodies driven by adjuvants such as alum. However, the contribution of antibody to host defense is limited for certain classes of infectious diseases such as fungi, whereas animal studies and clinical observations implicate cellular immunity as an essential component of the resolution of fungal pathogens. Here, we decipher the structural bases of a newly identified glycoprotein ligand of Dectin-2 with potent adjuvancy, Blastomyces endoglucanase-2 (Bl-Eng2). We also pinpoint the developmental steps of antigen-specific CD4+ and CD8+ T responses augmented by Bl-Eng2 including expansion, differentiation and tissue residency. Dectin-2 ligation led to successful systemic and mucosal vaccination against invasive fungal infection and Influenza A infection, respectively. O-linked glycans on Bl-Eng2 applied at the skin and respiratory mucosa greatly augment vaccine subunit- induced protective immunity against lethal influenza and fungal pulmonary challenge.

Impact of an Emergency Department Saturation Tool on a Pediatric Hospital's Capacity Management Policy.

OBJECTIVE: We sought to describe how the Emergency Department Work Index (EDWIN) saturation tool (1) correlates with PED overcrowding during a capacity management activation policy, known internally as Purple Alert and (2) compare overall hospital-wide capacity metrics on days in which the alert was instituted versus days it was not. METHODS: This study was conducted between January 1, 2017 and December 31, 2019 in a 30-bed academic quaternary care, urban PED within a university hospital. The EDWIN tool was implemented in January 2019 and objectively measured the busyness of the PED. To determine correlation with overcrowding, EDWIN scores were calculated at alert initiation. Mean alert hours per month were plotted on a control chart before and after EDWIN implementation. We also compared daily numbers of PED visits, inpatient admissions, and patients left without being seen (LWBS) for days with and without alert initiation to assess whether or not Purple Alert correlated with high PED usage. RESULTS: During the study period, the alert was activated a total of 146 times; 43 times after EDWIN implementation. Mean EDWIN score was 2.5 (SD 0.5, min 1.5, max 3.8) at alert initiation. There were no alert occurrences for EDWIN scores less than 1.5 (not overcrowded). There was no statistically significant difference for mean alert hours per month before and after EDWIN was instituted (21.4 vs 20.2, P = 0.08). Mean numbers of PED visits, inpatient admissions, and patients left without being seen were higher on days with alert activation ( P < 0.001 for all). CONCLUSIONS: The EDWIN score correlated with PED busyness and overcrowding during alert activation and correlated with high PED usage. Future studies could include implementing a real-time Web-based EDWIN score as a prediction tool to prevent overcrowding and verifying EDWIN generalizability at other PED sites.

Treatment Guideline Nonadherence Pretransport Associated With Need for Higher Level of Care in Children Transferred to a Pediatric Tertiary Care Center for Status Epilepticus.

OBJECTIVES: We sought to investigate the association between adherence to the American Epilepsy Society (AES) 2016 guidelines for management of convulsive status epilepticus (SE) and clinical outcomes among children requiring interhospital transport for SE. We hypothesized that pretransport guideline nonadherence would be associated with needing higher level of care posttransfer. METHODS: This was a retrospective cohort study of children aged 30 days to 18 years transferred to our pediatric tertiary center from 2017 to 2019 for management of SE. Their care episodes were classified as 2016 American Epilepsy Society guideline adherent or nonadherent. There were 40 referring hospitals represented in this cohort. RESULTS: Of 260 care episodes, 55 (21%) were guideline adherent, 184 (71%) were guideline nonadherent, and 21 (8%) had insufficient data to determine guideline adherence. Compared with the adherent group, patients in the nonadherent care group had longer hospitalizations (32 hours [17-68] vs 21 hours [7-48], P = 0.006), were more likely to require intensive care unit admission (47% vs 31%), and less likely to be discharged home from the emergency department (16% vs 35%; χ 2 test, P = 0.01). Intubation rates did not differ significantly between groups (25% vs 18%, P = 0.37). When we fit a multivariable model to adjust for confounding variables, guideline nonadherence was associated with need for higher level of care (odds ratio, 2.04; 95% confidence interval, 1.04-3.99). Treatment guideline adherence did not improve over the 3-year study period (2017: 22%, 2018: 19%, 2019: 29% [χ 2 test for differences between any 2 years, P = 0.295]). CONCLUSIONS: Guideline nonadherence pretransport was associated with longer hospitalizations and need for higher level of care among children transferred for SE at our institution. These findings suggest a need to improve SE guideline adherence through multifaceted quality improvement efforts targeting both the prehospital and community hospital settings.

Characterization of antifungal C-type lectin receptor expression on murine epithelial and endothelial cells in mucosal tissues.

Our data reveal that selection of enzymes for generating single cell suspensions from murine tissues influences detection of surface expression of antifungal CLRs. Using a method that most preserves receptor expression, we show that non-myeloid expression of antifungal CLRs is limited to MelLec on endothelial cells in murine mucosal tissues.

CARD9-Associated Dectin-1 and Dectin-2 Are Required for Protective Immunity of a Multivalent Vaccine against Coccidioides posadasii Infection.

Coccidioides species are fungal pathogens that can cause a widely varied clinical manifestation from mild pulmonary symptom to disseminated, life-threatening disease. We have previously created a subunit vaccine by encapsulating a recombinant coccidioidal Ag (rCpa1) in glucan-chitin particles (GCPs) as an adjuvant-delivery system. The GCP-rCpa1 vaccine has shown to elicit a mixed Th1 and Th17 response and confers protection against pulmonary coccidioidomycosis in mice. In this study, we further delineated the vaccine-induced protective mechanisms. Depletion of IL-17A in vaccinated C57BL/6 mice prior to challenge abrogated the protective efficacy of GCP-rCpa1 vaccine. Global transcriptome and Ingenuity Pathway Analysis of murine bone marrow-derived macrophages after exposure to this vaccine revealed the upregulation of proinflammatory cytokines (TNF-α, IL-6, and IL-1ß) that are associated with activation of C-type lectin receptors (CLR) Dectin-1- and Dectin-2-mediated CARD9 signaling pathway. The GCP formulation of rCpa1 bound soluble Dectin-1 and Dectin-2 and triggered ITAM signaling of corresponding CLR reporter cells. Furthermore, macrophages that were isolated from Dectin-1 -/-, Dectin-2 -/-, and CARD9 -/- mice significantly reduced production of inflammatory cytokines in response to the GCP-rCpa1 vaccine compared with those of wild-type mice. The GCP-rCpa1 vaccine had significantly reduced protective efficacy in Dectin-1 -/-, Dectin-2 -/-, and CARD9 -/- mice that showed decreased acquisition of Th cells in Coccidioides-infected lungs compared with vaccinated wild-type mice, especially Th17 cells. Collectively, we conclude that the GCP-rCpa1 vaccine stimulates a robust Th17 immunity against Coccidioides infection through activation of the CARD9-associated Dectin-1 and Dectin-2 signal pathways.

Interhospital Transport of Children With Peripheral Venous Catheters by Private Vehicle: A Mixed Methods Assessment.

BACKGROUND: Many children seeking emergency care at community hospitals require transport to tertiary centers for definitive management. Interhospital transport via ambulance versus patient's own vehicle (POV) are 2 possible modes of transport; however, presence of a peripheral venous catheter (PIV) can determine transport by ambulance. Caregiver satisfaction, patient comfort, and PIV complications related to POV transport have not been described. OBJECTIVE: The aims of the study were to examine caregivers' satisfaction and perceptions of POV transport in children with/without PIVs and to assess PIV-related complications during transport. METHODS: We performed a mixed-methods, prospective cohort study of children who presented with low-acuity conditions to a community hospital and subsequently required transfer to a pediatric tertiary center. Caregivers of patients with/without PIVs were given the choice of transport by POV or ambulance. Surveys completed after transport used dichotomous, 5-point Likert scale, and open-ended responses to assess satisfaction, perceptions, and PIV-related complications. Responses were quantitatively and qualitatively analyzed accordingly. The receiving hospital assessed PIV integrity. RESULTS: Sixty-nine of 78 eligible patients were enrolled; of those, 67 (97%) elected transport by POV and 55 (82%) completed surveys. Most caregivers had positive responses related to satisfaction, comfort, and safety. Results did not differ significantly between those with/without PIVs. The majority (96%) would choose POV transport again. There were no reported PIV complications; all PIVs were functional upon arrival. Qualitative analysis identified themes of comfort, convenience, and efficiency. CONCLUSIONS: In select scenarios, interfacility transport by POV is preferred by families and doing so with a saline-locked PIV does not result in complications.

Infectious particle identity determines dissemination and disease outcome for the inhaled human fungal pathogen Cryptococcus.

The majority of invasive human fungal pathogens gain access to their human hosts via the inhalation of spores from the environment into the lung, but relatively little is known about this infectious process. Among human fungal pathogens the most frequent cause of inhaled fatal fungal disease is Cryptococcus, which can disseminate from the lungs to other tissues, including the brain, where it causes meningoencephalitis. To determine the mechanisms by which distinct infectious particles of Cryptococcus cause disseminated disease, we evaluated two developmental cell types (spores and yeast) in mouse models of infection. We discovered that while both yeast and spores from several strains cause fatal disease, there was a consistently higher fungal burden in the brains of spore-infected mice. To determine the basis for this difference, we compared the pathogenesis of avirulent yeast strains with their spore progeny derived from sexual crosses. Strikingly, we discovered that spores produced by avirulent yeast caused uniformly fatal disease in the murine inhalation model of infection. We determined that this difference in outcome is associated with the preferential dissemination of spores to the lymph system. Specifically, mice infected with spores harbored Cryptococcus in their lung draining lymph nodes as early as one day after infection, whereas mice infected with yeast did not. Furthermore, phagocyte depletion experiments revealed this dissemination to the lymph nodes to be dependent on CD11c+ phagocytes, indicating a critical role for host immune cells in preferential spore trafficking. Taken together, these data support a model in which spores capitalize on phagocytosis by immune cells to escape the lung and gain access to other tissues, such as the central nervous system, to cause fatal disease. These previously unrealized insights into early interactions between pathogenic fungal spores and lung phagocytes provide new opportunities for understanding cryptococcosis and other spore-mediated fungal diseases.

Fungi subvert vaccine T cell priming at the respiratory mucosa by preventing chemokine-induced influx of inflammatory monocytes.

Vaccinologists strive to harness immunity at mucosal sites of pathogen entry. We studied respiratory delivery of an attenuated vaccine against Blastomyces dermatitidis. We created a T cell receptor transgenic mouse responsive to vaccine yeast and found that mucosal vaccination led to poor T cell activation in the draining nodes and differentiation in the lung. Mucosal vaccination subverted lung T cell priming by inducing matrix metalloproteinase 2 (MMP2), which impaired the action of the chemokine CCL7 on egress of CCR2(+) Ly6C(hi) inflammatory monocytes from the bone marrow and their recruitment to the lung. Studies in Mmp2(-/-) mice, or treatment with MMP inhibitor or rCCL7, restored recruitment of Ly6C(hi) monocytes to the lung and CD4(+) T cell priming. Mucosal vaccination against fungi and perhaps other respiratory pathogens may require manipulation of host MMPs in order to alter chemokine signals needed to recruit Ly6C(hi) monocytes and prime T cells at the respiratory mucosa.

An Analysis of Computed Tomography-Related Radiation Exposure in Pediatric Trauma Patients.

OBJECTIVE: To compare radiation doses used for pediatric computed tomography (CT) scans at community-based referring facilities (RF) to those at a designated pediatric trauma center (PTC) to assess the consistency of radiation exposure. METHODS: In this retrospective study, patients 0 to 18 years of age with CT imaging performed either at a RF or at a PTC from January 1, 2015, to January 5, 2016, were identified. Data about patients, CT radiation dose, and characteristics of the RFs were compared. RESULTS: We identified 502 patients (156 RF, 346 PTC) with 281 head CTs (79 RF, 202 PTC) and 86 abdominal/pelvis CTs (28 RF, 58 PTC). The radiation dose (measured in mean dose-length product [DLP] ± 1 standard deviation) was significantly higher for RF scans compared with PTC scans (head, RF DLP = 545 ± 334 vs PTC DLP = 438 ± 186 (P < 0.001); abdomen/pelvis, RF DLP = 279 ± 160 vs PTC DLP = 181 ± 201 [P = 0.027]). There was a nonsignificant trend toward lower head CT radiation dosages at RFs with a dedicated pediatric emergency department compared with RFs without a pediatric emergency department. CONCLUSIONS: Our data suggest that CT scans performed at RFs expose pediatric patients to significantly higher doses of radiation when compared with a PTC. These data support further study to identify factors associated with increased radiation and educational outreach to RFs.

Diagnostic Discordance in Pediatric Critical Care Transport: A Single-Center Experience.

OBJECTIVES: The aims of the study were to describe diagnostic discordance rates at our pediatric tertiary care center between the reason for transfer of critically ill/injured children (determined by the referring institution) and the inpatient admission diagnosis (determined by our accepting institution), to identify potential factors associated with discordance, and to determine its impact on patient outcomes. METHODS: We conducted a retrospective chart review of all critically ill/injured children transferred to the Johns Hopkins Children's Center between July 1, 2017, and June 30, 2018. All patients whose initial inpatient disposition was the pediatric intensive care unit were included. RESULTS: Six hundred forty-three children (median age, 51 months) from 57 institutions (median pediatric capability level: 3) met inclusion criteria: 46.8% were transported during nighttime, 86.5% by ground, and 21.2% accompanied by a physician. Nearly half (43.4%) had respiratory admission diagnoses. The rest included surgical/neurosurgical (14.2%), neurologic (11.2%), cardiovascular/shock (8.7%), endocrine (8.2%), infectious disease (6.8%), poisoning (3.1%), hematology-oncology (2.2%), gastrointestinal/metabolic (1.9%), and renal (0.3%). Forty-six (7.2%) had referral-to-admission diagnostic discordance: 25 of 46 had discordance across different diagnostic groups and 21 of 46 had clinically significant discordance within the same diagnostic group. The discordant group had higher need for respiratory support titration in transport (43.9% vs 27.9%, p = 0.02); more invasive procedures and vasopressor needs during the day of admission (26.1% vs 11.6%, P = 0.008; 19.6% vs 7%, P = 0.006); and longer intensive care unit (ICU) and hospital stays (5 vs 2 days; 11 vs 3 days, P < 0.001). When compared with respiratory admission diagnoses, patients with cardiovascular/shock and neurologic diagnoses were more likely to have discordant diagnoses (odds ratio [95% confidence interval], 13.24 [5.41-35.05]; 6.47 [2.48-17.75], P < 0.001). CONCLUSIONS: Seven percent of our critically ill/injured pediatric cohort had clinically significant referral-to-admission diagnostic discordance. Patients with cardiovascular/shock and neurologic diagnoses were particularly at risk. Those with discordant diagnoses had more in-transit events; a higher need for ICU interventions postadmission; and significantly longer ICU stays and hospitalizations, deserving further investigation.

An unappreciated role for neutrophil-DC hybrids in immunity to invasive fungal infections.

Neutrophils are classically defined as terminally differentiated, short-lived cells; however, neutrophils can be long-lived with phenotypic plasticity. During inflammation, a subset of neutrophils transdifferentiate into a population called neutrophil-DC hybrids (PMN-DCs) having properties of both neutrophils and dendritic cells. While these cells ubiquitously appear during inflammation, the role of PMN-DCs in disease remains poorly understood. We observed the differentiation of PMN-DCs in pre-clinical murine models of fungal infection: blastomycosis, aspergillosis and candidiasis. Using reporter strains of fungal viability, we found that PMN-DCs associate with fungal cells and kill them more efficiently than undifferentiated canonical neutrophils. During pulmonary blastomycosis, PMN-DCs comprised less than 1% of leukocytes yet contributed up to 15% of the fungal killing. PMN-DCs displayed higher expression of pattern recognition receptors, greater phagocytosis, and heightened production of reactive oxygen species compared to canonical neutrophils. PMN-DCs also displayed prominent NETosis. To further study PMN-DC function, we exploited a granulocyte/macrophage progenitor (GMP) cell line, generated PMN-DCs to over 90% purity, and used them for adoptive transfer and antigen presentation studies. Adoptively transferred PMN-DCs from the GMP line enhanced protection against systemic infection in vivo. PMN-DCs pulsed with antigen activated fungal calnexin-specific transgenic T cells in vitro and in vivo, promoting the production of interferon-γ and interleukin-17 in these CD4+ T cells. Through direct fungal killing and induction of adaptive immunity, PMN-DCs are potent effectors of antifungal immunity and thereby represent innovative cell therapeutic targets in treating life-threatening fungal infections.

CBLB Constrains Inactivated Vaccine-Induced CD8+ T Cell Responses and Immunity against Lethal Fungal Pneumonia.

Fungal infections in CD4+ T cell immunocompromised patients have risen sharply in recent years. Although vaccines offer a rational avenue to prevent infections, there are no licensed fungal vaccines available. Inactivated vaccines are safer but less efficacious and require adjuvants that may undesirably bias toward poor protective immune responses. We hypothesized that reducing the TCR signaling threshold could potentiate antifungal CD8+ T cell responses and immunity to inactivated vaccine in the absence of CD4+ T cells. In this study, we show that CBLB, a negative regulator of TCR signaling, suppresses CD8+ T cells in response to inactivated fungal vaccination in a mouse model of CD4+ T cell lymphopenia. Conversely, Cblb deficiency enhanced both the type 1 (e.g., IFN-γ) and type 17 (IL-17A) CD8+ T cell responses to inactivated fungal vaccines and augmented vaccine immunity to lethal fungal pneumonia. Furthermore, we show that immunization with live or inactivated vaccine yeast did not cause detectable pathologic condition in Cblb-/- mice. Augmented CD8+ T cell responses in the absence of CBLB also did not lead to terminal differentiation or adversely affect the expression of transcription factors T-bet, Eomes, and RORγt. Additionally, our adoptive transfer experiments showed that CBLB impedes the effector CD8+ T cell responses in a cell-intrinsic manner. Finally, we showed that ablation of Cblb overcomes the requirement of HIF-1α for expansion of CD8+ T cells upon vaccination. Thus, adjuvants that target CBLB may augment inactivated vaccines and immunity against systemic fungal infections in vulnerable patients.

LFA-1 Ligation by High-Density ICAM-1 Is Sufficient To Activate IFN-γ Release by Innate T Lymphocytes.

By binding to its ligand ICAM-1, LFA-1 is known to mediate both adhesion and costimulatory signaling for T cell activation. The constitutively high LFA-1 cell surface expression of invariant NKT (iNKT) cells has been shown to be responsible for their distinctive tissue homing and residency within ICAM-rich endothelial vessels. However, the functional impact of LFA-1 on the activation of iNKT cells and other innate T lymphocyte subsets has remained largely unexplored. In particular, it is not clear whether LFA-1 contributes to innate-like pathways of T cell activation, such as IFN-γ secretion in response to IL-12. Using a recombinant ICAM-1-Fc fusion protein to stimulate human iNKT cells in the absence of APCs, we show that LFA-1 engagement enhances their IL-12-driven IFN-γ production. Surprisingly, exposure to high densities of ICAM-1 was also sufficient to activate iNKT cell cytokine secretion independently of IL-12 and associated JAK/STAT signaling. LFA-1 engagement induced elevated cytoplasmic Ca2+ and rapid ERK phosphorylation in iNKT cells, and the resulting IFN-γ secretion was dependent on both of these pathways. Analysis of freshly isolated human PBMC samples revealed that a fraction of lymphocytes that showed elevated LFA-1 cell surface expression produced IFN-γ in response to plate-bound ICAM-1-Fc. A majority of the responding cells were T cells, with the remainder NK cells. The responding T cells included iNKT cells, MAIT cells, and Vδ2+ γδ T cells. These results delineate a novel integrin-mediated pathway of IFN-γ secretion that is a shared feature of innate lymphocytes.