Barriers and Facilitators to Participation in Health Screening: an Umbrella Review Across Conditions

Prevention Science - Screening is an essential prevention practice for a number of health conditions. However, screening coverage remains generally low. Studies that investigate determinants of...     

Comparative microbiological features of Bartonella henselae infection in a dog with fever of unknown origin and granulomatous lymphadenitis

We report the first documented case of Bartonella henselae infection in a dog from France and the first isolation of B. henselae from a dog with fever of unknown origin. This observation contributes to the “One Health” concept focusing on zoonotic pathogens emerging from companion animals. A 1-year-old female German shepherd dog was referred for evaluation of fever of unknown origin of 1 month duration. Diagnostic investigations confirmed diffuse pyogranulomatous lymphadenitis. The dog became afebrile, and lymph node size normalized in response to a 6-week course of doxycycline. Retrospectively, Bartonella DNA was amplified from an EDTA-anticoagulated blood sample obtained before antimicrobial therapy, with the gtlA fragment sharing 99 % identity with the 350-bp gtlA fragment of the B. henselae Houston-1 strain. The same strain was isolated in the blood of three healthy cats from the household. Two months after discontinuation of doxycycline, the dog experienced a febrile relapse. Bartonella DNA was again amplified from blood prior to and immediately after administration of a 6-week course azithromycin therapy. However, without administration of additional medications, PCR was negative 9 months after azithromycin therapy and the dog remains clinically healthy 12 months following the second course of antibiotics. The medical management of this case raises several clinically relevant comparative infectious disease issues, including the extent to which Bartonella spp. contribute to fever of unknown origin and pyogranulomatous inflammatory diseases in dogs and humans, and the potential of doxycycline and azithromycin treatment failures. The possibility that dogs could constitute an underestimated reservoir for B. henselae transmission to people is also discussed.     

What lessons can be learned from γδ T cell-based cancer immunotherapy trials?

During the last several years, research has produced a significant amount of knowledge concerning the characteristics of human γδ T lymphocytes. Findings regarding the immune functions of these cells, particularly their natural killer cell-like lytic activity against tumor cells, have raised expectations for the therapeutic applications of these cells for cancer. Pharmaceutical companies have produced selective agonists for these lymphocytes, and several teams have launched clinical trials of γδ T cell-based cancer therapies. The findings from these studies include hematological malignancies (follicular lymphoma, multiple myeloma, acute and chronic myeloid leukemia), as well as solid tumors (renal cell, breast and prostate carcinomas), consisting of samples from more than 250 patients from Europe, Japan and the United States. The results of these pioneering studies are now available, and this short review summarizes the lessons learned and the role of γδ T cell-based strategies in the current landscape of cancer immunotherapies.     

Dissecting the interface between apicomplexan parasite and host cell: Insights from a divergent AMA–RON2 pair

Plasmodium falciparum and Toxoplasma gondii are widely studied parasites in phylum Apicomplexa and the etiological agents of severe human malaria and toxoplasmosis, respectively. These intracellular pathogens have evolved a sophisticated invasion strategy that relies on delivery of proteins into the host cell, where parasite-derived rhoptry neck protein 2 (RON2) family members localize to the host outer membrane and serve as ligands for apical membrane antigen (AMA) family surface proteins displayed on the parasite. Recently, we showed that T. gondii harbors a novel AMA designated as TgAMA4 that shows extreme sequence divergence from all characterized AMA family members. Here we show that sporozoite-expressed TgAMA4 clusters in a distinct phylogenetic clade with Plasmodium merozoite apical erythrocyte-binding ligand (MAEBL) proteins and forms a high-affinity, functional complex with its coevolved partner, TgRON2_L1. High-resolution crystal structures of TgAMA4 in the apo and TgRON2_L1-bound forms complemented with alanine scanning mutagenesis data reveal an unexpected architecture and assembly mechanism relative to previously characterized AMA–RON2 complexes. Principally, TgAMA4 lacks both a deep surface groove and a key surface loop that have been established to govern RON2 ligand binding selectivity in other AMAs. Our study reveals a previously underappreciated level of molecular diversity at the parasite–host-cell interface and offers intriguing insight into the adaptation strategies underlying sporozoite invasion. Moreover, our data offer the potential for improved design of neutralizing therapeutics targeting a broad range of AMA–RON2 pairs and apicomplexan invasive stages.Phylum Apicomplexa comprises >5,000 parasitic protozoan species, many of which cause devastating diseases on a global scale. Two of the most prevalent species are Toxoplasma gondii and Plasmodium falciparum, the causative agents of toxoplasmosis and severe human malaria, respectively (1, 2). The obligate intracellular apicomplexan parasites lead complex and diverse lifestyles that require invasion of many different cell types. Despite this diversity of target host cells, most apicomplexans maintain a generally conserved mechanism for active invasion (3). The parasite initially glides over the surface of a host cell and then reorients to place its apical end in close contact to the host-cell membrane. After this initial attachment, a circumferential ring of adhesion (termed the moving or tight junction) is formed, through which the parasite actively propels itself while concurrently depressing the host-cell membrane to create a nascent protective vacuole (4).Formation of the moving junction relies on a pair of highly conserved parasite proteins: rhoptry neck protein 2 (RON2) and apical membrane antigen 1 (AMA1). Initially, parasites discharge RON2 into the host cell membrane where an extracellular portion (domain 3; D3) serves as a ligand for AMA1 displayed on the parasite surface (5–8). Intriguingly, recent studies have shown that the AMA1–RON2 complex is an attractive target for therapeutic intervention (9–12). The importance of the AMA1–RON2 pairing is also reflected in the observation that many apicomplexan parasites encode functional paralogs that are generally expressed in a stage-specific manner (13–15). We recently showed that, in addition to AMA1 and RON2, T. gondii harbors three additional AMA paralogs and two additional RON2 paralogs (14, 15): TgAMA2 forms a functional invasion complex with TgRON2 (15), TgAMA3 (also annotated as SporoAMA1) selectively coordinates TgRON2_L2 (14), and TgAMA4 binds TgRON2_L1 (15). Despite substantial sequence divergence, structural characterization of all AMA–RON2D3 complexes solved to date [TgAMA1–TgRON2D3 (16), PfAMA1–PfRON2D3 (17), and TgAMA3–TgRON2_L2D3 (14)] reveal a largely conserved architecture and binding paradigm. Intriguingly, however, sequence analysis indicates that TgAMA4 and TgRON2_L1 are likely to adopt substantially divergent structures with an atypical assembly mechanism.To investigate the functional implications of the AMA4–RON2_L1 complex in T. gondii, we first established that TgAMA4 is part of a highly divergent AMA clade that includes the functionally important malaria vaccine candidate Plasmodium merozoite apical erythrocyte-binding ligand (MAEBL) (18–20) and that TgRON2_L1 displays a similar divergence consistent with coevolution of receptor and ligand. We then show that TgAMA4 and TgRON2_L1 form a high-affinity binary complex and probe its overall architecture and underlying mechanism of assembly using crystal structures of TgAMA4 in the apo and TgRON2_L1D3 bound forms. Finally, we show proof of principle that TgAMA4 and TgRON2_L1 form a functional pairing capable of supporting host-cell invasion. Collectively, our study reveals exceptional molecular diversity at the parasite–host-cell interface that we discuss in the context of the unique invasion barriers encountered by the sporozoite.