Human inherited CCR2 deficiency underlies progressive polycystic lung disease.

We describe a human lung disease caused by autosomal recessive, complete deficiency of the monocyte chemokine receptor C-C motif chemokine receptor 2 (CCR2). Nine children from five independent kindreds have pulmonary alveolar proteinosis (PAP), progressive polycystic lung disease, and recurrent infections, including bacillus Calmette Guérin (BCG) disease. The CCR2 variants are homozygous in six patients and compound heterozygous in three, and all are loss-of-expression and loss-of-function. They abolish CCR2-agonist chemokine C-C motif ligand 2 (CCL-2)-stimulated Ca2+ signaling in and migration of monocytic cells. All patients have high blood CCL-2 levels, providing a diagnostic test for screening children with unexplained lung or mycobacterial disease. Blood myeloid and lymphoid subsets and interferon (IFN)-γ- and granulocyte-macrophage colony-stimulating factor (GM-CSF)-mediated immunity are unaffected. CCR2-deficient monocytes and alveolar macrophage-like cells have normal gene expression profiles and functions. By contrast, alveolar macrophage counts are about half. Human complete CCR2 deficiency is a genetic etiology of PAP, polycystic lung disease, and recurrent infections caused by impaired CCL2-dependent monocyte migration to the lungs and infected tissues.

Cross-presenting Langerhans cells are required for the early reactivation of resident CD8+ memory T cells in the epidermis.

Tissue-resident memory CD8+ T cells (TRM) reside at sites of previous infection, providing protection against reinfection with the same pathogen. In the skin, TRM patrol the epidermis, where keratinocytes are the entry site for many viral infections. Epidermal TRM react rapidly to cognate antigen encounter with the secretion of cytokines and differentiation into cytotoxic effector cells, constituting a first line of defense against skin reinfection. Despite the important protective role of skin TRM, it has remained unclear, whether their reactivation requires a professional antigen-presenting cell (APC). We show here, using a model system that allows antigen targeting selectively to keratinocytes in a defined area of the skin, that limited antigen expression by keratinocytes results in rapid, antigen-specific reactivation of skin TRM. Our data identify epidermal Langerhans cells that cross-present keratinocyte-derived antigens, as the professional APC indispensable for the early reactivation of TRM in the epidermal layer of the skin.

Effects of Low-Level Persistent Infection on Maintenance of Immunity by CD4 T Cell Subsets and Th1 Cytokines.

CD4 T cells are required, along with antibodies, for complete protection from blood-stage infection with Plasmodium spp., which cause malaria. Without continuous exposure, as on emigration of people from endemic areas, protection from malaria decays. As in other persistent infections, low-level Plasmodium chabaudi infection protects the host from reinfection at 2 months postinfection, a phenomenon termed premunition. Premunition is correlated with T cell responses, rather than antibody levels. We previously showed that while both effector T cells (Teff) and memory T cells (Tmem) are present after infection, Teff protect better than Tmem. Here, we studied T cell kinetics post-infection by labeling dividing Ifng+ T cells with 5-bromo-2'-deoxyuridine (BrdU) in infected Ifng reporter mice. Large drops in specific T cell numbers and Ifng+ cells upon clearance of parasites suggest a mechanism for decay of protection. Although protection decays, CD4 Tmem persist, including a highly differentiated CD27- effector memory (Tem) subset that maintains some Ifng expression. In addition, pretreatment of chronically infected animals with neutralizing antibody to interferon gamma (IFN-γ) or with clodronate liposomes before reinfection decreases premunition, supporting a role for Th1-type immunity to reinfection. A pulse-chase experiment comparing chronically infected to treated animals showed that recently divided Ifng+ T cells, particularly IFN-γ+ TNF+ IL-2- T cells, are promoted by persistent infection. These data suggest that low-level persistent infection reduces CD4+ Tmem and multifunctional Teff survival, but promotes IFN-γ+ TNF+ IL-2- T cells and Ifng+ terminally differentiated effector T cells, and prolongs immunity.

Recurrent infections drive persistent bladder dysfunction and pain via sensory nerve sprouting and mast cell activity.

Urinary tract infections (UTIs) account for almost 25% of infections in women. Many are recurrent (rUTI), with patients frequently experiencing chronic pelvic pain and urinary frequency despite clearance of bacteriuria after antibiotics. To elucidate the basis for these bacteria-independent bladder symptoms, we examined the bladders of patients with rUTI. We noticed a notable increase in neuropeptide content in the lamina propria and indications of enhanced nociceptive activity. In mice subjected to rUTI, we observed sensory nerve sprouting that was associated with nerve growth factor (NGF) produced by recruited monocytes and tissue-resident mast cells. Treatment of rUTI mice with an NGF-neutralizing antibody prevented sprouting and alleviated pelvic sensitivity, whereas instillation of native NGF into naïve mice bladders mimicked nerve sprouting and pain behavior. Nerve activation, pain, and urinary frequency were each linked to the presence of proximal mast cells, because mast cell deficiency or treatment with antagonists against receptors of several direct or indirect mast cell products was each effective therapeutically. Thus, our findings suggest that NGF-driven sensory sprouting in the bladder coupled with chronic mast cell activation represents an underlying mechanism driving bacteria-independent pain and voiding defects experienced by patients with rUTI.

Brucella Egresses from Host Cells Exploiting Multivesicular Bodies.

Host cell egress is a critical step in the life cycle of intracellular pathogens, especially in microbes capable of establishing chronic infections. The Gram-negative bacterium Brucella belongs to such a group of pathogens. Even though much has been done to understand how Brucella avoids killing and multiplies in its intracellular niche, the mechanism that this bacterium deploys to egress from the cell to complete its cycle has been poorly studied. In the manuscript, we quantify the kinetics of bacterial egress and show that Brucella exploits multivesicular bodies to exit host cells. For the first time, we visualized the process of egress in real time by live video microscopy and showed that a population of intracellular bacteria exit from host cells in vacuoles containing multivesicular body-like features. We observed the colocalization of Brucella with two multivesicular markers, namely, CD63 and LBPA, both during the final stages of the intracellular life cycle and in egressed bacteria. Moreover, drugs that either promote or inhibit multivesicular bodies either increased or decreased the number of extracellular bacteria, respectively. Our results strongly suggest that Brucella hijacks multivesicular bodies to exit the host cells to initiate new infection events. IMPORTANCE How intracellular bacterial pathogens egress from host cells has been poorly studied. This is particularly important because this stage of the infectious cycle can have a strong impact on how the host resolves the infection. Brucella is an intracellular pathogen that infects mammals, including humans, and causes a chronic debilitating illness. The bacterium has evolved a plethora of mechanisms to invade host cells, avoid degradation in the endocytic pathway, and actively multiply within a specialized intracellular compartment. However, how this pathogen exits from infected cells to produce reinfection and complete its life cycle is poorly understood. In the manuscript, we shed some light on the mechanisms that are exploited by Brucella to egress from host cells. We observed for the first time the egress of Brucella from infected cells by time-lapse video microscopy, and we found that the bacterium exits in vesicles containing multivesicular bodies (MVBs) features. Moreover, the drug manipulation of MVBs resulted in the alteration of bacterial egress efficiency. Our results indicate that Brucella hijacks MVBs to exit host cells and that this strongly contributes to the reinfection cycle.

Symptomatic SARS-CoV-2 Reinfection in a Healthy Healthcare Worker in Italy Confirmed by Whole-Genome Sequencing.

This study describes a case of SARS-CoV-2 reinfection confirmed by whole-genome sequencing in a healthy physician who had been working in a COVID-19 hospital in Italy since the beginning of the pandemic. Nasopharyngeal swabs were obtained from the patient at each presentation as part of routine surveillance. Nucleic acid amplification testing was performed on the two samples to confirm SARS-CoV-2 infection, and serological tests were used to detect SARS-CoV-2 IgG antibodies. Comparative genome analysis with whole-genome sequencing was performed on nasopharyngeal swabs collected during the two episodes of COVID-19. The first COVID-19 episode was in March 2020, and the second was in January 2021. Both SARS-CoV-2 infections presented with mild symptoms, and seroconversion for SARS-CoV-2 IgG was documented. Genomic analysis showed that the viral genome from the first infection belonged to the lineage B.1.1.74, while that from the second infection to the lineage B.1.177. Epidemiological, clinical, serological, and genomic analyses confirmed that the second episode of SARS-CoV-2 infection in the healthcare worker met the qualifications for "best evidence" for reinfection. Further studies are urgently needed to assess the frequency of such a worrisome occurrence, particularly in the light of the recent diffusion of SARS-CoV-2 variants of concern.

Prophylaxis of Hepatitis B Virus (HBV) Re-Infection in Liver Transplantation: Is the Reappearance of Hepatitis B Surface Antigen (HBsAg) Significant?

The recurrence of hepatitis B virus (HBV) infection after orthotopic liver transplantation (OLT) was in the past a primary cause of organ loss or mortality. Currently, post-OLT prophylaxis with anti-HBs immunoglobulins plus a nucleos(t)ide analogue has virtually abolished the risk of re-infection. Some studies have proposed to simplify prophylaxis by discontinuing immunoglobulins while continuing the analogue alone. This review analysed the available studies, focusing on the recurrence of HBsAg in serum and its biological effects. In all, 16 studies were retrieved, mainly observational or retrospective, each enrolling 14 to 80 patients. Our review of the literature found that HBsAg re-appeared in 0% to 24% of the patients, generally with HBV DNA undetectable in plasma. One study measured HBsAg using a new ultra-sensitive method, which could allow a reappraisal of the incidence of recurrence. This review discusses the role of HBV surface proteins in inducing hepatocellular carcinoma, particularly when mutations in the C-terminal occur that induce stop-codons that cause defects of secretion and retention of truncated protein S, resulting in direct cell toxicity and cancer. The data on the suspension of immunoglobulins in the prophylaxis regimes of post-transplant re infection do not appear sufficiently robust for an extensive and safe application in clinical practice.