Ei-patogeenisten ja patogeenisten bakteerien aiheuttama luontaisen immuniteetin aktivoituminen ihmisen leukosyyteissä

The human body is continuously interacting with microbes. Cells of the immune system protect the host from microbes some of which can occasionally cause diseases. Macrophages and dendritic cells (DC) play a central role in innate and adaptive immune responses and they are activated in response to microbial stimulation. During activation these cells produce cytokines, soluble mediators that regulate host immune responses. Recognition of microbes is regulated by multiple host cell receptor systems which activate intracellular signalling pathways ultimately leading to the expression of genes involved in innate and adaptive immune responses. In this thesis the interactions between human leukocytes and various bacteria were studied using human macrophages and DCs. The innate immune responses induced by probiotic and other non-pathogenic bacteria in macrophages and DCs were compared with the responses induced by a pathogenic bacterium Streptococcus pyogenes. The differences in the gene expression profiles of cytokine and chemokine genes and the activation of different signalling pathways were analysed. Although both cell types effectively destroy invading microbes the cytokine patterns they produced in response to bacterial stimulation varied significantly. Macrophages responded to bacterial stimulation in a nearly similar fashion whether the bacteria had probiotic, non-pathogenic, or pathogenic characteristics. Interestingly, DCs showed a much wider variability in their responses to different bacteria. Some non-pathogenic bacteria did not induce detectable levels of cytokines in DCs while others were even more efficient than S. pyogenes in inducing cytokine responses. DC maturation marker molecules were induced in response to non-pathogenic bacteria with relatively weak cytokine production patterns. This led to a semi-mature DC phenotype, which could be involved in tolerogenic responses seen in host cell interactions with commensal bacteria. The other focus of this work was to evaluate the role of dynamin-dependent endocytosis and streptococcal virulence factors, streptolysins, in the immune responses induced by S. pyogenes in macrophages. Streptolysins were not critical for the inflammatory responses induced by this bacterium, suggesting a cooperation of various virulence factors in bacterial pathogenesis. This work provides better understanding of the functions of the innate immune system upon contact with non-pathogenic and pathogenic bacteria. The results may provide useful information for the interpretation of the results obtained from probiotic clinical trials and help to select new candidate probiotic strains for clinical use. In addition, this work identifies new details on the mechanisms of S. pyogenes -induced inflammatory responses.Elimistön solut sekä ympäristön bakteerit ovat jatkuvasti vuorovaikutuksessa toistensa kanssa. Osa mikrobeista on harmittomia, jopa hyödyllisiä, toiset puolestaan voivat aiheuttaa tauteja päästessään elimistöön. Luontainen immuniteetti pyrkii tuhoamaan elimistölle vaaralliset mikrobit nopeasti syöjäsolujen kuten makrofagien ja antigeeneja esittelevien dendriittisolujen toimesta. Nämä solut tunnistavat bakteereita erilaisten reseptoreiden välityksellä ja tuottavat sytokiineja, jotka toimivat välittäjämolekyyleinä ohjaten immuunivasteiden kehittymistä. Tässä työssä on tutkittu ihmisen leukosyyttien ja bakteerien välisiä vuorovaikutussuhteita käyttäen mallina ihmisen veren monosyyteistä erilaistettuja dendriittisoluja ja makrofageja. Työssä on havaittu eroja probioottien, potentiaalisten probioottien ja patogeenisen Streptococcus pyogenes -bakteerin kyvyssä aktivoida immuunivasteita. Bakteereilla stimuloitujen dendriittisolujen aktivaatiota ja sytokiinituotantoa verrattiin makrofageissa syntyviin vasteisiin. Ei-patogeeniset bakteerit saivat aikaan dendriittisolujen kypsymisen ja kostimulatoristen molekyylien ilmentymisen solujen pinnalla, mutta niiden kyky aktivoida sytokiinituotanto vaihteli huomattavasti. Osa bakteereista ei aktivoinut sytokiinituotantoa lainkaan, toiset puolestaan aktivoivat sen voimakkaammin kuin patogeeninen S. pyogenes -bakteeri. Jotkut bakteereista saivat aikaan dendriittisolujen osittaisen kypsymisen. Tällaiset solut ilmentävät kostimulatorisia molekyylejä, mutta eivät tuota sytokiineja, ja niiden uskotaan osallistuvan tolerogeenisten vasteiden syntymiseen. Tämä saattaa selittää elimistön ja normaalin mikrobiston välistä toleranssia. Makrofageissa kaikki tutkitut bakteerit saivat aikaan voimakkaan tai suhteellisen voimakkaan inflammatorisen vasteen. Tutkimuksessa selvitettiin myös dynamiinivälitteisen endosytoosin osuutta puolustusvasteen synnyssä sekä verrattiin villityyppisen S. pyogenes bakteerin ja streptolysiinivirulenssitekijöiden osalta puutteellisten bakteerien kykyä aktivoida makrofageja. Tutkimuksessa havaittiin, että streptolysiinit eivät ole välttämättömiä S. pyogenes -bakteerin aikaansaamien inflammatoristen vasteiden synnyssä. Työstä saatu tieto auttaa ymmärtämään luontaisen immuunijärjestelmän toimintaa elimistön kohdatessa erilaisia bakteereita. Saatua tietoa voidaan hyödyntää tutkittaessa probioottisten bakteerien aikaansaamia terveysvaikutuksia ja niiden taustalla olevia mekanismeja. Lisäksi tutkimus selventää S. pyogenes -infektioiden immunologisia mekanismeja, joita voidaan hyödyntää kehitettäessä menetelmiä hallita bakteerin aiheuttamia voimakkaita immuunivasteita

RIG-I signaling Is essential for influenza B virus-induced rapid interferon gene expression

Influenza B virus causes annual epidemics and, along with influenza A virus, accounts for substantial disease and economic burden throughout the world. Influenza B virus infects only humans and some marine mammals and is not responsible for pandemics, possibly due to a very low frequency of reassortment and a lower evolutionary rate than that of influenza A virus. Influenza B virus has been less studied than influenza A virus, and thus, a comparison of influenza A and B virus infection mechanisms may provide new insight into virus-host interactions. Here we analyzed the early events in influenza B virus infection and interferon (IFN) gene expression in human monocyte-derived macrophages and dendritic cells. We show that influenza B virus induces IFN regulatory factor 3 (IRF3) activation and IFN-λ1 gene expression with faster kinetics than does influenza A virus, without a requirement for viral protein synthesis or replication. Influenza B virus-induced activation of IRF3 required the fusion of viral and endosomal membranes, and nuclear accumulation of IRF3 and viral NP occurred concurrently. In comparison, immediate early IRF3 activation was not observed in influenza A virus-infected macrophages. Experiments with RIG-I-, MDA5-, and RIG-I/MDA5-deficient mouse fibroblasts showed that RIG-I is the critical pattern recognition receptor needed for the influenza B virus-induced activation of IRF3. Our results show that innate immune mechanisms are activated immediately after influenza B virus entry through the endocytic pathway, whereas influenza A virus avoids early IRF3 activation and IFN gene induction. IMPORTANCE Recently, a great deal of interest has been paid to identifying the ligands for RIG-I under conditions of natural infection, as many previous studies have been based on transfection of cells with different types of viral or synthetic RNA structures. We shed light on this question by analyzing the earliest step in innate immune recognition of influenza B virus by human macrophages. We show that influenza B virus induces IRF3 activation, leading to IFN gene expression after viral RNPs (vRNPs) are released into the cytosol and are recognized by RIG-I receptor, meaning that the incoming influenza B virus is already able to activate IFN gene expression. In contrast, influenza A (H3N2) virus failed to activate IRF3 at very early times of infection, suggesting that there are differences in innate immune recognition between influenza A and B viruses

Role of Probiotics in Stimulating the Immune System in Viral Respiratory Tract Infections: A Narrative Review

Viral respiratory tract infection (RTI) is the most frequent cause of infectious illnesses including the common cold. Pharmacological solutions for treating or preventing viral RTIs are so far limited and thus several self-care products are available in the market. Some dietary supplements such as probiotics have been shown to modulate immune system function and their role in reducing the risk and the course of RTIs has been investigated extensively within the past decade. However, the mechanism of action and the efficacy of probiotics against viral RTIs remains unclear. We searched PubMed, Google Scholar, and Web of Knowledge for pre-clinical and clinical studies investigating the effect of probiotics on respiratory virus infections, immune response, and the course of upper and lower respiratory tract illness. The literature summarized in this narrative review points out that specific probiotic strains seem effective in pre-clinical models, through stimulating the immune system and inhibiting viral replication. Clinical studies indicate variable efficacy on upper respiratory illnesses and lack proof of diagnosed viral infections. However, meta-analyses of clinical studies indicate that probiotics could be beneficial in upper respiratory illnesses without specific etiology. Further studies aiming at discovering the mechanisms of action of probiotics and clinical efficacy are warranted

Live Lactobacillus rhamnosus and Streptococcus pyogenes differentially regulate Toll-like

receptor (TLR) gene expression in human primary macrophage

Potentially probiotic bacteria induce efficient maturation but differential cytokine production in human monocyte-derived dendritic cells

AIM: To analyze the ability of nine different potentially probiotic bacteria to induce maturation and cytokine production in human monocyte-derived dendritic cells (moDCs)