Virulenssitekijöiden vaikutus Streptococcus pneumoniae -bakteerin kykyyn suojautua komplementilta

Streptococcus pneumoniae (pneumococcus) is a normal inhabitant of the human nasopharynx. Symptoms occur in only a small proportion of those who become carriers, but the ubiquity of the organism in the human population results in a large burden of disease. S. pneumoniae is the leading bacterial cause of pneumonia, sepsis, and meningitis worldwide, causing the death of a million children each year. Middle-ear infection is the most common clinical manifestation of mucosal pneumococcal infections. In invasive disease, S. pneumoniae gains access to the bloodstream and spreads to normally sterile parts of the body. The progression from asymptomatic colonization to disease depends on factors characteristic of specific pneumococcal strains as well as the status of host defenses. The polysaccharide capsule surrounding the bacterium is considered to be the most important factor affecting the virulence of pneumococci. It protects pneumococci from phagocytosis and also may determine its affinity to the respiratory epithelium. S. pneumoniae as a species comprises more than 90 different capsular serotypes, but not all of them are equally prevalent in human diseases. Invasive serotypes are rarely isolated from healthy carriers, but relatively often cause invasive disease. Serotypes that are carried asymptomatically for a long time behave like opportunistic pathogens, causing disease in patients who have impaired immune defenses. The complement system is a collection of blood and cell surface proteins that act as a major primary defense against invading microbes. Phagocytic cells with receptors for complement proteins can engulf and destroy pneumococcal cells opsonized with these proteins. S. pneumoniae has evolved a number of ways to subvert mechanisms of innate immunity, and this is likely to contribute to its pathogenicity. The capsular serotype, proteins essential for virulence, as well the genotype, may all influence the ability of pneumococcus to resist complement and its potential to cause disease. Immunization with conjugate vaccines produces opsonic antibodies, which enhance complement deposition and clearance of the bacteria. The pneumococcal vaccine included in the Finnish national immunization program in 2010 contains the most common serotypes causing invasive disease. Clinical data suggest that protection from middle-ear infection and possibly also from invasive disease depends largely on the capsular serotype, for reasons hitherto unknown. The general aim of this thesis is to assess the relative roles of the pneumococcal capsule and virulence proteins in complement evasion and subsequent opsonophagocytic killing. The main question is whether differences between serotypes to resist complement explain the different abilities of serotypes to cause disease. The importance of particular virulence factors to the complement resistance of a strain may vary depending on its genotype. Prior studies have evaluated the effect of the capsule and virulence proteins on complement resistance of S. pneumoniae by comparing only a few strains. In this thesis, the role of pneumococcal virulence factors in the complement resistance of the bacterium was studied in several genotypically different strains. The ability of pneumococci to inhibit deposition of the complement protein C3 on the bacterial surface was found to depend on the capsular serotype as well as on other features of the bacteria. The results suggest that pneumococcal histidine triad (Pht) proteins may play a role in complement inhibition, but their contribution depends on the bacterial genotype. The capsular serotype was found to influence complement resistance more than the bacterial genotype. A higher concentration of anticapsular antibodies was required for the opsonophagocytic killing of serotypes resistant to C3 deposition. The invasive serotypes were more resistant to C3 deposition than the opportunistic serotypes, suggesting that the former are better adapted to resist immune mechanisms controlling the development of invasive disease. The different susceptibilities of serotypes to complement deposition, opsonophagocytosis, and resultant antibody-mediated protection should be taken into account when guidelines for serological correlates for vaccine efficacy evaluations are made. The results of this thesis suggest that antibodies in higher quantity or quality are needed for efficient protection against the invasive serotypes.Pneumokokki suojautuu elimistön puolustuskeinoilta kapselinsa avulla Streptococcus pneumoniae (pneumokokki) on bakteeri, jonka luonnollinen elinympäristö on ihmisen nenänielu. Sopivissa olosuhteissa pneumokokki voi aiheuttaa korvatulehdusta ja keuhkokuumetta sekä vakavia tauteja, joissa bakteeri tunkeutuu verenkiertoon. Pneumokokin taudinaiheuttamiskyvylle tärkein tekijä on bakteeria ympäröivä kapseli, josta tunnetaan yli 90 erilaista muotoa. Vain pieni osa kapselityypeistä aiheuttaa valtaosan vakavista pneumokokkitaudeista. Rokottamalla elimistö saadaan tuottamaan vasta-aineita rokotteen sisältämiä kapselityyppejä vastaan, millä kyetään ehkäisemään pneumokokin aiheuttamia tauteja. FM Merit Melin havaitsi väitöskirjatyössään pneumokokin kapselityypin vaikuttavan merkittävästi bakteerin kykyyn vastustaa elimistön puolustuskeinoja. Pneumokokkien herkkyyttä immuunipuolustukselle selvitettiin laboratoriokokein mittaamalla komplementin sitoutumista bakteerien pinnalle ja valkosolujen välittämää bakteerien tappoa. Komplementti koostuu joukosta veressä ja solujen pinnoilla esiintyviä proteiineja. Sillä on keskeinen merkitys elimistön puolustuksessa taudinaiheuttajia vastaan. Valkosolut, jotka ilmentävät pinnallaan erityisiä reseptoreja, tunnistavat ja nielaisevat komplementtiproteiineilla päällystetyt pneumokokkisolut estäen näin bakteerin leviämisen elimistössä. Pneumokokin taudinaiheuttamiskyvyn kannalta on ratkaisevaa, että se kykenee suojautumaan synnynnäiseltä immuunipuolustukselta. Taudinaiheuttajan kohtaamisen tai rokottamisen seurauksena muodostuvat vasta-aineet tehostavat komplementin kertymistä bakteerin pinnalle ja siten edesauttavat solusyöntiä. Melinin väitöskirjatyössä vakavia tauteja aiheuttavat kapselityypit osoittautuivat olevan vastustuskykyisempiä komplementille, mikä merkitsee, että niiltä suojautumiseksi tarvitaan runsaammin vasta-aineita kuin nenänielussa useimmiten oireettomana esiintyviä pneumokokkeja vastaan. Havainto tukee kansainvälisiä tutkimuksia, joiden perusteella rokotteen suoja välikorvatulehdusta ja mahdollisesti myös vakavia tautimuotoja vastaan vaihtelee kapselin tyypistä riippuen. Kansalliseen rokotusohjelmaan 2010 sisällytetty pneumokokkirokote suojaa hyvin Suomessa lapsilla yleisimmin vakavia tauteja aiheuttavilta pneumokokeilta. Tiettyjä kehitysmaissa tärkeitä kapselityyppejä vastaan suoja ei ole täydellinen. Vastustuskykyisiltä pneumokokeilta suojautumiseksi tehokkaan rokotteen tulisi tuottaa korkeampi vasta-aineiden pitoisuus tai laadullisesti tehokkaampia vasta-aineita. Tutkimus tuo uutta tietoa pneumokokin taudinaiheuttamiskyvylle tärkeistä ominaisuuksista ja keinoista, joilla bakteeri suojautuu ihmisen immuunipuolustukselta. Tietoa voidaan hyödyntää nykyisten ja uusien pneumokokkirokotteiden kehitystyössä

Koronarokotteiden neljännet annokset; kenelle ja miksi?

Taustatietoa Kansallisen rokotusasiantuntijaryhmän sekä Terveyden ja hyvinvoinnin laitoksen päätöksentekoa varten

Koronarokotukset syystalvella 2023 : suositus ja näyttöpohja

THL antoi toukokuussa 2023 ennakkoarvion koronarokotusten tehosteannoskierroksesta syystalvelle 2023 toteutettavaksi influenssarokotusten yhteydessä. Toukokuussa ei vielä ollut tiedossa syksyllä käytettävissä olevien uusien rokotevalmisteiden koostumus eikä Suomeen saatavien rokotteiden määrä. Sen vuoksi THL antoi ennakkoarvion, jota luvattiin tarkentaa elokuussa. Vuosi sitten THL antoi syystalven tehosteannossuosituksen kaikille 65 vuotta täyttäneille, 18 vuotta täyttäneille riskiryhmiin kuuluville sekä 12 vuotta täyttäneille voimakkaasti immuunipuutteisille. Olennaista oli, että rokotettava sai yhden varianttiräätälöidyn tehosteannoksen, kun oli kulunut vähintään 3 kuukautta edellisestä rokoteannoksesta tai sairastetusta koronataudista. Tällä yhdellä tehosteannoksella saatiin riskiryhmiin kuuluville lisäsuojaa vakavaa tautia vastaan talvikaudelle, jolloin hengitystieinfektioiden ilmaantuvuus yleensä kasvaa. Tehosteannos suositeltiin annettavaksi influenssarokotusten yhteydessä. Syystalvelle 2023 annetaan samanlainen suositus, mutta rokotteena käytetään XBB.1.5-räätälöityä rokotetta. THL on seurannut jatkuvasti koronan epidemiatilannetta, rokotusten suojatehoa ja turvallisuutta, sairaalahoidon ilmaantuvuutta sekä kertynyttä tutkimustietoa. THL julkaisi maaliskuussa 2023 kattavan työpaperin koronarokotuksista numeroinnilla 11/2023. Nykyhetkeen verrattuna muuttumattomina pysyneet asiat on jätetty pois tästä työpaperista. Tämä työpaperi esittelee tilannetta touko-elokuussa 2023. Työpaperi sisältää toukokuun ennakkoarvion sekä kesän aikana tehdyt tarkennukset syystalven 2023 koronarokotuksista

A Highly Sensitive and Specific SARS-CoV-2 Spike- and Nucleoprotein-Based Fluorescent Multiplex Immunoassay (FMIA) to Measure IgG, IgA, and IgM Class Antibodies

Validation and standardization of accurate serological assays are crucial for the surveillance of the coronavirus disease 2019 (COVID-19) pandemic and population immunity. We describe the analytical and clinical performance of an in-house fluorescent multiplex immunoassay (FMIA) for simultaneous quantification of antibodies against the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) nucleoprotein and spike glycoprotein. Furthermore, we calibrated IgG-FMIA against World Health Organization (WHO) International Standard and compared FMIA results to an in-house enzyme immunoassay (EIA) and a microneutralization test (MNT). We also compared the MNT results of two laboratories. IgG-FMIA displayed 100% specificity and sensitivity for samples collected 13 to 150 days post-onset of symptoms (DPO). For IgA- and IgM-FMIA, 100% specificity and sensitivity were obtained for a shorter time window (13 to 36 and 13 to 28 DPO for IgA- and IgM-FMIA, respectively). FMIA and EIA results displayed moderate to strong correlation, but FMIA was overall more specific and sensitive. IgG-FMIA identified 100% of samples with neutralizing antibodies (NAbs). Anti-spike IgG concentrations correlated strongly (r = 0.77 to 0.84, P < 2.2 x 10(-16)) with NAb titers, and the two laboratories' NAb titers displayed a very strong correlation (r = 0.95, P< 2.2 x 10(-16)). Our results indicate good correlation and concordance of antibody concentrations measured with different types of in-house SARS-CoV-2 antibody assays. Calibration against the WHO international standard did not, however, improve the comparability of FMIA and EIA results. IMPORTANCE SARS-CoV-2 serological assays with excellent clinical performance are essential for reliable estimation of the persistence of immunity after infection or vaccination. In this paper we present a thoroughly validated SARS-CoV-2 serological assay with excellent clinical performance and good comparability to neutralizing antibody titers. Neutralization tests are still considered the gold standard for SARS-CoV-2 serological assays, but our assay can identify samples with neutralizing antibodies with 100% sensitivity and 96% specificity without the need for laborious and slow biosafety level 3 (BSL-3) facility-requiring analyses.Peer reviewe

Similar Antibody Levels in 3-Year-Old Children Vaccinated Against Measles, Mumps, and Rubella at the Age of 12 Months or 18 Months

Background. Measles-mumps-rubella (MMR) vaccinations have been offered to Finnish children at 14-18 months and 6 years of age. In May 2011, the recommended age for the first vaccine dose was lowered to 12 months because of the European measles epidemic. Methods. Fingertip capillary blood samples were collected from 3-year-old Finnish children vaccinated once with MMR vaccine at 11-19 months of age. The immunoglobulin G (IgG) antibodies to all 3 MMR antigens were measured with enzyme-linked immunosorbent assay. Neutralizing antibodies and the avidity of antibodies were measured for measles virus. Results. From April through October 2013, 187 children were enrolled. Equally high proportions of the samples were seropositive for measles virus, mumps virus, or rubella virus antibodies, and there were no significant differences in the IgG antibody concentrations in children vaccinated at 11-13 months of age, compared with those vaccinated at 17-19 months of age. However, among children vaccinated at 11-13 months of age, boys had lower antibody concentrations than girls. Neutralizing measles virus antibody titers were above the threshold for protective immunity in all 78 samples analyzed. The measles virus antibody avidity indexes were high for all children. Conclusions. MMR induces similar antibody responses in 12-month-old children as compared to 18-month-old children, but in boys increasing age appears to improve the antibody responses.Peer reviewe

Impaired immunity and high attack rates caused by SARS-CoV-2 variants among vaccinated long-term care facility residents

Introduction: Long-term care facilities (LTCF) residents are at high risk for severe coronavirus disease 2019 (COVID-19), and therefore, COVID-19 vaccinations were prioritized for residents and personnel in Finland at the beginning of 2021. Methods: We investigated COVID-19 outbreaks in two LTCFs, where residents were once or twice vaccinated. After the outbreaks we measured immunoglobulin G (IgG) antibodies to severe acute respiratory syndrome coronavirus 2 spike glycoprotein, neutralizing antibody (NAb) titers, and cell-mediated immunity markers from residents and healthcare workers (HCWs). Results: In LTFC-1, the outbreak was caused by an Alpha variant (B.1.1.7) and the attack rate (AR) among once vaccinated residents was 23%. In LTCF-2 the outbreak was caused by a Beta variant (B.1.351). Its AR was 47% although all residents had received their second dose 1 month before the outbreak. We observed that vaccination had induced lower IgG concentrations, NAb titers and cell-mediated immune responses in residents compared to HCWs. Only 1/8 residents had NAb to the Beta variant after two vaccine doses. Conclusions: The vaccinated elderly remain susceptible to breakthrough infections caused by Alpha and Beta variants. The weaker vaccine response in the elderly needs to be addressed in vaccination protocols, while new variants capable of evading vaccine-induced immunity continue to emerge.Peer reviewe

Long-Lasting T Cell Responses in BNT162b2 COVID-19 mRNA Vaccinees and COVID-19 Convalescent Patients

Peer reviewe

Long-Lasting T Cell Responses in BNT162b2 COVID-19 mRNA Vaccinees and COVID-19 Convalescent Patients

The emergence of novel variants of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has made it more difficult to prevent the virus from spreading despite available vaccines. Reports of breakthrough infections and decreased capacity of antibodies to neutralize variants raise the question whether current vaccines can still protect against COVID-19 disease. We studied the dynamics and persistence of T cell responses using activation induced marker (AIM) assay and Th1 type cytokine production in peripheral blood mononuclear cells obtained from BNT162b2 COVID-19 mRNA vaccinated health care workers and COVID-19 patients. We demonstrate that equally high T cell responses following vaccination and infection persist at least for 6 months against Alpha, Beta, Gamma, and Delta variants despite the decline in antibody levels.</p