host immunity and vaccines against bacterial meningitis
TRANSCRIPT
HOST IMMUNITY
AND VACCINES AGAINST
BACTERIALMENINGITIS
• Pathophysiology of bacterial meningitis Host factors Agent factors Host immunity (humoral, cell-mediated)
• Vaccines for Hemophilus influenzae Streptococcus pneumoniae Neiserria meningitidis Streptococcus agalactiae
• Future insights
• MENINGITIS: one of the major causes of infection-related deaths worldwide.
• 30–50% of the survivors sustain neurological sequelae. (Pomeroy et al. N Eng J Med 1990;320:1651-56)
• Major morbidity and mortality: neonates and children
• Pathogenesis depends on complex bacterial-host interactions.
• The correct understanding of the disease pathogenesis and host immunity may be of help to formulate therapeutic strategies and vaccines.
• Major bacterial pathogens: Account for >80% of the cases Hemophilus influenzae Streptococcus pneumoniae Neisseria meningitidis
• H. influenzae: incidence decreasing since the introduction of Hib vaccine in late 1980
• S. pneumoniae: Peak rates of infection in extremes of age: <2 years and
elderly High rates associated with basilar skull fracture,
immunocompromised state (e.g. splenectomy, multiple myeloma)
90 serotypes recognized, with a limited number accounting for a majority of invasive pneumococcal disease
N.meningitidis: • Only bacterium capable of generating epidemics of meningitis• 13 serotypes defined on the basis of capsular antigens (A, B, C,
W-135 and Y are responsible for severe cases)
A: Africa (Meningitis belt)
B, C and Y: endemic
meningitis in industrialized
countries
B: severe persistent
meningitis in Latin America
(Cuba, Columbia, Chile, Brazil)
and New Zealand
W-135: In Haji pilgrims and outbreaks in Burkina Faso (2002-03)
(www.meningvax.org)
Pathogenesis of Bacterial Meningitis
BACTERIAL FACTORS
• Lipopolysaccharide (capsule)
• Cell wall components Teichoic and lipoteichoic acid Peptidoglycan Outer membrane proteins
• Bacterial proteins IgA protease Pneumolysin
HOST FACTORS• Humoral immune response
Secretory IgA Anticapsular antibodies
• Cell mediated immune response Activation of macrophages Release of inflammatory mediators (e.g. cytokines,
interferons) Apoptosis and necrosis
• Complement pathway Alternate complement pathway Role of membrane attack complex
(Tunkel AR, Scheld W. Clin Micro Rev 1993;6:118-36)
Mucosal colonization
Survival and multiplication in blood
Pleocytosis and cytokine release
Penetration of BBB
Neuronal death(Kim KS. Nat Rev Neurosci 2003;4:376-85)
Time(Hours
postinfection)
Pathophysiologic events Clinical symptoms
0 Bacteria and bacterial products accumulate in CSF
None
4 Release of inflammatory mediators and cytokines
Fever
8–24 Blood-brain barrier disruption; development of cerebral edema;transendothelial migration of leukocytes; more proinflammatoryand toxic mediators; followed by impaired cerebralblood flow, elevated intracranial pressure, and vasculitis
Elevated CSF protein; meningism/neck stiffness;elevated CSF leukocytosis; systemiccomplications; altered mental status,focal symptoms, and seizures
24–48 Neuronal injury Focal symptoms; hearing loss; paralysis; cognitiveimpairment; death
(van der Flier et al. Clin Micro Rev 2003;16:415-429)
PATHOGENIC EVENT
BACTERIAL FACTORS HOST FACTORS
Mucosal colonization
•Fimbriae•Polysaccharide capsule•IgA protease•Bacteriocin
•Mucosal epithelium•Secretory IgA •Ciliary activity•Anticapsular antibodies
Intravascular survival
Polysaccharide capsule •Complement activation•Organism specific antibodies
Meningeal invasion •Fimbriae •Association with monocytes•Platelet activating factor receptor•Pneumococcal choline binding receptor A
Blood brain barrier
Survival in subarachnoid space
Polysaccharide capsule Poor opsonic activity
MUCOSAL COLONIZATIONFimbriae
N. meningitidis adhere to nasopharyngeal
epithelial cells and then transported
across within a phagocytic vacuole Two types of fimbriae in H. influenzae
(a- anterior nasopharynx,
b-posterior nasopharynx) and
transport through breakdown in tight junction
between epithelial cells)
Capsule H. influenzae type B: the most virulent
serotype S. pneumoniae : in-vivo capsular
transformation enhances the infection
Antibodies Natural mucosal antibodies e.g. IgA
may decrease the rate of
nasopharyngeal colonization IgA protease by Neisseria
Hemophilus
S. pneumoniae
Role of other bacterial components Lipopolysaccharide Peptidoglycan Teichoic acid
INTRAVASCULAR
SURVIVAL• Capsule : inhibition of
neutrophil phagocytosis and
resistance to complement-
mediated bactericidal activity• S. pneumoniae:
Lysed by activation of
alternate complement
pathway by C3• N. meningitidis:
Susceptible to attack by
membrane attack
complexes C5b-9
(Kuby Immunology 5th ed.)
MENINGEAL INVASIONGoverned by
High levels of bacteria in blood
Sites of CNS invasion
Dural venous sinuses
Cribriform plate
Choroid plexus
Adherence through fimbriae
Ascent of the bacteria through monocytes “TROJAN HORSE HYPOTHESIS”
Transcytosis through microvascular endothelial cells
Bacterial components Lipopolysaccharide
Outer membrane proteins
BACTERIAL SURVIVAL IN SUBARACHNOID SPACE AND ITS INFLAMMATION
• Prostaglandins (PGE2, prostacyclin)
• Interleukins (IL1b, IL6, IL8, IL12, IL16)• Interferon-g• TNF-a• Platelet activating factor• Macrophage inflammatory products 1 & 2• Leukocyte integrins• Leukocyte selectins• ICAM 1 • Endothelial leukocyte adhesion molecule 1• Reactive nitrogen intermediates• Peroxynitrite
BLOOD BRAIN BARRIER
• Adjacent endothelial cells are fused together by tight junctions that prevent intracellular transport
• Rare or absent pinocytotic vacuoles
• Abundant mitochondria
• Separation of tight junctions
• Increase in pinocytotic vesicle formation
• Inflammatory cytokines (IL-1 and TNF)
• Matrix metalloproteinases induce alterations in BBB by their endopeptidase activity
Features of BBB
RAISED INTRACRANIAL PRESSURE
Vasogenic edema Interstitial edema
Cytotoxic edema
Increased permeability of BBB
Swelling of cellular elements of brain by the release of toxic mediators from bacteria or neutrophils
Obstruction to the flow of CSF
Alteration in cerebral blood flow and ischaemia
NEURONAL INJURY
• Cell necrosis and damage to
cell membrane through free O2 radicals
• Apoptosis Apoptosis inducing factor (AIF) Pneumolysin Activation of PARP, poly (ADP-ribose) polymerase Caspase-3
• Reactive N2 intermediates
Nitric oxide Excitatory amino acids (glutamate, aspartate, glycine,
taurine, alanine) Peroxynitrite
(Koedel U. Lancet Infect Dis 2002;2:721–36)
VACCINES FOR MENINGITIS!!!!
Choice of vaccine: Polysaccharide or protein
conjugate??
TYPE OF VACCINE POLYSACCHARIDE PROTEIN CONJUGATE
T-cell dependent immunological function X
Effect on young children and infants X
Immunological memory and long term protection X
Reduction of nasopharyngeal
colonization
X
Herd immunity X
Haemophilus influenzae Type b (Hib) Vaccine
• Conjugated vaccines where the Hib capsular polysaccharide (polyribosyl ribitol phosphate or PRP) is conjugated with CRM197
• Universal immunization for children aged <5 years
• High-risk indications for children aged ≥5 years Immune system disorders (HIV/AIDS) treatment with drugs such as long-term steroids cancer treatment with x-rays or drugs bone marrow or organ transplant damaged spleen or no spleen.
PNEUMOCOCCAL VACCINES
Pneumococcal polysaccharide vaccine (23-valent)
PNEUMOVAX
Serotypes covered: 1, 2, 3, 4, 5, 6B, 7F, 8, 9N, 9V, 10A, 11A, 12F, 14, 15B, 17F, 18C, 19F, 19A, 20, 22F, 23F, 33F.
Dosing:0.5mL IM
Pneumococcal conjugate vaccine
PCV 7: 4, 6B, 9V, 14, 18C, 19F and 23 linked to CRM 197
Dosing: 0.5mL IM
PCV 13:1, 3, 4, 5, 6A, 6B, 7F, 9V, 14, 18C, 19A, 19F, and 23F conjugated to CRM197
PPV23
• 70% efficacy against
prevention of invasive pneumococcal
disease in the high-risk population but offers no protection
against non-bacteremic pneumonia/otitis media.
• Not more than two life time
doses are recommended as repeated doses may cause
immunologic hyporesponsiveness.
PCV 7 PCV 13
Healthy children
• PCV 7 is routinely given to infants as a series of 4 doses, one dose at each of these ages: 6 weeks, 10 weeks, 14 weeks, and a booster at 15-18 months.
• Catch up vaccination 6-12 months: 2 doses 4-8 weeks apart and 1 booster
at 15-18 months 12-23 months: 2 doses 8 weeks apart 24-59 months: single dose
(www.iapcoi.com)
High risk children
sickle cell disease, a damaged spleen or no spleen, cochlear implants, cerebrospinal fluid (CSF) leaks, HIV/AIDS or other diseases that affect the immune system
(such as diabetes, cancer, or liver disease), or chronic heart or lung disease or children who take medications that affect the immune
system, such as chemotherapy or steroids. Chronic renal/cardiac/hepatic failure
(www.iapcoi.com)
New antigens being identified……
• Cbp (Choline binding protein)
• Ply (Pneumolysin)• LytA (Autolysin)• PsaA (Pneumococcal
surface adhesin A) • PspA (Pneumococcal
surface protein A)
(Kadioglu A. Nat Rev Microbiol 2008;6:288-301)
MENINGOCOCCAL VACCINES
Meningococcal polysaccharide
vaccine (MENOMUNE)
Meningococcal conjugate vaccine (MENACTRA and MENVEO)
(www.cdc.gov)
Meningococcal PolysaccharideVaccine (MPSV) - Menomune
• Quadrivalent (serogroups A, C, Y, W-135)• Approved for persons 2 years of age and older• Administered by subcutaneous injection• Recommendations for use:
Individuals who are at elevated risk aged over 55 years Persons aged 2-55 years if there is a contraindication or
precaution to receiving MCV, such as persons with a history of Guillian-Barre syndrome.
(www.cdc.gov)
Meningococcal ConjugateVaccine (MCV)
• Quadrivalent (serogroups A, C, Y, W-135) conjugated to diphtheria toxoid
• MENACTRA approved for persons 2 through 55 years of age
• MENVEO approved for persons 11 through 55 years of age• Administered by intramuscular injection• Recommendations:• Adolescents aged 13-18 years receive 1 dose of MCV4
– Young adolescents at the pre-adolescent visit (11–12 years old)
– All persons aged 13-18 years at the earliest opportunity
(www.cdc.gov)
• Groups that have elevated risk of meningococcal disease
College freshmen living in dormitories Microbiologists who are routinely exposed to isolates
of N. meningitidis Military recruits Persons who travel to, or reside in countries in which N.
meningitidis is hyperendemic or epidemic, particularly if contact with the local population will be prolonged
Persons who have anatomic or functional asplenia or terminal complement component deficiencies
(www.cdc.gov)
• Initiatives by Meningitis Vaccine Project (MVP) and WHO to launch meningococcus group A vaccine,
MenAfriVac in meningitis belt, Africa for 1 to 29 yrs old and produced by Serum Institute of India, Ltd.
(www.meningovax.org)
Vaccines for Group B meningococcus
• Failure as the group B capsular
polysaccharide resembles human
neural cellular adhesion molecules
• Focus of attention has been Cell surface protein antigens contained in
OUTER MEMBRANE VESICLES Identification of new antigens as candidate vaccines by
REVERSE VACCINOLOGY
2
(Fraser CM. A genomics-based approach to biodefence preparedness. Nat Rev Gen 2004:5:23-33)
Potential vaccine candidates for Grp BPROTEIN FUNCTION
Neiserrial surface protein A (NspA) Immunogenic surface protein
PorA (class 1 protein) Cation porin
PorB (class 2/3 protein) Anion porin, induces immunity
Adhesion penetration protein (App) Autotransporter, induces antibodies after infection
Ferric binding protein (FbpA) Iron binding
Lactoferrin binding protein (LbpA) Lactoferrin binding
Opacity associated protein (OpA; class 5)
Adhesion, invasion
OpcA (Opc; class 5c) Invasion, adhesion
Transferrin binding protein A&B(TbpA, TbpB)
Iron acquisition from transferrin,
Pilin Adhesion
(Segal S, Pollard AJ. British Medical Bulletin 2004;72:65–81)
Vaccines for Streptococcus agalactiae
• Predominant cause of neonatal meningitis• Prophylactic antenatal antibiotic therapy is the main
preventive strategy• Nine serotypes• Conjugate vaccines have been prepared against the most
prevalent GBS serotypes in the USA (types Ia, Ib,II, III and V) and Japan (types VI and VIII)
• Whole-genome sequencing of serotypes Ia, III and V has offered new insights into GBS virulence, with potential vaccine candidates including capsular polysaccharide, β-haemolysin, C5a peptidase, adhesins and immunogenic surface proteins (Maione D et al. Science 2005;309:148-150)
• Adequate infrastructure for vaccine delivery and production in resource-poor countries with the highest meningitis burden
• Development of effective vaccination against group B meningococcus remains a considerable challenge
• Implementation of Hib vaccine in many resource-poor countries where disease burden is highest
• Tackling complete serotype representation and serotype replacement in pneumococcal vaccines
• Advances in the vaccine development through the development of genome-based strategies
References• Barocchi MA, Censini S, Rappuoli R. Vaccines in the era of genomics: The pneumococcal challenge.
Vaccine 2007;25:2963–73.• Bogaert D, Hermans PWM, Adrian PV, Rümke HC, de Groot R. Pneumococcal vaccines: an update on
current strategies. Vaccine 2004;22:2209–20.• Fraser CM. A genomics-based approach to biodefence preparedness. Nat Rev Gen 2004;5:23-33. • Girard MP, Preziosi MP, Aguado MT, Kieny MP. A review of vaccine research and development:
meningococcal disease. Vaccine 2006;24:4692-700.• Kadioglu A, Weisser JN, Paton JC, Andrew PW. The role of Streptococcus pneumoniae virulence factors in
host respiratory colonization and disease. Nat Rev Microbiol 2008;6:288-301.• Kim KS. Pathogenesis of bacterial meningitis: from bacteraemia to neuronal injury. Nat Rev Neurosci
2003;4:376-85.• Koedel U, Scheld WM, Pfister HW. Pathogenesis and pathophysiology of pneumococcal meningitis. Lancet
Infect Dis 2002;2:721–36.• Maione D, Margarit I, Rinaudo CD, Masignani V, Mora M, Scarselli M et al. Identification of a universal group
B streptococcus vaccine by multiple genome screen. Science 2005;309:148-50.• Pomeroy SL, Holmes SJ, Dodge PR, Feigin RD. Seizures and neurological sequelae of bacterial meningitis
in children. N Eng J Med 1990;324:1651-56.• Segal S, Pollard AJ. Vaccines against bacterial meningitis. British Medical Bulletin 2004;72:65–81. • Tunkel AR, Scheld W. Pathogenesis and pathophysiology of bacterial meningitis. Clin Micro Rev 1993;6:118-
36.• van der Flier M, Geelen M, Kimpen JLL, Hoepelman IM, Tuomanen EI. Reprogramming the host response in
bacterial meningitis: how best to improve outcome. Clin Micro Rev 2003;16:415-29.• www.cdc.gov• www.iapcoi.com• www.meningvax.org