Bacterial evasion of host immunity

Transcription

1 Bacterial evasion of host immunity Gunnar Lindahl Lund University, Sweden and Copenhagen University, Denmark

2 A pathogen must evade attack by the immune system of the host innate immunity adaptive immunity

3 A pathogen must evade attack by the immune system of the host innate immunity adaptive immunity extracellular pathogens intracellular pathogens

4 A) Innate immunity # phagocytosis (recognition; killing) # complement # anti-bacterial peptides # TLRs/NLRs (proinflammatory cytokines) # apoptosis # autophagy

5 Phagocytosis is a major defense mechanism, in particular against extracellular Gram-positive bacteria Phagocyte (neutrophil)

6 Pathogens may inhibit the function of neutrophils by blocking their recruitment of by killing them # Streptococci secrete enzymes that degrade C5a or IL-8, thereby interfering with the recruitment of neutrophils # Staphylococci secrete small peptides (PSMs) that lyze neutrophils

7 Phagocytosis may be inhibited by a polysaccharide capsule Phagocyte

8 Even if the bacteria encounter a phagocyte and lack a capsule, they must be opsonized for efficient phagocytosis to occur Phagocyte

9 Opsonization is promoted by: Complement Immunoglobulin (Ig) activation C3b ic3b Fab Fc (Innate immunity) (Adaptive immunity)

10 Opsonization for phagocytosis: innate immunity Phagocyte Complement receptor (CR) ic3b

11 Opsonization for phagocytosis: innate immunity Phagocyte Complement receptor (CR) A bacterium may evade complement-mediated phagocytosis by blocking complement deposition

12 The complement system Classical pathway (CP) Lectin-pathway Alternative pathway (AP) - specific antibodies - MBL - spontaneous activation nonimmune activation - - amplification loop C3 C4b2a CP C3-convertase C3bBb AP C3-convertase C3b Opsonin MAC Amplification loop Membrane Attack Complex

13 Human complement regulators in the RCA family Lindahl et al, Curr Opin Immunol (2000)

14 The complement system Classical pathway (CP) Lectin-pathway Alternative pathway (AP) - specific antibodies - MBL - spontaneous activation nonimmune activation - - amplification loop C3 C4b2a C3bBb factor I CP C3-convertase AP C3-convertase factor I C4BP C3b Opsonin factor H MAC Amplification loop Membrane Attack Complex

15 Low-level continuous activation and the presence of specific inhibitors allows the complement system to distinguish between self and non-self

16 Many pathogens inhibit complement deposition by hi-jacking C4BP or factor H

17 C4BP (C4b-binding protein) A human plasma protein that inhibits the classical pathway C3 convertase α β = SCR/CCP module MW ~ 570,000 Da Conc. in plasma ~200 µg/ml

18 Many streptococcal M proteins hijack human C4BP, for protection against phagocytosis Complement activation via classical pathway C4BP Inhib. Carlsson et al, J Exp Med (2003) C3b M22

19 Examples of bacterial pathogens that hijack human C4BP or factor H, thereby blocking complement deposition Bacterium Streptococcus pyogenes (GAS) Neisseria meningitidis Moraxella catharralis Haemophilus influenzae Streptococcus pneumoniae Ligand C4BP C4BP, FH C4BP C4BP, FH FH Neisseria gonorrhoeae Borrelia burgdorferi C4BP FH

20 B) Adaptive immunity antigen uptake antigen presentation specific T cells adaptive immunity (cellular or humoral)

21 antigen uptake antigen presentation specific T cells adaptive immunity (cellular or humoral) inhibition of antigen presentation inhibition (via T-reg) evasion through antigenic variation

22 Hansen and Bouvier, Nat Rev Immunol (2009)

23 Baena and Porcelli, Tissue antigens (2009)

24 antigen uptake antigen presentation specific T cells adaptive immunity (cellular or humoral) inhibition of antigen presentation inhibition (via T-reg) evasion through antigenic variation

25 Antigenic variation Immunological change in a surface protein of a pathogen, allowing evasion of protective immunity Two strategies: a) Appearance of new variants during an infection b) Circulation of many stable variants (types) in the population

26 Antigenic variation: some well-known examples Pathogen Variable surface protein Plasmodium falciparum Trypanosoma brucei VSG PfEmp1 Neisseria gonorrhoeae Streptococcus pyogenes Pilin M protein HIV-1 Influenza virus gp120 Hemagglutinin

27 Aspects on antigenic variation # genetic mechanisms: shift and drift # the immunology of escape

28 Antigenic variation in Neisseria pili: antigenic shift Davidsen & Tønjum, Nature Rev Microbiol (2006)

29 Antigenic variation in three bacterial pathogens: antigenic shift Palmer et al., Cell. Microbiol. (2009)

30 Antigenic variation by epigenetic mechanisms in Giardia lamblia: role of RNA interference Prucca et al., Nature (2008) Ankarklev et al., Nat Rev Microbiol (2010)

31 Antigenic drift in HIV-1: sequence variability in the V3 loop of gp120 LaRosa et al., Science (1990)

32 Antigenic variation: genetic drift and shift (in a virus) Malim & Emerman, Cell (2001)

33 Antigenic variation and Alice in wonderland The most curious part of the thing was, that the trees and the other things round them never changed their places at all: however fast they went, they never seemed to pass anything. I wonder if all the things move along with us? thought poor puzzled Alice. (Lewis Carroll, 1872) Hedrick, Immunity (2004)

34 A classical problem How does immune pressure select for sequence variants? This is simple to understand for shift, much less clear for drift

35 Antigenic drift in HIV-1: sequence variability in the V3 loop of gp120 LaRosa et al., Science (1990)

36 Antigenic drift host receptor microbial adhesin immunity mutations mutation immune escape

37 Alternative model host receptor microbial adhesin immunity mutation immune escape

38 Science 326, 734 (2009)

39 Xu et al., Science 2010 Antigenic sites in influenza virus hemagglutinin

40 New model host receptor 1 immunity microbial adhesin mutation 1 causes very strong binding! immune host 2 1 in new naïve host: compensatory mutation 2 results in normal binding strength mutation 1

41 New model, continued Infection of new host: mutation 3 causes very strong binding - even in immune host immunity in new naïve host: compensatory mutation mutation 3

42 Science 326, 734 (2009)

43 C) Streptococcal M protein and evasion of host immunity

44 Two common diseases caused by Streptococcus pyogenes (Group A Streptococcus, GAS) Acute pharyngitis Impetigo

45 Global burden of S. pyogenes disease Superficial infections Pharyngitis and skin infections: > 700 million cases/year Severe infections > 500,000 deaths per year Carapetis et al., Lancet Infect Dis (2005)

46 The M protein of Streptococcus pyogenes M pos. M neg. Swanson et al., J Exp Med (1969)

47 J Exp Med 47, 91 (1928) Rebecca Lancefield ( )

48 Streptococcal M protein: some members of the family Smeesters et al, Trends Microbiol (2010)

49 Many M proteins hijack the human complement inhibitor C4BP: evasion of innate immunity C4BP inhibition complement deposition M protein S. pyogenes C contributes to phagocytosis resistance

50 Adaptive immunity: antibodies that inhibit C4BP-binding promote phagocytosis C4BP M protein Opsonization by antibodies and complement S. pyogenes phagocytosis

51 The pathogen s response: selection of mutants that still bind C4BP, but escape antibodies C4BP Hypervariable region (HVR) M protein bacterial survival S. pyogenes Darwinian evolution!

52 Extreme sequence variation in hypervariable regions (HVRs) that bind C4BP M2 M NSKNPVPVKKEAKLSEAELHDKIKNLEEEKAELFEKLDKVEEEHKKVE AEIKKPQADSAWNWPKEYNALLKENEELKVEREKYLSYADDKEKD M AEIKKPQADSAWNWPKEYNALLKENEEFKVEREKYLSYADDKEKD M ESSNNAESSNISQESKLINTLTDENEKLREELQQYYALSDAKEEEPRYKALR M60 M114 prth ESSTVKAESSTVKAESSTISKERELINTLVDENNKLMEERARHLDLIDNIREKDPQYRALRGENQD --NSKNPAPAPASAVPVKKEATKLSEAELYNKIQELEEGKAELFDKLEKVEEENK EGAKIDWQEEYKKLDEDNAKLVEVVETTSLENEKLKSENEENKKNLDKLSKD No residue identities! Persson et al, PLoS Pathogens (2006)

53 HVR Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Selection of protein variants with new HVRs

54 Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y (Y) Y Y Y

55 The hypothesis was analyzed for the M5 and M1 proteins The HVR is a major target for protective antibodies

56 Immunization of mice with M5 or M1 elicits a very weak anti-hvr response

57 Weak anti-hvr response in humans: invasive infections caused by M1-expressing S. pyogenes

58 Conclusion: The HVR of streptococcal M protein elicits a weak antibody response Working hypothesis: The C-terminal region actively interferes with the antibody response to the HVR: HVR (Y) inhib. YYYYYYY Y

59 Streptococcal escape from antibodies Healthy host Infected host Antigenic variation allows escape from preexisting antibodies and allows establishment of infection Weak anti-hvr response prolongs infection

60 Conclusion of M protein work Our data contradict the common assumption that the HVR of a virulence factor is immunodominant Two independent mechanisms allow S. pyogenes to evade antibodies against the HVR: antigenic variation and weak antibody response The two escape mechanisms work at different stages of an infection Weak antibody responses might be as important as antigenic variation in promoting bacterial virulence

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62 Acknowledgements Jonas Lannergård Mattias Gustafsson Johan Waldemarsson Margaretha Stålhammar-Carlemalm Anna Norrby-Teglund (Stockholm)

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