+/- interazione. Attivazione del sistema immunitario con. Rapida e completa espulsione del patogeno

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1 Patogeno interazione Ospite Rapida e completa espulsione del patogeno Attivazione del sistema immunitario con +/- Infezione acuta e successiva eliminazione del patogeno ++ Persistenza del patogeno (latenza e/o induzione di una patologia cronica) Pressione selettiva esercitata dal sistema immunitario sul patogeno

2 Nel corso della co-evoluzione con l ospite, i patogeni hanno acquisito strategie per evadere l immunità innata ed adattativa Esempi di strategie: Dormancy per rendersi poco visibili -produzione minima di proteine (herpesvirus) -integrazione del DNA nel genoma dell ospite (retrovirus) -quiescenza dei micobatteri

3 I patogeni hanno imparato ad evadere l immunità innata ed acquisita nel corso della co-evoluzione con l ospite Esempi di strategie: Sequestration ovvero occupare siti speciali -invasione dei globuli rossi da parte del Plasmodio della malaria -colonizzazione della cistifellea da parte di S. enterica Typhi -uso da parte di HIV delle cellule dendritiche per il trasporto dalle mucose ai linfonodi

4 HIV usa le cellule dendritiche come cavallo di Troia per il trasporto dalle mucose ai tessuti linfoidi DC immatura Legame di gp120 a DC-SIGN Internalizzazione e trasporto al compartimento endosomale???

5 Struttura di HIV ed infezione cellulare polimorfismi dell envelope e corecettori utilizzati Varianti R5 (M-tropiche) usano come corecettore CCR5 ed infettano DC, macrofagi e cellule T CD4+ Varianti X4 (T-tropiche) usano come corecettore CXCR4 ed infettano preferibilmente i linfociti T CD4+

6 Meccanismo di ingresso di HIV nella cellula Mechanism of HIV entry into a cell. In the model depicted, sequential conformational changes in gp120 and gp41 are induced by binding to CD4. These changes promote binding of the virus to the coreceptor (a chemokine receptor) and fusion of the HIV-1 and host cell membranes. The fusion peptide of activated gp41 contains hydrophobic amino acid residues that mediate insertion into the host cell plasma

7 Ciclo biologico di HIV

8 L interazione dei patogeni con le DC è mediato da recettori di vario tipo e promuove le risposte immunitarie ma alcuni patogeni possono sabotare i pathways di attivazione e maturazione DC immatura C-type lectins and Tolllike receptors: pathogen receptors on dendritic cells. For the recognition of microorganisms, immature dendritic cells (DCs) express Toll-like receptors (TLRs) and C-type lectins that bind specific pathogen components and carbohydrate structures, respectively. After recognition by TLRs a signaltransduction cascade is induced, which through the activation of nuclear factor-b (NF-B) results in the upregulation of expression of co-stimulatory molecules and adhesion molecules, and the production of cytokines, leading to DC maturation. The recognition of pathogens by C-type lectins leads to internalization of pathogens and intracellular processing for presentation by MHC class I and II molecules to T cells. TCR, T-cell receptor.

9 DC-SIGN: recettore lectinico di tipo C espresso da DC e macrofagi DC-SIGN lega: HIV (gp120) Virus Dengue HCV Virus Ebola CMV Mycobacterium tuberculosis Candida Albicans Helicobacter pylori Questi recettori appartengono alla famiglia dei PRR (pathogen recognition receptor) These receptors permit interactions with pathogens and endogenous soluble proteins as well as cell-surface ligands expressed by T cells and anatomically distinct endothelial cells, such as those found in secondary lymphoid organs. Langerin, a type-ii C-type lectin exclusively expressed by Langerhans cells, binds mannosetype ligands and delivers material to unique Birbeck granules. DC-SIGN another type-ii C-type lectin is expressed by both macrophages and DCs. It interacts with endogenous molecules, such as ICAM-2, on endothelial cells as well as ICAM-3 on T-cells, mediating intercellular adhesion. In addition, DC-SIGN binds pathogen-associated mannose-type carbohydrates found on viruses, bacteria and fungi. Multimerisation of DC- SIGN and other such receptors at the cell surface might facilitate high-affinity ligand binding. DC-SIGN=Dendritic Cell-Specific Intercellular adhesion molecule-3-grabbing Non-integrin

10 Struttura di DC-SIGN (carbohydrate recognition domain) C-type lectins are transmembrane proteins that act as cell-adhesion receptors, are involved in the regulation of signalling pathways and recognize specific carbohydrate structures that are present on self antigens and pathogens.

11 HIV usa DC-SIGN per penetrare nelle DC senza essere degradato e favorire la trasmissione ai linfociti T HIV-1 subverts intracellular processing by dendritic cells through DC-SIGN. a DC- SIGN (dendritic cell (DC)-specific intercellular adhesion molecule-grabbing nonintegrin) is expressed by immature DCs in mucosal tissues and lymph nodes, and by DC precursors in the blood. HIV-1 is captured by DC-SIGN that is expressed by DC precursors in the blood after infection or by immature DCs at mucosal entry sites during sexual transmission. DC-SIGNbound HIV-1 enters the cell, but escapes internalization into lysosomal compartments and recycles back to the cell surface. By hiding intracellularly in DCs, HIV-1 is protected during migration to the lymphoid tissues. On arrival at lymphoid tissues, DCs transmit HIV-1 to CD4+ T cells in trans, resulting in productive HIV-1 infection of CD4+ T cells. b High concentrations of HIV-1 allow viral infection of DCs that results in the production of HIV-1 by DCs, which subsequently infect T cells. Sequestration of HIV-1 by DC-SIGN can allow cis-infection of DCs by presenting the infectious virus to CD4 and co-receptors to allow efficient infection of DCs. c C-type lectins function as antigen receptors to internalize antigen into lysosomes to enhance antigen presentation by MHC class I and II molecules. It remains to be determined whether capture of HIV-1 by C-type lectins results in the activation of DCs and presentation of viral antigen by MHC molecules. CCR5, CC chemokine receptor 5; TCR, T-cell receptor.

12 HIV Infection

13 Langerina e DC-SIGN hanno un ruolo opposto nella protezione e trasmissione di HIV Cellula di Langerhans Epidermica (LC) Cellula dendritica-dc-sign+ Localizzazione delle cellule di Langerhans (LCs) e delle DC- SIGN+-DC negli epiteli delle mucose genitali

14 Immune evasion by Mycobacterium Tuberculosis

15 Persistenza del mycobacterium tuberculosis Th1 Th17 IL2 (a) Infecting mycobacteria taken up by alveolar macrophages in the lung resist killing by subverting phagosome maturation and by the protective effect of their lipid-rich cell wall. (b) Inflammatory signaling in response to mycobacterial components results in the recruitment of TH1 T cells. T cellmediated activation of macrophages enhances their ability to control mycobacteria. (c) Remaining viable mycobacteria are sequestered within a granuloma made up of macrophages and a variety of T cell subsets. (d) M. tuberculosis is able to persist in an asymptomatic form within the host over many decades. It is likely that mycobacteria are held in a nondividing or slowly dividing state in open lesions or in closed lesions walled-off by fibrosis. (e) Reduced immunity is associated with reactivation disease. Lack of immunosurveillance may stimulate renewed replication of mycobacteria in open lesions. For mycobacteria in closed lesions, liquefaction and breakdown in the absence of immune surveillance will result in disease. Once the disease process is underway, immunopathology contributes to tissue damage and ultimately efficient aerosol transmission to a new host.

16 Mycobacterium tuberculosis evade la risposta immunitaria utilizzando diversi meccanismi ureasi E B A C D

17 DC-SIGN signaling modulates TLR signaling during M. tuberculosis infection La produzione simultanea di IL10 e IL12 da parte delle DC disturba il differenziamento dei linfociti T naive verso un fenotipo Th1 ma induce Th producenti IL10 Nucleus S276 IL6 IL10 IL12 DC-SIGN binds ligands such as mycobacteria. DC-SIGN induces RAF1 phosphorylation, which modulates TLR induced NF-κB activation. Upon TLR stimulation the canonical NF-κB subunit p65 is released from its inhibitor and translocates to the nucleus. Phosphorylated RAF1 induces p65 phosphorylation at Ser276 that functions as a binding site for the histone acetylase CBP. Acetylation of p65 induces enhanced and prolonged Il6, Il10 and Il12ab transcription. CBP, CREB binding protein; DC-SIGN, DC-specific ICAM3-grabbing nonintegrin; MyD88, myeloid differentiation primary response protein 88; NF-κB, nuclear factor κ B; IκBα, inhibitor of NF-κBα; TLR, Toll-like receptor. DC-SIGN and TLR4 might inhibit each other after the recognition of Mycobacterium tuberculosis. Ligation of DC-SIGN by the M. tuberculosis virulence factor mannosecapped cell-wall component lipoarabinomannan (ManLAM) reduces TLR4- triggered DC maturation and enhances the production of interleukin-10 (IL-10) disfavouring a TH1-cell-mediated response and survival of the pathogen.

18 Il M. tuberculosis sopprime l immunità cellulare mediata dalle DC producendo ManLAM solubile che lega DC-SIGN a DC-SIGN (dendritic cell (DC)-specific intercellular adhesion molecule-grabbing nonintegrin) captures Mycobacteria tuberculosis by binding the mannose-capped cell-wall component lipoarabinomannan (ManLAM). M. tuberculosis are targeted to the late endosomes/lysosomes, whereas HIV-1 escapes internalization to lysosomal compartments. M. tuberculosis infects macrophages through the mannose receptor and/or DCs through DC-SIGN. Macrophages/DCs that are infected with M. tuberculosis secrete the virulence factor ManLAM that binds to DC-SIGN on DCs that are attracted to the inflammatory site. b Recognition of M. Tuberculosis by Toll-like receptors (TLRs) expressed by DCs results in the activation of nuclear factor-κb (NF-κB), leading to the activation/maturation of DCs, as observed by increased expression of co-stimulatory molecules CD80, CD83 and CD86. DC maturation leads to the production of inflammatory cytokines and immune activation to enhance T-cell responses to eliminate the pathogen. c Increased secretion of ManLAM by infected macrophages or DCs targets DC-SIGN and results in inhibitory signals that interfere with the TLR-activating stimuli that lead to DC maturation. The ManLAM DC-SIGN interaction results in inhibition of DC maturation and induction of the immunosuppressive cytokine interleukin-10 (IL-10), thereby preventing an efficient cellular immune response against M. tuberculosis infection.

19 Il micobatterio induce produzione di arginasi sia in cellule infettate che non infettate inibendo la sintesi di ossido nitrico Data form mouse models MyD88-dependent arginase induction prevents nitric oxide production in both mycobacteria-infected and - uninfected macrophages Activation of myeloid differentiation primary response protein 88 (MYD88) signalling by mycobacteria (at least in part through TLR2) induces CCAAT/enhancer-binding protein β (C/EBPβ)-mediated induction of interleukin-6 (IL-6), IL-10, and granulocyte colony-stimulating factor (GCSF) production. These signal transducer and activator of transcription-3 (STAT3)- activating cytokines act in both autocrine and paracrine manners to induce arginase 1 (Arg1) expression which is partially dependent on C/EBPβ. The produced arginase can inhibit inducible nitric oxide synthase (inos) activity through competition for the common substrate arginine. The MYD88 pathway for arginase production was shown to confer a survival benefit for mycobacteria in vivo and is thought to counteract pathways that activate nitric oxide production, such as TLR4. Nat Rev Immunol Mar;11(3):

20 Strategie adottate da S. enterica Typhi per la persistenza nell ospite e differenze con S. enterica Typhimurium Local acute inflammation with gastroenteritis and diarrhea Systemic infection reservoir On the left of the figure, the acute infection (human gastroenteritis) mediated by S. enterica Typhimurium involves bacteria replicating freely in the intestine lumen and using multiple attachment factors (represented by multicolored tips or fimbriae). S. enterica Typhimurium targets both enterocytes and M cells for invasion, but is stopped at the mesenteric lymph nodes. Neutrophils are quickly attracted to the invasion site and inflammation follows, leading to diarrhea. S. enterica Typhi has dispensed with many attachment and shedding factors and may preferentially target a limited number of host cell types that favor dissemination to deeper tissues. S. enterica Typhi can persist in the bone marrow for extended periods and in the gall bladder for life. T, T cell; B, B cell.

21 Tessuti linfoidi associati alle mucose: placche del Peyer dell intestino tenue

22 Salmonella typhimurium oltrepassa la barriera intestinale utilizzando più vie e determina una forte risposta infiammatoria locale NFkB Citochine e chemochine infiammatorie Invece, Salmonella typhi utilizza solo le cellule M

23 Meccanismi di regolazione dell immunità innata nell intestino

24 Le cellule M sono cellule specializzate dell epitelio intestinale

25 Variazioni antigeniche Meccanismo adottato da virus (HIV, virus dell influenza) o da batteri (streptococco, stafilococco, meningococco, borrelia burgdorferi, bordetella pertussis, neisseria gonorrhea) o da protozoi (tripanosomi) Conseguenze: Evasione della risposta umorale per -mancato riconoscimento da parte degli anticorpi Evasione della risposta cellulo-mediata per -interferenza con la proteolisi e con la produzione dell antigene -mancato legame alle molecole MHC -mancato riconoscimento da parte del TCR dei linfociti T -creazione di APL (altered peptide ligand)

26 Variazioni antigeniche del virus dell influenza di tipo A Lipid envelope Mutazioni puntiformi antigenic drift Anticorpi neutralizzanti contro la emoagglutinina bloccano il legame con la cellula Riarrangiamento antigenic shift La variazione antigenica si ha quando sono scambiati segmenti di RNA tra ceppi virali in un ospite intermedio antigenic drift antigenic shift Le glicoproteine coinvolte sono: l emoagglutinina la neuroaminidasi (sialidasi) small mutations new strain

27 Generazione di nuovi ceppi di virus influenzali causata da ricombinazione genetica Antigenic shift Pandemie del: 1918 (spagnola) 1957 (asiatica) 1968 (Hong Kong influenza) 2009 (febbre suina)

28 Sierotipi diversi di Streptococcus pneumoniae: un caso di variazione antigenica 84 diversi sierotipi di Streptococcus pneumoniae agente della polmonite batterica

29 I Tripanosomi africani (Trypanosoma rhodesiense e brucei) e le variazioni della glicoproteina di supeficie Es. di variazione antigenica 1000 varianti di VSG 1 genevsg La variazione di VSG è il risultato di un processo di conversione genica. Un gene inattivo è copiato e trasposto nel sito di espressione attivo in posizione telomerica 2 genevsg 3 genevsg Il soggetto infettato mostra ondate successive di parassitemia VSG= glicoproteina variante-specifica