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IL SISTEMA IMMUNITARIO • IMMUNOLOGIA DERIVA DA IMMUNE • IMMUNE VUOL DIRE ESSERE LIBERO DA MALATTIE INFETIVE • L’IMMUNOLOGIA E’ LA DISCIPLINA CHE STUDIA I MECCANISMI DIFENSIVI CHE CI RENDONO IMMUNI O LIBERI DA MALATTIE INFETTIVE • CONDIVIDIAMO L’AMBIENTE CON I MICRORGANISMI

Evoluzione del sistema linfoide Spugne Molluschi, Tunicati e echinodermi Vertebrati Cellule mesenchimali Cellule linfoidi primitive Linfociti T e B Organi linfatici primari (timo) e secondari (noduli linfatici, linfonodi e milza)

Evoluzione del sistema immunitario fagocitosi Ig. M, Ig. G

Evoluzione del sistema immunitario Ig. M, Ig. G, Ig. A, Ig. D, Ig. E

RISPOSTA IMMUNITARIA INNATA e ADATTATIVA I meccanismi della risposta immunitaria INNATA sono la prima linea di difesa dell’organismo contro le infezioni. La risposta immunitaria ADATTATIVA si sviluppa invece in un secondo momento e consiste principalmente nell’attivazione dei linfociti.

IMMUNITA’ INNATA

Immunità innata E’’ costituita da una serie di meccanismi di difesa antichi, non specifici, presenti fin evoluzionisticamente dalla nascita di un individuo. Questi sono presenti già prima dell’esposizione all’antigene e rappresentano la prima vera barriera di difesa dell’organismo agli agenti patogeni.

Componenti Funzioni principali Barriere Strato epiteliale Prevenzione dell’entrata dei microbi Defensine Uccisione dei microbi Linfociti intraepiteliali Uccisione dei microbi Cellule effettrici circolanti Neutrofili Fagocitosi e uccisione dei microbi Macrofagi Fagocitosi e uccisione dei microbi, Secrezione di citochine che stimolano infiammazione Cellule NK Lisi delle cellule infettate, attivazione dei macrofagi Proteine effettrici circolanti Complemento Uccisione e opsonizzazione microbi, Attivazione dei leucociti Lectina che lega il mannosio (collectina) Opsonozzazione microbi, attivazione del complemento (via lectinica) Proteina C-reattiva (pentraxina) Opsonizzazione microbi, attivazione complemento Fattori di coagulazione Isolano I tessuti infetti Citochine TNF, IL-1, chemochine Infiammazione IFN-a, -b Resistenza a infezioni virali IFN-g Attivazione macrofagi IL-12, IL-18, IL-23 Produzione di IFN-g da cellule NK e T IL-15 Proliferazione cellule NK IL-10, TGF-b Controllo dell’infiammazione

Vie di infezione dei patogeni

BARRIERE EPITELIALI Gli epiteli presenti nel luogo d’entrata dei microbi esercitano la funzione di barriera fisica, producono sostanze antimicrobiche e contengono linfociti intraepiteliali che uccidono microbi e le cellule infette

Barriere epiteliali intrinseche contro le infezioni Meccaniche üCellule epiteliali unite dalle giunzioni strette. üMovimento del muco mediante le ciglia Chimiche üAcidi grassi üEnzimi: lisozima, pepsina üp. H üPeptidi antibatterici Microbiologiche üLa flora compete per i nutrienti e per l’attacco all’epitelio e può produrre sostanze antibatteriche.

CELLULE E TESSUTI DEL SISTEMA IMMUNITARIO

Cellule dell’ Immunità Innata • Granulociti (Fagocitosi ) • Monociti (Fagocitosi ) • Macrofagi (Fagocitosi ) • Cellule dendritiche Cellule Natural Killer (NK o LGL): Citotossicità

Numero assoluto e percentuali dei leucociti nel sangue (Esame emocromocitometrico completo) Globuli Bianchi: 4000 -6000/mm 3 Granulociti Neutrofili: >55% Granulociti Basofili: 1% Granulociti Eosinofili: 1% Monociti: 3% • Linfociti T e B: 20% • Linfociti non T non B (NK): 20%

Granulocita neutrofilo

Morphology of neutrophils. The light micrograph of a blood neutrophil shows the multilobed nucleus, because of which these cells are also called polymorphonuclear leukocytes, and the faint cytoplasmic granules. Downloaded from: Student. Consult (on 23 September 2008 03: 22 PM) © 2005 Elsevier

Figure 2. 5 At the ultrastructural level, the azurophilic (primary) granules are larger than the secondary (specific) granules with a strongly electron-dense matrix; the majority of granules are specific granules and contain a variety of toxic materials to kill microbes. A pseudopod (to the right) is devoid of granules. Arrows indicate nuclear pores. (Go, Golgi region) Inset: A mature neutrophil in a blood smear showing a multilobed nucleus. × 1500. (From Zucker-Franklin D, Grossi CE, eds. Atlas of blood cells: function and pathology, 3 rd edn. Milan: Edi Ermes; 2003) Downloaded from: Student. Consult (on 2 April 2008 09: 53 AM) © 2005 Elsevier

Granulocita basofilo

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Figure 2. 8 Ultrastructural analysis shows a segmented nucleus (N) and the large cytoplasmic granules (G). Arrows indicate nuclear pores. × 11 000. (Adapted from Zucker-Franklin D, Grossi CE, eds. Atlas of blood cells: function and pathology, 3 rd edn. Milan: Edi Ermes; 2003) Inset: This blood smear shows a typical basophil with its deep violet-blue granules. × 1000. Downloaded from: Student. Consult (on 2 April 2008 09: 53 AM) © 2005 Elsevier

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Morphology of mononuclear phagocytes. A. Light micrograph of a monocyte in a peripheral blood smear. B. Electron micrograph of a peripheral blood monocyte. (Courtesy of Dr. Noel Weidner, Department of Pathology, University of California, San Diego. ) C. Electron micrograph of an activated tissue macrophage showing numerous phagocytic vacuoles and cytoplasmic organelles. (From Fawcett DW. Bloom & Fawcett's Textbook of Histology, 12 th ed. Chapman & Hall, 1994. With kind permission of Springer Science and Business Media. ) Downloaded from: Student. Consult (on 23 September 2008 02: 30 PM) © 2005 Elsevier

Figure 2. 4 Ultrastructure of a monocyte showing the horseshoe-shaped nucleus, pinocytotic vesicles (PV), lysosomal granules (G), mitochondria (M), and isolated rough endoplasmic reticulum cisternae (E). × 8000. (Courtesy of Dr B Nichols) Inset: Light microscope image of a monocyte from the blood. × 1200. Downloaded from: Student. Consult (on 2 April 2008 09: 53 AM) © 2005 Elsevier

Maturation of mononuclear phagocytes. Mononuclear phagocytes develop in the bone marrow, circulate in the blood as monocytes, and are resident in all tissues of the body as macrophages. They may differentiate into specialized forms in particular tissues. CNS, central nervous system. Downloaded from: Student. Consult (on 23 September 2008 02: 30 PM) © 2005 Elsevier

Circulating monocytes give rise to myeloid dendritic cells (distinct from plasmacytoid dendritic cells, which are thought to originate from distinct precursors), tissue macrophages, and osteoclasts. F 4/80 and FA/11 (macrosialin, the murine homolog of CD 68) are differentiation antigens of mouse macrophages and closely related cells. Downloaded from: Student. Consult (on 23 September 2008 02: 44 PM) © 2005 Elsevier

Resident tissue macrophage populations. Downloaded from: Student. Consult (on 23 September 2008 02: 44 PM) © 2005 Elsevier

Microglia are widely distributed in non-overlapping fields and show a dendritic morphology. (Courtesy of Dr Payam Rezaie) Downloaded from: Student. Consult (on 23 September 2008 02: 44 PM) © 2005 Elsevier

Recettori per i patogeni sulle cellule dell’immunità innata • Esistono numerose famiglie di recettori. • Queste molecole recettoriali riconoscono motivi molecolari comuni a molte sostanze presenti sulla superficie dei patogeni. • Il riconoscimento non è limitato o specifico per una sostanza ma allargato a gruppi di sostanze o molecole presenti sui microrganismi.

Figure 2 -3 Downloaded from: Student. Consult (on 23 September 2008 02: 30 PM) © 2005 Elsevier

Recettori per il riconoscimento dei microrganismi impiegati dai macrofagi e fagociti. Downloaded from: Student. Consult (on 23 September 2008 02: 30 PM) © 2005 Elsevier

The mannose receptor contains eight C-type lectin domains involved in binding to mannosylated carbohydrates and related glycoconjugates. It is related to a more broadly expressed endocytic receptor, ENDO 180. A distinct lectin domain located in the distal (C terminal) segment binds sulfated glycoconjugates. The β -glucan receptor (dectin-1) contains a single lectin domain and an intracellular immunoreceptor tyrosine-based activation motif (ITAM). DC-SIGN (another mannose-binding C-type lectin) has four associated lectin domains. Downloaded from: Student. Consult (on 23 September 2008 02: 44 PM) © 2005 Elsevier

Selected scavenger receptors are shown. Scavenger receptors of macrophages are responsible for the uptake of apoptotic cells, modified lipoproteins, and other polyanionic ligands (e. g. LPS and lipoteichoic acids [LTA]), as well as selected bacteria such as Neisseria spp. CD 163 is involved in endocytosis of hemoglobin-haptoglobin complexes. Downloaded from: Student. Consult (on 23 September 2008 02: 44 PM) © 2005 Elsevier

Mammalian TLRs: specificities, basic signaling mechanisms, and cellular responses. Ligands for TLRs are shown together with dimers of the TLRs that specially bind them. Note that some TLRs are expressed in endosomes and some on the cell surface (see Fig. 2 -7). The basic steps in TLR signaling, illustrated only for TLR 3 and TLR 4, are applicable to all TLRs. Further details about the signaling pathways are described in Box 2 -1. Downloaded from: Student. Consult (on 23 September 2008 02: 30 PM) © 2005 Elsevier

Cellular locations of pattern recognition molecules of the innate immune system. Some pattern recognition molecules of the TLR family (see Fig. 2 -7), such as TLRs 2, 4, and 5, are expressed on the cell surface, where they may bind extracellular pathogen-associated molecular patterns. Other TLRs are expressed on endosomal membranes, such as TLRs 3, 7, 8, and 9, all of which can recognize nucleic acids of microbes that have been phagocytosed by cells. Cells also contain cytoplasmic sensors of microbial infection (discussed later in the chapter), including the NLR family of proteins, which recognize bacterial peptidoglycans, and a subset of CARD family of proteins, which bind viral RNA. Downloaded from: Student. Consult (on 23 September 2008 02: 30 PM) © 2005 Elsevier

Effector functions of macrophages. Macrophages are activated by microbial products such as LPS and by NK cell-derived IFN-γ (described later in the chapter). The process of macrophage activation leads to the activation of transcription factors, the transcription of various genes, and the synthesis of proteins that mediate the functions of these cells. In adaptive cell-mediated immunity, macrophages are activated by stimuli from T lymphocytes (CD 40 ligand IFN-γ ) and respond in essentially the same way (see Chapter 13, Fig. 13 -14). Downloaded from: Student. Consult (on 23 September 2008 02: 30 PM) © 2005 Elsevier

Recettori per le opsonine • Recettori per il componente C 3 b del complemento. • Recettori per il frammento cristallizabile (Fc) delle Immunoglobuline Ig. G e Ig. M.

Pathogens, such as bacteria, are taken up by binding to opsonic receptors including the Fc receptor, complement receptors, and receptors for carbohydrate (MR). (2) The particle is engulfed and the phagosome forms (3). Acidification of the phagosome follows as toxic molecules (reactive oxygen and nitrogen intermediates) are pumped into the phagosome. The marker FA/11 is located in the phagosome membrane. (4) Lysosomes fuse with the phagosome, releasing proteolytic enzymes into the phagolysosome, which digest the bacteria. (5) On completion the membrane of the phagolysosome is disrupted. Antigenic fragments may become diverted to the acidic endosome compartment for interaction with MHC class II molecules and antigen presentation. The process induces secretion of toxic molecules and cytokines. Downloaded from: Student. Consult (on 23 September 2008 02: 44 PM) © 2005 Elsevier

La Fagocitosi

FAGOCITOSI E DISTRUZIONE INTRACELLULARE DEI MICROBI I microbi si possono legare a diversi recettori di membrana presenti sui fagociti; alcuni di questi recettori legano direttamente i microbi, altri invece legano i microbi opsonizzati. I microbi vengono internalizzati in fagosomi, che si fondono poi con i lisosomi per formare i fagolisosomi all’interno dei quali i microbi vengono uccisi dagli intermedi reattivi dell’ossigeno e dell’ossido nitrico.

Meccanismi di uccisione dei patogeni ØMeccanismi O dipendenti: produzione di ROS (radicali attivi dell’ossigeno) come l’ossigeno singoletto. Questo composto è poi in grado di produrre composti altamente battericidi come il perossido d’idrogeno e il radicale ossidrilico ØMeccanismi Ossigeno indipendenti: l’uccisione avviene tramite diverse sostanze contenute nei lisosomi: il lisozima, le proteine cationiche, le defensine e la lattoferrina. ØMeccanismi Azoto dipendenti: anche in questo caso si formano nei composti reattivi dell’azoto in grado di produrre composti battericidi.

RECETTORI E RISPOSTE DEI FAGOCITI I neutrofili e I macrofagi hanno recettori di membrana diversi per riconoscere I microbi, I prodotti microbici e sostanze prodotte dagli ospiti durante l’infezione. Questi recettori attivano delle risposte cellulari che hanno la funzione di stimolare l’infiammazione e eradicare I microbi.

Figure 1. 18 At a site of inflammation, tissue damage and complement activation cause the release of chemotactic peptides (e. g. chemokines and C 5 a), which diffuse to the adjoining venules and signal to circulating phagocytes. Activated cells migrate across the vessel wall and move up a concentration gradient of chemotactic molecules towards the site of inflammation. Downloaded from: Student. Consult (on 23 September 2008 03: 29 PM) © 2005 Elsevier

RECLUTAMENTO DEI LEUCOCITI Nel sito di infezione I macrofagi che hanno incontrato microbi iniziano a produrre citochine (TNF e IL-1) le quali attivano le cellule endoteliali dei vasi circostanti a produrre selectine, ligandi per le integrine e chemochine. Le selectine promuovono un debole legame sui leucociti (neutrofili) circolanti facendoli rotolare sulla parete; le integrine invece mediano una adesione più forte dei neutrofili e le chemochine ne aumentano l’affinità di legame, e stimolano l. a migrazione delle cellule dall’endotelio verso il sito di infezione. Neutrofili, monociti e linfociti T attivati circolanti usano essenzialmente questi stessi meccanismi per raggiungere il sito di infezione.