NATURAL IMMUNITY Immunology EPh Dr. habil. Kőhidai László Department of Genetics, Cell- and Immunobiology Semmelweis University

The immune response Natural (innate) Acquired (adaptive) Provides immediate defense Develops with time

Innate immunity First line defense Limited specifity Immediate response (no latency) Linear amplification No memory Cellular and humoral defense

Immume homeostasis Innate dendritic cell macrophage  T cell complement system CD5+ B cell antibacterial peptides NK cell granulocytes cytokines Adaptive T lymphocyte cytokines B lymphocyte antibodies

Pathogen Virus Viral RNA, DNA peptide Bacteria, fungi etc. Target Cell infected by virus MacrophageEpithelGranulo- cyte Comple ment Signal IL12 TNFaEndothelC3a C5a chemokines Effector NK cellPhagocytesDefensinsMAC- lysis Target destroyed Virus infected ell Bacteria, fungi Bacteria, fungiGram- bact. viruses

Soluble recognition molecules of innate immune system Defensinsbacteria, fungikilling Pentraxines C reactive protein (CRP)ECM protein, complement Serum amyloid protein (SAP) microbial cell wall (polysacch., nucl. acids) Collectines Mannose binding lectinsMicrobial cell wall complement Ficolin(phosphoryl choline, Surface active proteinssaccharides) Lipopolysaccharide bindingLPSLPS sens. proteins (LBP)

Barriers: skin, mucous membranes, secretions Cells: macrophages, neutrophils, NK cells, mast cells, dendritic cells Molecules: complement system MPS (mononuclear phagocyte system) First line defence

Mechanical: skin, mucous membranes, cough, sneeze Chemical: skin pH:  5,5  stomach pH: 1,2-3 Biological: in the mouth saliva contains antibacterial agents lysozyme lactoperoxidase lactoferrin antibody - IgA First line barriers in toothpaste

Limited specificity 3 strategies in recognition Pathogen non-self Altered self Characteristic markers of pathogens (missing in the host) Immunreaction is blocked in case of self markers (missing in microorganisms) Non healthy self markers Missing MHCI - NK cells active Missing C3 convertase – alternative complement activation starts Missing sialic acid – phagocytes, alternative complement activation Missing self

immunolfig02.html APOPTOSIS NK CELLS: dual receptor system Tumor or virus infected cell KIR/ KAR no MHC

Limited specificity 3 strategies in recognition Pathogen non-self Altered self Characteristic markers of pathogens (missing in the host) Immunreaction is blocked in case of self markers (missing in microorganisms) Non healthy self markers Missing self

Opsonic receptors: Fc and complement receptors Phagocytes have two types of receptors on their surfaces Pattern Recognition Receptors (PRRs)

Opsonization Facilitation of phagocytosis vs. 

complement protein antibody complement receptor Fc receptor phagocyte bacterium OPSONIZATION

Fc receptors b ind IgE h igh affinity receptor is expressed on mast cells and basophils role in allergy (low affinity receptor has regulatory function) Fcε receptors bind IgG facilitate phagocytosis (regulate B-cell activation) Fcγ receptors Fc region Immunoglobulin = Ig IgG

Fc receptor mediated phagocytosis

Complement protein antibody Complement receptor Fc receptor p hagocyte PAMP PRR Limited specificity bacterium OPSONIZATION

PAMP PRR pathogen-associated molecular patterns pattern recognition receptors pattern recognition Membrane receptors Intracellular receptor Secreted receptors

I. Scavenger receptors - CD14: LPS receptor II. Lectin receptors - macrophage mannose receptor III. Toll like receptors - carbohydrates, lipids, nucleic acids Membrane PRR

LPS receptor Gay et al. Nature Reviews Immunology, 2006

Nucleic acid and lipid/protein TLR ligands are recognized in different cellular compartments. Lipid or protein TLR ligands : recognized on the plasma membrane e.g. LPS, flagellin Nucleic acid TLR ligands: recognized by TLRs in the endosome. Toll-like receptors (TLR)

Intracellular cytoplasmatic PRRs RIG-I-like helicases (RLHs, RLR) recognize viral 5 ’ - Triphosphat e ssRNA -Nod-like Receptors (NLRs) recognize peptidoglycan constituent of Gram positive and Gram negative bacteria Nature Reviews Microbiology 5,

Brown GD. Dectin-1: a signalling non-TLR pattern-recognition receptor. Nat Rev Immunol Jan;6(1): Recognition – at multiple levels 5. Intracellular PRR 1. Secreted PRR 3.Membrane PRR 2.Opsonisation 4. Multiple recognition

Specificity of TLR Inflammatory respponses

- expression of receptors - release of mediators - internalization of bacteria - phagolysosome formation Main steps of macrophage activity

Immediate response (no latency)

NADPH-ox = NADPH oxidase SOD SOD = superoxide dismutase MPO = myeloperoxidase Microbicidal activity of professional phagocytes Superoxide: O 2 + e -  O 2 - Hydrogen peroxide:O e - + 2H+  H 2 O 2 Hydroxyl groups:H 2 O 2 + e - + 2H+  OH - + H 2 O

Takes place even whithout PHAGOCYTOSIS !

IL-1 TNF-  FEVER Fever is caused by exogenous (e.g. bacterial subst.) and endogenous pyrogenes (products of macrophages). - Major endogenous pyrogens: IL-1, IL-6, TNF-alpha - Minor endogenous pyrogens: IL-8, MIP-1, MIP-2, interferons Brain: Circumventricular organs

Commensal bacterial flora - all the natural bacteria that live on and in a healthy person ( skin, oral cavity, upper respertory tract, lower GI tract, the urogenital tract ) = cells - about bacteria living in the human gut - i n oral cavity e.g. Streptococcus species Benefit to the host: Compete with pathogens for colonization (by competing for nutrition and attachment sites to the epithelium)

Differential expression and compartmentalization of TLRs No TLR: commensal bacteria are tolerated – NO recognition TLR: Bacteria passing the epithelia Intracellular bacteria – intracellular TLR Nature Reviews Immunology 8, (June 2008)

All bacteria that cross the epithelium are recognized by immune cells

DANGER !!!

How antigens reach lymph node? Immature dendritic cell

Bridge between innate and adaptive immunity

Innate immunity Adaptive immunity Dendritic cell TLR COSTIMULATION : required for initial activation of T cells

Adaptive immune system NOT ONLY A SIMPLE FIRST LINE defence TLR based CONNECTION between natural and adaptive immunity

Nature Reviews Immunology 8, (April 2008) PAMP: Pathogen associated molecular pattern DAMP: Damage associated molecular pattern

Nature Reviews Immunology 8, (April 2008) Danger only in case of necrotic cell death ! !

RAGE: (Receptor for advanced glycation endproducts) TREM: Triggering receptor expressed on myeloid cells 1 synergize with TLR4

Aknowledgements Dr. Holub, M. – for her lecture material „Natural Immunity” used as source