Pattern recognition or a danger response Shivers 1975 David Cronenberg What do you want your immune system to do Prevent colonization by dangerous microbes Prevent tissue overgrowth cancer Destroy infected cells Aid in wound disinfection and healing T Cell activation requires two signals Early models suggested that two signals were required to activate T cells but the antigen presenting cells were largely considered to be constitutively active Pattern recognition hypothesis Charles Janeway 1989 Proposes that APCs must be activated APCs are induced by conserved products of pathogens Suggests that there are pattern recognition receptors PRRs and pathogen associated molecular patterns PAMPs Janeway proposed there would be PRRs and PAMPS Pattern recognition receptors PRRs Pathogen associated molecular patterns PAMPs cell wall lipid What does this pattern recognition model give us Constitutive model Pattern recognition Danger hypothesis Polly Matzinger 1994 Suggested that the antigen presenting cells were activated by a danger signal from damaged tissue This model explains several issues not explained by the PRR PAMP camp Comparing the three models Constitutive Stranger Danger The guard hypothesis What is a pattern recognition receptor Phylogenetic perspectives in immunity The insect host defense 1994 Hoffmann Janeway Natori eds Pattern recognition in the horseshoe crab hemocyte Exocytosis of granules Factor C activation by LPS Coagulation induction in vitro LPS No Induction Ariki et al 2004 PNAS 101 953 958 Horseshoe crab clotting cascade glucan Factor G LPS Factor C Factor B Coagulogen Coagulation enzyme Factor C is also responsible for exocytosis of hemocyte granules Unknown protease activated receptor PAR LPS Factor C Exocytosis Signal Ariki et al 2004 PNAS 101 953 958 The Toll pathway used during embryonic development Lateral view of normal gastrulation 1st instar larval cuticles prepared from eggs layed by Toll mutant mothers Toll structure and mutant analysis Wild Type Toll Protein Class 1 mutant Class 2 mutant Leucine rich repeats Truncated extracellular domain active only in presence of upstream signal and wt allele of Toll Terminal sequence Leucine rich repeats Terminal sequence C Y Cytoplasmic domain similar to interleukin 1 receptor Constitutively active intracellular domain Schneider et al 1991 Genes and Development 5 797 807 Winans and Hashimoto 1995 Mol Biol Cell 6 587 596 Injection into the perivitelline space to identify polarizing activity Site of injection defines ventral Polarizing activity assay Cuticle Wild type Gastrulation pattern Wild type Dorsalized Dorsalized Rescued by injection Rescued by injection Rescued by injection Purification to invisibility a new standard Where s the beef Toll signaling in dorsal ventral patterning in Drosophila gd protease snk protease ea protease spz ligand Toll receptor dMyD88 tub pelle kinase Cac ikB dl NFkB dif NFkB immunity only Nucleus Effects of imd on survival of bacterial infections Lemaitre et al 1997 PNAS 94 14614 9 Antimicrobial gene synthesis is affected in imd flies Lemaitre et al 1997 PNAS 94 14614 9 Why is imd so lethal in the next paper Lemaitre et al 1997 PNAS 94 14614 9 Lemaitre et al 1996 Cell 86 973 83 Mutations in the Toll pathway block synthesis of antifungal peptides Lemaitre et al 1996 Cell 86 973 83 Toll mutant flies are very sensitive to fungal infections Lemaitre et al 1996 Cell 86 973 83 Lemaitre et al 1996 Cell 86 973 83 Identification of other genes in the pathway Genetic screens for antimicrobial gene synthesis defects genetic modifiers Cherry picking obvious genes Phagocytosis assay gd protease Fungi Gram snk protease osi GNBP seml PGRP ea protease spz ligand psh protease Toll receptor dMyD88 tub pelle kinase Cac ikB dl NFkB dif NFkB immunity only Nucleus Screening for mutants using a lacZ reporter assay Wu and Anderson 1998 Nature 392 93 7 Phagocytosis assay Monitoring loss of phagocytosis in RNAi treated cells Ramet et al 2002 Nature 416 644 8 PGRP LC RNAi blocks E coli but not S aureus phagocytosis Ramet et al 2002 Nature 416 644 8 PGRP LC mutants are sensitive to E coli infections Ramet et al 2002 Nature 416 644 8 gd protease Fungi Gram snk protease osi GNBP seml PGRP ea protease Gram spz ligand psh protease PGRP LC Toll receptor imd adaptor dFADD dMyD88 tub Dredd caspase pelle kinase Cac ikB rel NFkB dTAK To Jnk dl NFkB dif NFkB immunity only Nucleus IKK kinase complex