Grading: Two midterm exams each worth 100 points One final worth 150 points The homework grade (100 points total) will be automatically substituted for your lowest midterm! However, you must take both midterms. If you have a valid excuse to miss a midterm (e.g., death in family, severe illness, car accident on the way to school), drop off a note signed by a relevant official to Mandy Butler’s Office, York In that case, your homework will substitute for the missing midterm. Do not miss a midterm without a valid excuse. There will be no make-up midterms. You must take the final. If you have a conflict with the Final date, let me know immediately.

Lecture 3 Innate immunity and leukocyte migration Relationship between plant immunity and vertebrate immunity NODs RNA interference by small interfering RNAs Quick review- complement and its subversion phagocytosis Leukocyte migration/extravasation Lymphocyte recirculation Distinction between spleen and lymph nodes Next lecture: antibodies (Reading Parham, Chapters 2 and 7)

Seen by Tlr2 (cell surface receptor) Lysozyme (in serum and secretions) clips here Numerous innate sensors of bacterial peptidoglycan Mammalian NOD1 and NOD2 (intracytoplasmic sensors)

NOD signaling activates NFkB transcription factor Peptidoglycan

NOD domain proteins are conserved between humans and plants (they also are related to Toll like receptors [Tlrs]) * * In plants R proteins confer resistance to pathogens Humans carrying NOD2 mutations develop Crohn's disease (Inflammatory bowel disease)

Lecellier, Charles-Henri & Voinnet, Olivier (2004) RNA silencing: no mercy for viruses?. Immunological Reviews 21-25bp dsRNAs RNA interference as a widespread immune mechanism Discovered in plants dsRNA leads to dsRNA degradation in infected cell, but also sequence-specific resistance by nearby cells How can a long lived organism like a tree survive without adaptive immunity?

The short dsRNAs serve as templates to direct destruction of other mRNAs Lecellier et al. 2004

Transmission of siRNAs from cell to cell in plants Lecellier et al. 2004

Concepts The multilayered nature of immunity is a general phenomenon. RNAi is a novel type of host defense. (While RNAi is not believed to be a major defense mechanism in mammals, it is operational, and can be harnessed, for example in gene therapy.) The NOD pathway shows that even the loss of a single aspect of innate immunity can have disastrous consequences for the host. (Conserved genes are conserved for a reason, they provide fitness).

Animations Complement Phagocytosis

Virus subversion Herpes simplex Strategy 1. Hiding in immunologically priviledged sites. Fig 9.4

From Judson et al J. Virol 2003 Viral envelope proteins gC and gD are important for infection gE and also gC subvert the host response by suppressing antibody and complement mediated lysis Strategy 2. Suppress antibody and complement mediated defense mechanisms.

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Animations Leukocyte rolling Leukocyte extravasation Lymphocyte homing Chemotaxis

Langerhans' cell is a skin dendritic cell They migrate to the draining lymph node and present antigen to T cells.

A microbe- activated dendritic cell migrating to the draining lymph node through the lymphatics

Principal lymphoid organs Figure 1.8

Tissue-LN connection flow Eventually flows to thoracic duct, then back to blood

Lymph nodes drain the connective tissues of the body Figure 1.10 The segregation of different cell types within lymph nodes is controlled by chemokines and adhesion molecules.

Lymphocyte circulation Figure 1.9

The spleen drains the blood Lymphoid cells tend to congregate in discreet regions Figure 1.11

Spleen II

Morphology of the spleen

GALT-gut- associated lymphoid tissue Figure 1.12

Figure 2-13 Salmonella winkling their way in through M cells

Mucosal Immune System

T lymphocyte recirculation Bone marrow to blood Blood to thymus (Differentiation and Selection Occurs) Thymus to lymph nodes and spleen Lymph nodes to efferent lymphatics To thoracic duct emptying into the left subclavian vein Blood to site of inflammation-extravasation Tissues to afferent lymphatics To draining lymph nodes development

Movie Lymphocyte trafficking

Summary of Concepts discussed 1) Leukocyte movement is rapid and directed. Tissue damage, microbial motifs stimulate cell migration through selectin upregulation, chemokine expression, and cell adhesion. 2) Lymphoid tissue is organized. Chemokines expressed by fixed and motile cells in lymph node and spleen are important in organizing lymphoid architecture. 3) Different secondary lymphoid organs sample distinct compartments Lymph nodes Peyer's patches Spleen 4) Complement cascade is complicated 5) Even plants share some immune mechanisms with us (NODs, RNAi) Next time: antibodies (Reading Parham, Chapters 2 and 7)

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