1. Cell:Cell Communication Cells can communicate by: Soluble factors Surface interactions Cytokines Soluble factors that bind specific receptors Influence gene expression May have pleiotropic or antagonistic effects Autocrine: self-stimulating Paracrine: stimulate adjacent cells Endocrine: interact with cells far away, usually via circulation Provide differentiation signals Provide recruitment signals Provide activation signals Involved in T and B cell collaboration

2. Cytokines were originally discovered in the 1960’s Were assessed in biologic assays Originally Named based on their biologic effects Noted in allogeneic mixed culture supernatants Interleukins- cytokines from leukocytes Now named by number IL-1….IL-30

3. Function of Cytokines Lymphocyte activation IL-1 Produced by macrophages, Dendritic cells, B cells Endogenous pyrogen Functions on T and B cells Promotes differentiation and clonal expansion Increased expression of adhesion molecules on EC IL-2 Secreted by Th1 cells Causes proliferation/growth of activated T cells NK cells Can be Autocrine

4. Macrophage Activation IL-4 Secreted by Th2 cells Increases phagocytic activity Increases MHC II expression IL-10 Secreted by TH2 cells Suppresses cytokine production Down-regulates MHC II expresssion

5. TH1 Vs TH2 Cells TH1 Inflammatory cell Activates macrophages Stimulates T cell responses Secrete: IL-2 IFN-  inhibits TH2 proliferation TNF-  activates macrophages TH2 Helper T cell Stimulates Ab production Secrete: IL-4 antagonizes IFN-  IL-10 inhibits IFN-  synthesis IL-5 stimulates B cell, eosinophil growth and differentiation

6. Disease States Associated with TH1/TH2 Responses Autoimmune Diseases Experimental allergic encephalomyelitis (EA) Inappropriate TH1 response to myelin basic protein inCNS Leprosey Dominant, inappropriate TH2 response Allergies TH2 responses, preferential production of IgE AIDS TH1 to TH2 switch associated with disease progression

7. Inflammatory Cytokines TNF-  Increases vascular permeability- heat, swelling, accumulation of Ig and complement Induces expression of adhesion molecules Recruits cells to sites of inflammation Facilitates extravasation Harmful if produced systemically (during sepsis) Increased vasopermeability causes loss of plasma volume, shock Triggers disseminated intravascular coaggulation, kidney, liver heart failure IL-8 Causes inflammation, cell migration Alters conformation of adhesion molecules on monocytes, increases affinity for ICAM-1 encourages migration through tissues

8. Chemokines Small peptides released by many cell types In response to injury As part of normal cell function (stromal elements) Cells migrate towards increasing concentration (gradient) of chemokine Must have specific receptor for chemokine Classified based on position of 2 of 4 conserved cysteins C-C chemokines have consecutive cysteins MCAF (macrophage chemotactic/activating factor RANTES (made by activated T cells, attracts memory T cells MIP-1  (attract T cells) C-X-C chemokines have another amino acid between cysteins IL-8 SDF-1 (stromal-derived factor) Several chemokines block secondary receptors for HIV SDF-1, RANTES, MIP-1  and 

9. Interferons Natural protective cytokines (innate) IFN-  produced by leukocytes in response to viral infection IFN-  produced by fibroblasts and other cell types in response to viral infection Double stranded RNA causes expression of IFN Causes activation of endoribonuclease Cleaves viral RNA Induces expression of proteins that inhibit translation Cell killed, virus replication halted IFN-  produced by activated T cells, NK cells Increases expression of MHC I and II Inhibits virus replication TH1 cytokine

10. Differentiation of Hematopoietic Cells Effects on bone marrow progenitors Erythropoietin: induces development of red blood cells M-CSF: induces formation of macrophage colonies G-CSF: induces formation of granulocyte colonies GM-CSF: induces formation of granulocyte and macrophage colonies IL-3: induces proliferation, differentiation of granulocytes and macrophages

12. SDF-1

14. Common  -chain Receptor Shared by receptors for IL-2,-4,-7,-9,-15,-21 Mutation in this gene causes inability to respond to any of these cytokines Results in x-linked severe combined immunodeficiency Cannot make B cells, T cells or NK cells This disease has been “cured” in some patients by stem cell gene therapy A second type of SCID defect can be caused by mutations in the IL-7 receptor These patients have B and NK cells, no T cells In humans, IL-7 is absolutely required for T cell development

15. Surface Interactions Function in adhesion and differentiation Surface interactions can influence adhesion Increase expression of adhesion molecules alter conformation, allow greater adhesion Extracellular matrix can trap cytokines concentrates and maintains them Glycoaminoglycans bind chemokines helps recruit cells Surface interactions induce differentiaion In thymus: Binding MHC I leads to CD8 commitment Binding MHC II leads to CD4 commitment Strong binding of TCR with MHC leads to clonal deletion of developing cells

16. Nueroendocrine Interactions Stress may correlate with susceptibility to disease Lymphocytes make about 20 neuroendocrine peptides Related cytokines and receptors found in the brain Hypothalamic-Pituitary-Adrenal axis (HPA) Hypothalamus: releases corticotropin-releasing hormone causes release of ACTH from pituitary ACTH acts on adrenal gland, produces glucocorticoids altered metabolism suppressed immune system feeds back on pituitary Neuropeptides influence lymphocyte migration Can alter chemokine receptor levels Influence cytokine production Alter function of thymic stromal elements

21. Years since MACS entry Proportion alive Proportion AIDS-free CD4 T cell level (% lymphocytes) Stress and HIV-1 disease progression: High-stress individuals have faster disease progression Stress hormone norepinephrine: Increases HIV expression Increases levels of CXCR4 (HIV co-receptor) High-stress individuals respond poorly to therapy

22. Circulation/Extravasation Granulocytes and monocytes travel exclusively in blood Lymphocytes circulate in blood and lymph Distribution of lymphocytes to tissues is not random It is controlled by specific receptors on lymphocytes and on target tissues

23. Virgin lymphocytes from blood entering into lymph node/spleen Bind molecules on post-capillary venules Squeeze between cells Now in lymph

24. Circulation of Activated T Cells From Blood 1. If cells find site of infection: Endothelial cells of capillary are altered, and now express adhesion molecules T cells bind these molecules, squeeze between endothelial cells When Ag is removed, T cells become memory cells Get swept into lymphatics, float to nearest lymph node 2. If cells do not find site of infection: Become de-activated, convert to memory phenotype Float to blood vessels in the skin Bind to adhesion molecules on post-capillary venules in skin Squeeze between endothelial cells, are swept away into lymph This distributes memory cells throughout the body

25. Summary of T Cell Movement Naïve T cells: Exit blood at post-capillary venules in nodes Activated T cells in blood : If find area of infection Bind to adhesion molecules on EC Extravasate Swept to local node after become memory cells If do not find area of infection Become de-activated memory cells Exit blood at post-capillary venules in skin Drift to nodes near that site

26. Trafficking is controlled by: Appearance/disappearance of adhesion molecules on endothelial cells Appearance/disappearance of their ligands on lymphocytes At the site of inflammation, pro-adhesion molecules induced on EC Ligands on WBCs bind, cell slows down and rolls (marginalization) This induces expression of true adhesion molecules on WBC (also EC) Additional signals Induce cells to move Towards the site of inflammation Cell extravasates