Core Concepts-L4-Inflammation and Cellular Recruitment

what is the hierarchy of cells in the inflammatory response?

1. resident cells are the first sensors- macrophages, DC, mast cells

• detect infection by pattern recognition receptors- PRR’s and release inflammatory mediators

• cytokines- IL-1, TNF, complement fragments like C3a and C5a and induce vasodilation

• 2. blood vessel respond to this- up regulate adhesion molecules like E-selectin and P-selectin. lose tight junction integrity and allow leukocytes in to deliver immune cells and humeral factors(complement, Ab)

• 3. chemokine guide trafficking. neutrophils have CXCR1 and follow CXCL8 first. monocytes have CCR2 receptors and follow MCP-1/CCL2

where do immune cells come from?

• bone marrow stem cells- self renewing pluripotent

• stroll cells support hemopoiettic stem cells

• hematopoietic stem cells give rise to all blood and immune cells and differentiate from lymphoid progenitor and myeloid progenitor(and erythrocytes)

how does hematopoiesis work?

• regulated by growth factors and cytokines- CSF-1 or GM-CSF

• lineage specific transcription factors- such as C-kit and Lineage markers

• also depends on the niches and specific environment

what do phagocytes do?

1. destroy pathogens or debris to limit infection

2. create peptide antigens for T/B cells recognition

3. signal and modulate immune responses

explain the process of phagocytosis

1. recognition- detect danger signals- PAMPs and MAMPs

2. cell membrane rearranges its actin cytoskeleton and forms a phagosome.

3. phagosome then fuses with the lysosome to form a phagolysosome. has digestive enzymes and reactive oxygen species for killing microbes.

4. NADPH oxidase on phagosome membrane produces superoxide and kills microbes

what are phagocytic cells are there?

1. macrophages- professional phagocytes- engulf microbes and debris and antigen presentation

2. neutrophils- highly antimicrobial- engulf and kill microbes and degranulate and form nets

3. dendritic cells- phagocytose microbes and present antigens to T cells- perform macropinocytosis- always taking in its environment and sampling it

role of antigen presenting cells and how do they do this?

• capture and process antigens on MHC molecules to antigen specific lymphocytes

• MHC I- endogenous/intracellular pathogens- to D8 cells

• MHC II- CD4 cells- exogenous-extracellular pathogens

steps of T/B cell activation

1. recognition- T/B cell receptor binds to the MHC

2. produce costimulatory cells from the APC- CD80

3. cytokine signalling- APC makes cytokines and helps with T cell differentiation

describe the difference between the induction vs effector phase and when does this happen

• induction phase- in the lymph nodes- naive T cells encounter antigens from APCs and get activated and differentiate

• effector phase- at the site of infection- activated T cells migrate to the infected tissue and recognise their specific antigen- and target elimination

induction- trains T cells

effector- action at the infection site

discuss resident phagocytic cells

macrophages

• more frequent than DCs and are irregular shaped.

• rich in lysosomes 

• from myeloid progenitor- common at mucosal surfaces

• has PRR’s and can present antigens

name the type of innate immune cells

1. phagocytic cells- engulfs and destroy pathogens/debris. can also signal the immune system. macrophages/neutrophils/DC

2. signalling cells- detect pathogens/danger signals and release mediators. can also recruit other immune cells. certain DCs, innate lymphoid cells, mast cells

name phagocytic surface markers

• CD11b- inter grin involved in adhesion and phagocytosis

• CD14- coreceptor for LPS recognition(TLR4)

• F4/80- classic macrophage marker found in the mouse

discuss tissue resident DC

• has CD11c integrin, CD80/86- a costimulatory molecule for T cell activation

• Has mHC antigen complexes- to present to T cells

• has CCR7- a chemokine receptor to bring it to the lymph nodes

• resident in tissues but always trafficking through lymphatics

discuss epithelial resident cells

• express pattern recognition receptors and TLRs- regulated in the gut to stop overactivation

• nn phagocytic- specialised transport for nutrient absorption but traffic molecules like innate cells

• uses xenophagy to restrict infection- degrades damaged organelles in a double membrane vesicle. acidifies vesicle and fuses with lysosome to control cytoplasmic infection

discuss intestinal epithelial cells

• IeCs- mucosal surface- senses via PRRs and degrades damaged organelles and cytoplasmic pathogens

• paneth cells- small cells- produce AMPs

• goblet cells- among epithelium- make mucin and forms a protective mucosal barrier

• M-cells- transports antigens via transcytosis- deliver to underlying APCs

discuss mast resident cells

• degranulates

• releases histamine and other mediators

• causes vasodilation and fluid release and stimulates local nerves, recruits immune cells to sites of inflammation

discuss specificity in immune cell recruitment

chemokine and ligands

• CCL2 target monocytes via CCR2- follows chemokine gradient to site of infection

• CCL21- lymphocytes- guides migration to lymph nodes for APC

• neutrophils- CXCL8(IL-8) is produced and has CXCR1 detect gradient

discuss neutrophil recruitment

• rolling: neutrophils slow down in the bloodstream near site of infection

• selectin on activated endothelial cells- E-selectin/P-selectin are upregulated on inflamed endothelium and binds to carbohydrate ligands on neutrophils. stops neutrophils from flowing freely and ROLL instead

• chemokine released from the tissue bind to chemokine receptors on neutrophils- CXCL8 binds to receptor CXCR1/CXCR2. activates intergrins(LFA-1/Mac-1)on neutrophils for firm adhesion

• adhesion- integrins(LFA-1/Mac-1)- bind tightly to immoglobulin superfamily adhesion molecules on endothelial cells- ICAM-1 and ICAM-2. goes from rolling to firm arrest at site of inflammation

discuss macrophage recruitment

• monocytes- rolling and have loose interaction due to up regulation of selecting on activated endothelium slow down monocytes.

• P selection and E selection on endothelium cells and monocyte P selection glycoprotein ligand 1 on the monocytes. binding occurs via carbohydrate monomers

• chemokine from tissue bind to monocyte receptors CCL2 to CCR2 receptors- activates integrins for firm adhesion

• Ig superfamily on endothelium interact with integrins on monocytes. ICAM-1(on endothelium) and VACM interact with mCR3 on the monocyte

• MCP-1 and CCR-2 chemokine help the monocyte get under the endothelium 

discuss macrophage differentiation

1. monocyte integrins CR3 are activated during firm adhesion which rearranged the actin cytoskeleton to allow the monocyte into the endothelial cells- DIAPEDESIS

2. once in the tissue- monocytes find the chemokine CCL2(CCR2 receptor)

3. maturation- entry into tissues triggers maturation. key signal CSF-1 promotes the phagocytic capacity and survival. makes large cytoplasm with lysosomes and the ability to secrete cytokines

4. become M1 macrophages by IFN-gamma, TNF- pro inflammatory or M2 macrophages- IL-4, IL-13 by dead cells and are anti inflammatory and secrete IL-10

difference between immune cell infilitration- neutrophils vs monocytes

• timing- neutrophils are recruited first

• chemokine in monocytes- CCL1 and responds by CCR2 receptor in monocytes

• chemokine in neutrophils- CXCL8 responds by CCL2 in neutrophils.

• integrins in neutrophils- LFA-1,Mac-1

• integrins in monocytes- CR3/Mac-3

discuss similarities between cell infiltration between neutrophils and monocytes

• rolling/firm adhesion/diapedesis

• both depend on chemokine gradients(nt- CXCL8-CCL2, mono-CCL1 responds by CCR2)

• interaction with firm adhesion- both use selectin P/E and integrins for firm adhesion- ICAM-1, VCAM-1