unit 4- lesson 3, Innate Immunity: Cells, Molecules & Complement System

• Lesson 3 focuses on innate immunity including cells, molecules, and the complement system.
• The case scenario describes a 53-year-old woman diagnosed with Rheumatoid arthritis about 7 years ago and is now prescribed Adalimumab, a TNF alpha inhibitor.
• The lesson goes on to discuss immune cells and TNF involvement in inflammation, contra-indications, and cautions.
• Ellie asks about cells taking place in the innate immune system.
• Ellie asks about the importance and role of TNF-a in inflammation.

Cells in Innate Immunity

• Key innate immune cells are Neutrophils, Monocytes, Macrophages, Natural Killer cells, and Mast cells.
• The humoral aspect of the innate immune system involves the Complement system.
• B and T cells are part of the adaptive immune system.
• Macrophages and Neutrophils are phagocytes.
• Macrophage activation happens due to cytokine release.
• Neutrophils are first responders and engulf and destroy pathogens
• Macrophages are involved in phagocytosis, antigen presentation, and cytokine release.
• Dendritic Cells (DCs) are antigen-presenting cells (APCs) that activate T cells, they reside in tissues exposed to the environment.
• Natural Killer (NK) Cells kill virus-infected and cancer cells and are found in the blood and tissues.
• Mast Cells release histamine, trigger inflammation, and are involved in allergies and are in the tissues

Monocytes and Macrophages

• Monocytes arise from a myeloid precursor and circulate in the blood.
• Monocytes differentiate into macrophages when they leave the circulation and go into different tissues.
• Macrophage populations are heterogenous, requiring specialization tailored to their location.
• Detection, phagocytosis, and destruction of bacteria and harmful organisms occur within macrophages.
• Macrophages produce reactive oxygen species like nitric oxide to eliminate phagocytosed bacteria.
• Toll-like receptors (TLRs) are used by macrophages and bind pathogen components like LPS, RNA, DNA, or extracellular proteins.
• Macrophages present antigens to T cells.
• ROS and RNS are produced when macrophages kill intracellular bacteria.
• A cytokine that enhances bacterial killing activates the ROS and RNS pathways.
• Macrophages migrate and circulate within many tissues to eliminate dead cells or patrol for pathogens.
• Alveolar Macrophages in lung alveoli conduct phagocytosis and control immunity to respiratory pathogens.
• Kupffer cells in the liver initiate immune responses and hepatic tissue remodelling.
• Microglia in the central nervous system eliminate old neurons and control immunity in the brain.

Macrophage Communication

• Macrophages interact with their environment thru membrane receptors like B cell/Antibody IgG, TLR receptor, Complement C3b receptor.
• Macrophage surface receptors also support antigen presentation (MHCII) and response to cytokines (TNF-a etc).
• Cell-cell adhesion receptors(integrins) support cell adhesion and TNF-a production.
• Toll-like receptors (TLRs) are pattern recognition receptors that bind PAMPs (pathogen-associated molecular patterns).

Macrophages and Disease

• Key Message: Macrophages display significant functional heterogeneity and are distributed throughout the tissues.
• Macrophages acquire pro- or anti-inflammatory functions influenced by cytokines and the tissue's microenvironment.
• In inflammation, macrophages execute antigen presentation, phagocytosis, and immunomodulation via cytokines and growth factors.
• Resolution of inflammation is critical, inflammation leads to disease.
• Macrophages orchestrate many diseases like sepsis, infection, chronic inflammatory diseases, neurodegenerative diseases and cancer.
• Drugs may block inflammatory mediators that are released from macrophages.

In Rheumatoid Arthritis (RA)

• Macrophages contribute to the pathogenesis of RA.
• Rheumatoid arthritis is an autoimmune and inflammatory disease of the joints.
• Macrophages produce pro-inflammatory cytokines and chemokines, releasing cytokines (IL-1, IL-6, TNFa, IL-8) to activate other cells.
• Macrophages also contribute to cartilage and bone destruction in RA.
• Macrophages can cause chronic inflammatory and autoimmune diseases like rheumatoid arthritis.
• Macrophages and epithelial cells release chemokines such as CXCL8 (IL-8) to attract neutrophils.
• Macrophages and neutrophils mediate inflammation and tissue damage.
• Chemotherapy-induced mucositis is made worse by their activation.
• TNF-a promotes inflammation by increasing immune cell recruitment and vascular permeability and blocking this reduces joint inflammation.
• Risks: TNF-a inhibitors increase susceptibility to infections like tuberculosis.
• Macrophages failing to clear pathogens cause chronic disease.

Neutrophils

• They are also known as polymorphonuclear neutrophils(PMNs).
• They are the most abundant white blood cell in the blood.
• The multi-lobed shape of their nucleus distinguishes them from other white blood cells.
• Neutrophils are first responders at sites of acute inflammation to chemotactic cues such as CXCL8.
• Neutrophils defend against invading microbes by phagocytosis and/or releasing antimicrobial factors.
• Direct interaction w/pathogens thru PAMPs(pathogen-associated molecular patterns) by recognition receptors occurs.
• Indirect interaction - thru recognition of antibody-opsonised microbes via Fc receptors or complement opsonin receptors.
• The phagosome undergoes maturation and fusion with neutrophil granules and delivery of antimicrobial molecules and generation of ROS.
• Degranulation of specific granules on the neutrophil surface and extrusion of nucleic acids form antimicrobial NETs.
• NETs create an antimicrobial milieu at the inflammatory site inhibiting pathogens.
• Degranulation is a cellular process releasing cytotoxic molecules from secretory vesicles.

Neutrophils and Disease

• Chronic Granulomatous Disease is a genetic disorder characterized by recurrent bacterial/fungal infections.
• A defect in phagocytes - neutrophil causes this.
• There is an absence of phagocytosing function, therefore pneumonia and abscesses of the skin, tissues, and organs occur.
• Treatment includes antibiotics, Immunomodulation, and Hematopoietic stem cell transplantation

Case Scenario

• A 65-year-old man (Neville) underwent chemotherapy and has drug-induced neutropenia.
• Infections can occur as a complication of neutropenia.
• Mucous membranes such as the inside of the mouth and the skin are affected most often.
• Ulcers and abscesses are apparent if one has these infections.
• Neutropenia is caused by decreased production or increased destruction of neutrophils.
• Decreased production results from suppressive chemotherapeutic drugs of bone marrow myeloid progenitor cells.
• Other causes are blood and bone marrow disorders or deficiencies in vitamins or minerals.
• Infections are a complication of neutropenia because neutrophils are the defense against extracellular pathogens.
• The treatment is antibiotics and Filgrastim which is a blood growth factor that stimulates bone marrow to produce infection fighters.

Dendritic Cells

• DC precursors migrate from bone marrow into non-lymphoid tissue, and reside in an immature state (iDC).
• They sample their environment continuously by endocytosis, macropinocytosis and phagocytosis.
• DCs are present in tissues contacting the external environment like the skin, nose, lungs, stomach, and intestines.
• Dendritic cells (DCs) are responsible for initiating adaptive immune responses and function as ‘sentinels.’
• A high surface area permits contact with other cells like T cells, NK cells, and neutrophils.
• Resident DCs detect intruders by pattern recognition receptors, capture antigens, and migrate.
• They move to the T-cell zones in the draining lymph nodes to activate T-cells.

Dendritic Cells and Disease

• Exploiting the immune-regulatory capabilities of DCs is promising for treating autoimmune diseases, cancer, and transplant rejection
• Tumours suppress DCs by secreting anti-inflammatory cytokines such as IL-10.
• This downregulates tumour-killing T cells.
• DCs are used to stimulate the immune system in DC immunotherapy.
• DCs are generated and loaded with antigens in vitro to re-inject and boost the host's immunity.
• DC vaccines generated in this way are generally safe and effective.
• Tumors suppress DCs to escape immune detection and DC Vaccines help reactivate the immune repsonse.

Natural Killer (NK) Cells and Mast Cells

Components of Innate and Adaptive Immune System

• Innate immunity is the first line of defense, providing immediate, non-specific immune responses through phagocytosis, cytokine secretion, and antigen presentation.
• Main Innate immune system components include:Neutrophils, Macrophages, and Dendritic Cells

Cell Types, Function, and Relevance

• Neutrophils' main function is Phagocytosis, ROS-mediated killing, and NET formation and when defective will show Neutropenia, and Chronic Granulomatous Disease
• Macrophages present the antigen, use inflammatory cytokine production, and promote tissue repair, defects will affect Rheumatoid Arthritis and Sepsis
• Dendritic Cells are Antigen-presenting cells (APCs) which stimulate T=cell activation and defects will affect immune invasion and autoimmunity

Key Summary of Systems

• These cells patrol tissues, identify pathogens or damaged cells, and trigger release of cytokines and chemokines.

The Complement System

• Complement is an innate and humoral immune response.
• Key proteins are present in the circulation but does not describe cellular components.
• Complement is a defence mechanism and part of the innate immune response in the blood.
• The humoral component of innate immunity, a non-cellular defence, but acts in the blood by proteins made by the liver.
• Complement is activated in response to pathogens.
• Consists of about 40 plasma proteins and is rapidly amplified by small triggers.
• The cascade is tightly activated by soluble and membrane-associated proteins.
• The immune cells express and respond to complement proteins.
• It is instantly activated in response to pathogens through pattern-recognition receptors.
• Proteolytic cascade, serine proteases and Many are zymogens.

Types of Pathways

• Alternative, Classical and Lectin:
• They function by forming lytic protein complexes to lyse invading bacterial cells in the vascular.
• "Tickover" allows for low level activation and rapid, powerful response to pathogens.
• Cascade allows AMPLIFICATION of response when enzyme is activated one step generates molecules at the subsequent step.

Three Complement Activation Pathways

• The complement system consists of about 40 plasma proteins that are activated continuously but regulated.
• Direct recognition by microbes is part of the Alternative Pathway via C3B or Facto D, the process dies not require antibodies
• Mannose bacterial sugars (e.g. , C1q, C1 r, C1s, C2, C are part of the Lectin pathway and Recognizes bacterial surfaces
• Antibody Antigen complexes are part of the classical pathway

Complement and Cellular Recognition

• The Antibodies binds pathogen surface this antibody antigen recognized by complementing 1 complex
• C1 complex is molecular complex made up of 1x C1Q 2XC 1r 2x c1c
• This pathway needed for activation generate antibodies, antibody alone or antigen not detected

Activating The Alternative Pathway (Amplification and Regulation)

• Alternative pathway is constantly being ticking over at low levell allows for repulsively.
• Presence of LCS bacterial the way by bonding components
• C3 occurs when upon hydrolysis product is ch2 ho
• Factors are the convertase which C3b and C3a.

Function of the Complement System (Enhance the Immune System)

• Direct killing bacteria and affecting cells MAC (membrane attack complex)
• Cell activation like increased response
• B cell activation and adaptive community
• Initiation or the chance of inflammation.

Three Biological Fuctions

• Optamination if microorganism binds like and protein cell in microbes
• 3a c35a release and activating cells is cell lysis membrane

Initiation and Breakdown

• Complement starts with one of the three pathways and the enzyme cleaves C3 to form C3A and C3B
• The three pathways are a function.
• Regulation stops excessive alternative pathway the most abundant of cascade cell.
• There factor mutation uncontrolled
• c58-9 Complex infection C59 is of a breakdown of cells 3,5

Regulation In The Alternative Pathway

• Amplification loop has constant C5C3 molecules
• Is how to defend attack of community

Complement System Deficiencies

• Can lead to reoccuring bacterial factors
• They are activated by deficiency and it leads to red blood cells destruction by comment cell C3b
• Soliris prevents forming of the MAC membrane