W1 Sem - Immune Cell Revision

What is the normal range of total white blood cells (WBCs) in human blood?

5,000 – 10,000 cells/µL of blood

What is the mnemonic for the relative relative abundance of leukocytes in peripheral blood?

Never Let Monkeys Eat Bananas

• Neutrophils (~60%)

• Lymphocytes (~30%)

• Monocytes (~6%)

• Eosinophils (~3%)

• Basophils (~1%)

What are the key features and functions of Neutrophils?

• Abundance: Most abundant WBC (60–70% of blood leukocytes).

• Production: Up to 10¹¹ produced daily; short-lived.

• Function: Phagocytosis, release of bactericidal enzymes (lysozyme, proteases, peroxidases), and formation of NETs (Neutrophil Extracellular Traps).

What are the primary functions and granule contents of Eosinophils?

• Functions: Kills antibody-coated parasites, modulates tissue repair, and induces inflammation (e.g., chronic asthma).

• Granule Contents: Histamine, peroxidase, lipases.

• Abundance: 1–5% of peripheral WBCs.

What are the primary functions and granule contents of Basophils?

• Functions: Fights parasites (helminths), prevents unwanted blood clots, and binds IgE to trigger allergic reactions.

• Granule Contents: Histamine, heparin, proteolytic enzymes.

• Abundance: Least common WBC (0.1–0.3%)

Match the tissue-specialised macrophage to its location:

• Liver

• Lung

• CNS

• Bone

• Liver → Kupffer cells

• Lung → Alveolar macrophages

• CNS → Microglial cells

• Bone → Osteoclasts

What are the main functions of Macrophages?

• Phagocytosis

• Killing pathogens via antimicrobial mediators

• Producing inflammatory cytokines/chemokines to recruit cells

• Presenting antigens to T cells

What is the primary role of Dendritic Cells (DCs)?

DCs are professional antigen-presenting cells (APCs) that take up, process, and present peptide antigens on MHC molecules to naïve T cells. They also produce cytokines like IL-12

Identify the major surface Pattern Recognition Receptors (TLRs)

• TLR1/TLR2

• TLR2/TLR6

• TLR4

• TLR5

What are the ligands of the major surface Pattern Recognition Receptors (TLRs)

• TLR1/TLR2: Triacyl lipoprotein

• TLR2/TLR6: Diacyl lipoprotein

• TLR4: Lipopolysaccharide (LPS)

• TLR5: Flagellin

What ligands are recognised by the endolysosomal TLRs (TLR7, TLR8, TLR9)?

• TLR7 & TLR8: Single-stranded RNA (ssRNA)

• TLR9: CpG DNA and mitochondrial DNA

What stimuli induce M1 Macrophages, and what is their role?

• Stimuli: IFN-gamma, LPS

• Key Factors Released: iNOS, TNF-alpha, IL-1, IL-6, IL-12, IL-23, MCP-1, IFN-gammatumour

• Function: Pro-inflammatory; involved in pathogen killing, tumour resistance, and graft rejection.

What stimuli induce M2 Macrophages, and what is their role?

• Stimuli: IL-4, IL-13

• Key Factors Released: IL-10, Arginase-1, CD206, CD204, TGF-beta1, VEGF

• Function: Anti-inflammatory; involved in immunoregulation, matrix deposition, tissue remodeling, and graft acceptance

Which MHC class interacts with CD4+ vs CD8+ T cells, and where are they expressed?

• CD8+ Cytotoxic T cells: Recognize peptides on MHC Class I (found on all nucleated cells).

• CD4+ Helper T cells: Recognize peptides on MHC Class II (found on APCs: DCs, Macrophages, B cells)

What cytokine polarises Th1 cells, what transcription factor is involved, and what is their main function?

• Polarizing Cytokine: IL-12

• Transcription Factor: STAT4 / T-bet

• Effector Cytokine: IFN-gamma

• Function: Cellular immunity and clearance of intracellular pathogens.

What cytokine polarises Th2 cells, what transcription factor is involved, and what is their main function?

• Polarising Cytokine: IL-4

• Transcription Factor: STAT6 / GATA3

• Effector Cytokines: IL-4, IL-5, IL-13

• Function: Humoral immunity, clearance of extracellular pathogens, and allergic responses

What are Th cells?

Th cells (or T helper cells) are a specialised subset of CD4+ T lymphocytes that play a central role in coordinating adaptive immune responses.

Rather than directly killing infected cells themselves, they act as the "conductors" of the immune system by producing specific chemical signals (cytokines) that direct, activate, and modulate other immune cells (like B cells, macrophages, and CD8+ cytotoxic T cells)

What is T helper cell polarisation

The process by which a naive CD4+ T cell differentiates into a specialised functional subset

• like Th1, Th2, Th17

• based on environmental cytokine signals

What cytokines polarise Th17 cells, what transcription factor is involved, and what is their main function?

• Polarizing Cytokines: IL-6, IL-21, IL-23, TGF-beta

• Transcription Factor: STAT3 / RORgammat

• Effector Cytokines: IL-17, IL-17F, IL-22

• Function: Tissue inflammation, clearance of extracellular pathogens, and autoimmunity

What cytokines polarize Treg cells, what transcription factor is involved, and what is their main function?

• Polarizing Cytokines: IL-2, TGF-beta

• Transcription Factor: STAT5 / FOXP3

• Effector Cytokines: IL-10, TGF-beta1

• Function: Immune suppression and self-tolerance

What are the three broad components of humoral immunity, and which are innate vs adaptive?

• Antibodies: Adaptive immune system

• Complement System: Innate immune system

• C-Reactive Protein (CRP): Innate immune system

What are the primary functions and characteristics of IgG?

Critical roles in opsonisation and neutralisation; has 4 subclasses (IgG1, IgG2, IgG3, IgG4).

What is opsonisation?

An immune process where pathogens or dead cells are coated with special proteins called opsonins (such as antibodies or complement proteins).

This tagging makes the target "tasty", helping immune cells called phagocytes easily find, stick to, and swallow the invaders

What antibody isotype is produced first during an infection?

IgM (increases transiently upon initial exposure/activation)

What are the key features of IgA?

Expressed in mucosal tissues, critical for mucosal immunity, and forms dimers after secretion.

What antibody isotype mediates allergic reactions and anti-parasitic responses?

IgE

What triggers the three pathways of the Complement System?

• Classical Pathway: Antigen-antibody immune complexes (C1q).

• Lectin Pathway: PAMP recognition by lectins (MBL binding carbohydrates).

• Alternative Pathway: Spontaneous hydrolysis / pathogenic surfaces.

What are the three primary functional outcomes of the complement cascade?

• Inflammation: Triggered by anaphylatoxins (C3a, C4a, C5a).

• Opsonization: Mediated by C3b (promotes phagocytosis).

• Cell Lysis: Formed by the Membrane Attack Complex (MAC: C5b–C9)

What are complement proteins?

A group of over 30 soluble plasma proteins (mostly synthesised in the liver) that circulate as inactivate precursors and play a critical role in innate humoural immunity by promoting inflammation, opsonisation, and pathogen lysis

• Cx

What are the four major categories of pathogens presented in Immunology?

• Viruses (e.g., HIV)

• Bacteria (e.g., E. coli)

• Fungi (e.g., Candida)

• Parasites (e.g., Malaria)

What are the body's primary physical barriers, and what process allows neutrophils to move from blood capillaries into tissue?

• Physical Barriers: Skin, mucous membranes, and associated secretions.

• Cell Migration Process: Extravasation (prompted by capillary dilation and increased permeability caused by histamine release from mast cells).

Compare the general response timelines for Innate vs. Adaptive immunity upon pathogen entry.

• Innate Immunity: Responds within minutes to hours (includes humoral factors like complement/CRP and cellular factors like phagocytes/NK cells).

• Adaptive Immunity: Takes days to weeks to develop (involves antigen presentation, CD4+/CD8+ T cells, B cells/antibodies, and memory formation)

What is C-Reactive Protein (CRP), and what part of the immune system does it belong to?

CRP is an acute-phase protein produced during inflammation. It acts as a soluble factor in innate humoral immunity.

What is the primary function of IgD antibodies?

IgD acts as a B cell receptor on naive B cells and plays a role in mucosal immunity and immune tolerance.