Adaptive

Question 1

🛡️ 1. Which barriers constitute the major defence against pathogenic organisms?

Answer 1

Physical barriers (1st line of defense):

Skin – tough, dry, keratinized, sheds microbes

Mucosal surfaces – tight junctions + mucus trap microbes

Cilia – in respiratory tract, push out trapped particles

Chemical barriers:

Low pH (e.g., stomach acid)

Enzymes – lysozyme (tears/saliva), defensins (gut, skin)

Surfactants – disrupt microbial membranes

Microbiological barrier:

Commensal microbiota – outcompete pathogens

Question 2

What are the elements which protect these barriers?

Answer 2

Mucus (goblet cells)

Tight junctions (epithelial cells)

Antimicrobial peptides (defensins, cathelicidins)

Secretory IgA (neutralizes pathogens at mucosal surfaces)

Resident immune cells (e.g., intraepithelial lymphocytes, tissue-resident macrophages)

Question 3

Phagocytic mechanisms of deactivating microbes

Answer 3

Recognition → via PRRs or opsonins (like C3b, IgG)

Engulfment → microbe enclosed in phagosome

Fusion → phagosome + lysosome = phagolysosome

Killing:

1) O₂-independent: lysosomal enzymes (proteases, defensins)

2) O₂-dependent (oxidative burst): ROS, RNS (HOCl, H₂O₂, NO)

Question 4

Cytolytic mechanisms of deactivating microbes

Answer 4

NK cells & CD8⁺ T cells kill infected cells via:

1) Perforin → forms pores

2) Granzymes → enter through pores → induce apoptosis

3) Fas-FasL interaction → triggers cell death via caspases

Question 5

cytkines source and action

Answer 5

Cytokines Macrophages, DCs, T cells Inflammation, activation

Question 6

chemokines source and action

Answer 6

Many cells Cell recruitment

Question 7

antitbodies source and action

Answer 7

Plasma cells Neutralization, opsonization, ADCC

Question 8

complement source and action

Answer 8

Liver Opsonization, lysis, inflammation

Question 9

Complement system and mechanisms of action

Answer 9

Three pathways:

Classical: IgG/IgM + C1

Alternative: spontaneous C3b + pathogen

Lectin: MBL binds sugars → MASPs activate C4/C2

Results:

C3b → opsonization

C5a/C3a → chemotaxis/inflammation

C5b-9 (MAC) → lysis

Question 10

Antibody Function IgG

Answer 10

IgG Opsonization, crosses placenta, most abundant

Question 11

Antibody Function IgA

Answer 11

IgA Mucosal protection (secretory), found in saliva, tears

Question 12

Antibody Function IgM

Answer 12

IgM First produced, great at activating complement

Question 13

Antibody Function IgE

Answer 13

IgE Allergies, parasitic worms, activates mast cells

Question 14

Antibody Function IgD

Answer 14

IgD Mainly on naive B cells (function unclear)

Question 15

Innate ‘sensing’ mechanisms
Pattern Recognition Receptors (PRRs)

Answer 15

on innate immune cells detect PAMPs and DAMPs.

TLRs (surface/endosomal): detect LPS, viral RNA, DNA

NLRs: detect intracellular bacteria

RLRs: detect viral RNA

Activation leads to cytokine production, inflammation, and DC activation

Question 16

cDC function

Answer 16

Conventional DC (cDC) Antigen presentation to naive T cells

Question 17

pDC function

Answer 17

Plasmacytoid DC (pDC) Secretes IFN-α/β in viral infections

Question 18

inflammatory DC

Answer 18

Inflammatory DC Monocyte-derived in inflammation

Question 19

langerhans cells

Answer 19

Langerhans cells Skin-resident DCs