Chapter 11: Immunity in Humans

11.1 Body Defence

• A pathogen is a microorganism that causes disease (bacteria, viruses, parasites). (p.200)
• Antigens are foreign particles that stimulate an immune response; antibodies are proteins produced by lymphocytes that destroy antigens. (p.200)
• Immunity is the body's ability to fight infection through specific attacks on pathogens. (p.200)
• First line of defence (non-specific): physical and chemical barriers that prevent pathogen entry. (p.200)
• Skin: tough physical barrier; shedding dead cells; sebum (oil and acid) and sweat lysozyme act as a chemical shield. (p.201)
• Mucous membranes trap microbes; lysozyme in tears, nasal mucus and saliva destroys bacteria; stomach HCl destroys bacteria; blood clotting seals wounds. (p.201)
• Second line of defence (non-specific): fever, inflammation, phagocytosis. (p.202)
• Fever increases phagocytic activity and fights infection. (p.202)
• Phagocytes (neutrophils, monocytes) engulf pathogens; lysosome lysozyme digests them in the phagolysosome. (p.202)
• Inflammation: damaged tissue releases histamine, capillaries dilate and become more permeable, phagocytes and clotting factors gather at the site (redness, swelling, pain). (p.203)
• Pus is microorganisms, tissue fragments and white blood cells. (p.203)
• Third line of defence (specific): lymphocytes produce antibodies; T lymphocytes attack infected cells and stimulate B lymphocytes to produce memory cells. (p.203)
• Memory cells produce antibodies immediately if the same pathogen returns. (p.203)

11.2 Actions of Antibodies

• Neutralisation: antibodies bind toxins from bacteria. Agglutination: pathogens clump together. Precipitation: dissolved antigens form insoluble complexes. (p.204)
• Opsonisation: antibodies mark antigens for phagocytes. Lysis: antibodies cause bacteria to break down. (p.205)

11.3 Types of Immunity

• Active immunity: lymphocytes produce their own antibodies. Passive immunity: antibodies come from an external source. (p.205)
• Natural active: after recovering from infection. Artificial active: vaccine injection. Natural passive: from mother through placenta and breast milk (colostrum). Artificial passive: antiserum injection. (p.205)
• Vaccine is a suspension of weakened, dead or non-virulent pathogens; a booster dose raises antibodies above the immunity level. (p.206)
• Examples: Salk vaccine (polio), BCG (tuberculosis), HPV vaccine (cervical cancer). (p.206)
• Antiserum (e.g. antitetanus, anti-rabies, snake antiserum) gives immediate but short-term protection. (p.207)

Artificial active vs artificial passive immunity

(p.208)

Aspect	Artificial active	Artificial passive
Injected	Vaccine	Antiserum with antibodies
Purpose	Prevention	Treatment or immediate protection
Protection	Not immediate, long lasting	Immediate, temporary
Antibodies from	Own lymphocytes	Antiserum

11.4 Health Issues Related to Immunity

• HIV attacks lymphocytes and causes AIDS, progressively destroying the immune system. (p.209)
• Symptoms appear after 8 to 10 years; patient dies from other infections. (p.209)
• HIV spreads through blood, semen, across the placenta, during birth and breastfeeding; also sharing contaminated needles. (p.209)
• HIV mutates, giving high resistance to drug therapy. (p.209)
• Research topics: Systemic Lupus Erythematosus (SLE) and allergy. (p.210)