Immunity: innate and acquired; antibodies and immune responses
Innate immunity is non-specific and present from birth; acquired immunity is pathogen-specific and has memory, using antibodies from B cells and killing by T cells.
Innate immunity: four barriers
| Barrier | Examples | How it protects |
|---|---|---|
| Physical | Skin; mucus lining the respiratory, digestive and urogenital tracts | Skin blocks entry; mucus traps microbes |
| Physiological | Acid in the stomach, saliva in the mouth, tears | Prevent microbial growth |
| Cellular | Neutrophils (PMNL), monocytes, natural killer cells in blood; macrophages in tissues | Phagocytose (engulf) and destroy microbes |
| Cytokine | Interferons secreted by virus-infected cells | Protect non-infected cells from further viral infection |
Innate vs acquired immunity
Primary vs secondary response
Antibody structure and how to draw it
- Antibodies are proteins made by B-lymphocytes (through plasma cells) in response to pathogens.
- Draw a Y shape made of four chains: two long heavy chains forming the full Y, and two short light chains along the outer side of each upper arm.
- Join the chains with short lines marked S-S (disulphide bonds): between the two heavy chains, and between each heavy and light chain.
- Label the tips of the two arms antigen binding sites. Write N at the free tips and C at the lower ends of the heavy chains, as in the textbook figure. Extra labels, not in that figure: the tips are the variable region, the rest the constant region.
- Write the formula H₂L₂ below the figure.
Humoral vs cell-mediated immunity
The acid in your stomach and the tears in your eyes are part of your innate immunity. When a relative gets a kidney transplant in an Indian hospital, doctors first match tissues and blood groups, then give lifelong immunosuppressants to stop T cells rejecting it.
2 marks: “Name the four barriers of innate immunity with one example each.” Physical: skin, mucus. Physiological: stomach acid, saliva, tears. Cellular: neutrophils, monocytes, NK cells, macrophages. Cytokine: interferons.
3 marks: “Draw a labelled diagram of an antibody molecule. Why is it written as H₂L₂?” Y-shaped with two heavy and two light chains, S-S bonds, antigen binding sites at the tips (extra labels: variable and constant regions). H₂L₂ because it has two heavy and two light chains.
3 marks: “Distinguish between humoral and cell-mediated immune responses. Why are transplanted organs sometimes rejected?” Humoral: B cells, antibodies in blood. CMI: T cells act directly. Rejection: body recognises the graft as non-self and CMI destroys it; hence tissue matching and immunosuppressants.
B cells make antiBodies (Blood, humoral); T cells do the Tough fighting (cells, transplants).