The human body has various defense mechanisms to protect itself from infection.
The table below lists several cells, structures, and molecules involved in the human immune response.
| Letter | Cell, structure, or molecule |
|---|---|
| A | Cytotoxic T-cells |
| B | Hydrochloric acid |
| C | Plasma cells |
| D | Interleukins |
| E | Epidermal skin layer |
| F | Opsonins |
| G | Neutrophils |
| H | Sebum |
(i) Which letter or letters indicate structures or secretions that act as primary defenses to prevent the entry of pathogens into body tissues? (ii) Which letter or letters indicate cells capable of performing phagocytosis? (iii) Which letter or letters indicate molecules that specifically bind to pathogens to mark them for destruction or enhance phagocytosis?
During an immune response, activated T-helper cells release interleukins, and virus-infected host cells release interferons. State the role of each of these molecules:
An infant is given the MMR (measles, mumps, and rubella) vaccine containing weakened (attenuated) pathogens to stimulate an immune response. (i) Which type of immunity is functioning after the infant receives this vaccine? Select from: natural active, natural passive, artificial active, or artificial passive. (ii) Explain your answer to part (i).
