T-lymphocytes are produced in bone marrow and mature in the thymus gland.
When mature, T-lymphocytes leave the thymus gland to travel throughout the body. They remain inactive inside organs, such as the spleen and lymph nodes, until activated by the presence of antigens.
Fig. 5.1 shows what happens to two inactive T-lymphocytes, U1 and V1, in the presence of an antigen from a virus.
(a) (i) U4 and V4 are types of active T-lymphocyte. State the names given to these types of T-lymphocyte.
(ii) Describe the roles of cells U4 and V4 in a primary immune response.
(b) Polio is a highly infectious viral disease. The virus infects the nervous system of humans. The disease can cause total paralysis within hours and can be fatal.
The Global Polio Eradication Initiative (GPEI) was started in 1988 by the World Health Organization. In 2022, polio had been successfully eradicated from most of the world. However, cases of the disease have been recorded in some countries.
Discuss the steps that must be taken by health authorities during a vaccination programme if an infectious disease, such as polio, is to be eradicated from the whole world.
▶️ Answer/Explanation
(a) (i) U4 – T-helper (lymphocyte/cell) AND V4 – T-killer/T-cytotoxic (lymphocyte/cell)
Explanation: In the immune system, there are different types of T-lymphocytes that perform specialized functions. U4 represents T-helper cells which coordinate the immune response, while V4 represents T-killer (cytotoxic) cells which directly attack and destroy infected cells.
(a) (ii)
Roles of U4 (T-helper cells):
- Secrete cytokines (cell signaling molecules like interleukins) that stimulate other immune cells
- Activate B-lymphocytes to divide and develop into plasma cells that produce antibodies
- Stimulate macrophages to become more active in phagocytosis (engulfing pathogens)
- Help coordinate both humoral (antibody-mediated) and cell-mediated immune responses
Roles of V4 (T-killer/cytotoxic cells):
- Directly kill virus-infected cells by releasing toxic chemicals
- Produce perforin which creates pores in infected cell membranes
- Release granzymes (proteases) that enter infected cells and trigger apoptosis (programmed cell death)
- Can release hydrogen peroxide which oxidizes and damages infected cells
Explanation: These two types of T-cells work together in a primary immune response. The T-helper cells act as the “command center” by activating other immune cells, while the T-killer cells are the “soldiers” that directly eliminate infected cells. This coordinated response is crucial for fighting viral infections effectively.
(b) Steps for global disease eradication:
- Universal vaccine availability: Make the vaccine free and accessible worldwide, including remote areas
- Herd immunity: Vaccinate a high percentage of the population to protect those who can’t be vaccinated
- Early childhood vaccination: Target children as they are most vulnerable to polio
- Surveillance and contact tracing: Monitor for cases and track potential outbreaks
- Ring vaccination: Immediately vaccinate all contacts when a case is detected
- Public education: Combat misinformation and explain vaccine benefits
- Cold chain maintenance: Ensure proper vaccine storage and transportation
- Record keeping: Track vaccinated individuals and identify gaps in coverage
- International cooperation: Coordinate efforts across borders and provide funding
- Trained personnel: Ensure enough healthcare workers to administer vaccines
Explanation: Eradicating a disease globally requires a comprehensive, multi-faceted approach. The key is achieving and maintaining high vaccination coverage everywhere, not just in developed countries. This means overcoming logistical challenges like vaccine distribution, addressing vaccine hesitancy through education, and having robust surveillance systems to detect and contain outbreaks quickly. The success of smallpox eradication and near-eradication of polio demonstrate that with sufficient resources and global cooperation, even highly infectious diseases can be eliminated.