# A person with HIV is said to have a weakened immune system. Explain why a person with HIV is more likely to develop serious infections than a healthy person, and describe the role of both T-lymphocytes and B-lymphocytes in a normal immune response to a pathogen.

> Pearson Edexcel A-Level Biology A (9BI0) — 5.3 Immune response · Explain · 5 marks

> HIV (Human Immunodeficiency Virus) is an infectious virus spread by direct contact with infected body fluids. It destroys white blood cells, weakening the immune system and may lead to AIDS (acquired immunodeficiency syndrome).

## Mark scheme (5 marks)

1. HIV destroys white blood cells, so the immune system is weakened / fewer white blood cells available to respond to pathogens
2. T-lymphocytes detect / respond to antigens (unique chemicals) on the surface of a pathogen
3. T-lymphocytes stimulate / activate B-lymphocytes to respond to the antigen
4. B-lymphocytes produce antibodies specific to the antigen on the pathogen
5. Because HIV destroys white blood cells (including T-lymphocytes), B-lymphocytes cannot be activated / fewer antibodies are produced, so the immune response is ineffective and serious infections develop

## Key terms

- [HIV](https://www.gradenine.co.uk/glossary/hiv)
- [T-lymphocyte](https://www.gradenine.co.uk/glossary/t-lymphocyte)
- [B-lymphocyte](https://www.gradenine.co.uk/glossary/b-lymphocyte)

## Related

- [Revision notes for Pearson Edexcel A-Level Biology A (9BI0)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-person-with-hiv-is-said-8bc006b7) · Published by Druglandscape Ltd.