The number of acidophils increase during  

Options

A. bacterial infection
B. viral infection
C. protozoan infection
D. Allergic reaction & flat worm infections

Answer

To answer the question "The number of acidophils increase during:", we will analyze the options provided and determine which one is correct based on our understanding of the immune response.

### Step-by-Step Solution:

1. **Understanding Acidophils**: Acidophils, also known as eosinophils, are a type of white blood cell that play a crucial role in the immune response, particularly in combating parasitic infections and allergic reactions.

2. **Analyzing the Options**:
- **Bacterial Infection**: During bacterial infections, neutrophils (another type of white blood cell) increase in number to fight off the bacteria. Acidophils do not significantly increase in response to bacterial infections. Therefore, this option is incorrect.

- **Viral Infection**: In viral infections, the body typically produces interferons and activates lymphocytes, particularly T-cells. Acidophils are not primarily involved in the response to viral infections, making this option incorrect as well.

- **Protozoan Infection**: Protozoan infections can lead to an increase in eosinophils, as these cells are involved in fighting off larger parasites. However, this option is not the most relevant for acidophils specifically.

- **Allergic Reaction**: Allergic reactions are characterized by an increase in eosinophils (acidophils). These cells respond to allergens and play a significant role in the inflammatory response associated with allergies.

3. **Conclusion**: Based on the analysis, the correct answer is that the number of acidophils increases during **allergic reactions**.

### Final Answer:
The number of acidophils increases during **allergic reactions**.