Select the correct statement with respect to diseases and immunisation

Options

A. If due to some reason B-and T-lymphocytes are damaged, the body will not produce antibodies against a pathogen.
B. Injection of dead/inactivated pathogens causes passive immunity
C. Certain protozoans have been used to mass produce hepatitis B vaccine
D. Injection of snake antivenom against snake bite is an example of active immunisation

Explanation

To solve the question regarding the correct statement about diseases and immunization, we will analyze each option step by step.

### Step 1: Analyze Option A
- **Statement**: If due to some reason B and T lymphocytes are damaged, the body will not produce antibodies against a pathogen.
- **Explanation**: This statement is correct. B and T lymphocytes are crucial for the immune response. T cells help stimulate B cells to produce antibodies, which are essential for fighting off pathogens. If these cells are damaged, the body cannot effectively produce antibodies.

### Step 2: Analyze Option B
- **Statement**: Injection of dead or inactivated pathogens causes passive immunity.
- **Explanation**: This statement is incorrect. The injection of dead or inactivated pathogens leads to active immunity, not passive immunity. Active immunity occurs when the body produces its own antibodies in response to an antigen.

### Step 3: Analyze Option C
- **Statement**: Certain protozoans have been used to mass-produce hepatitis B vaccine.
- **Explanation**: This statement is also incorrect. The hepatitis B vaccine is produced using recombinant DNA technology, not protozoans.

### Step 4: Analyze Option D
- **Statement**: Injection of snake antivenom against snake bite is an example of active immunization.
- **Explanation**: This statement is incorrect. Snake antivenom is an example of passive immunity, as it provides immediate antibodies to neutralize the venom without the body having to produce them.

### Conclusion
After analyzing all options, the correct statement is:
- **Correct Answer**: Option A - If due to some reason B and T lymphocytes are damaged, the body will not produce antibodies against a pathogen.