Which is the proper order of events cell mediated immunity?

Options

A. Antigen enters tissue, marcophages engulf antigen, antigen presented to members of a clone of lymphocytes sensitised T-lymphocytes attack antigen -bearing agents
B. Antigen enters tissues, antigen passed to members of a clone of lymphocytes , lymphocytes sensitised , macrophages engulf antigen, T-lymphocytes attack antigen-bearing agents
C. Antigens enters tissues, macrophages engulf antigen, antigen passed to members of a clone of lymphocytes, lymphocytes sensitised, B-lymphocytes secrete antibodies that react with antigen-bearing agents
D. Antigen enters tissues, lymphocytes sensitised antigen passed to members of a clone of lymphocytes , macrophages engulf antigen, T-lymphocytes attack antigen -bearing agents.

Answer

### Step-by-Step Solution for the Question: "Which is the proper order of events in cell-mediated immunity?"

1. **Entry of Antigen**: The process begins when an antigen enters the tissue. This can occur through various means, such as infection or injury.

2. **Presentation of Antigen**: The antigen is then processed and presented on the surface of antigen-presenting cells (APCs), such as macrophages, in conjunction with Major Histocompatibility Complex (MHC) molecules.

3. **Activation of Lymphocytes**: The T lymphocytes (specifically, cytotoxic T cells) recognize the MHC-antigen complex. This recognition leads to the sensitization and activation of these lymphocytes.

4. **Cytokine Secretion**: Activated T cells secrete cytokines, which play a crucial role in further activating other immune cells, including helper T cells and macrophages.

5. **Macrophage Activation**: The cytokines released stimulate macrophages, enhancing their ability to engulf and destroy pathogens.

6. **Destruction of Pathogens**: Finally, the activated T lymphocytes attack the antigen-bearing cells through mechanisms such as apoptosis (programmed cell death), effectively killing the infected or abnormal cells.

### Conclusion
The proper order of events in cell-mediated immunity is:
1. Antigen enters the tissue.
2. Antigen is presented by MHC on APCs.
3. Lymphocytes are sensitized and activated.
4. Macrophages are activated and engulf the antigen.
5. T lymphocytes attack and kill the antigen-bearing cells.