Question

Ag processing cells are

• A. Eosinophils
• B. Basophiles
• C. Lymphocytes
• D. Macrophages

Hint:

The "Big Three" APCs:
1. Macrophages.
2. Dendritic Cells.
3. B-Lymphocytes.
In fish immunology questions, Macrophages are the most common answer for phagocytosis and antigen processing.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
"Ag processing cells" refers to Antigen-Presenting Cells (APCs). The question asks to identify which of the listed immune cells in fish serves this function.
Detailed Explanation:

• Antigen Presentation: For the adaptive immune system to recognize a pathogen, the pathogen's proteins (antigens) must be digested and "presented" on the cell surface in association with Major Histocompatibility Complex (MHC) molecules.

• Role of Macrophages: Macrophages are professional phagocytic cells. In fish, as in mammals, they ingest pathogens, process the antigens, and present them to T-lymphocytes to initiate a specific immune response. Therefore, they are the primary "Ag processing cells."

• Analysis of other options:
• Eosinophils/Basophils: Granulocytes involved in inflammatory and parasitic responses, but not primary APCs.

• Lymphocytes (C): These are the receivers of the presented antigens (T-cells) or producers of antibodies (B-cells), but they are not categorized primarily as "processing cells" in this functional context.

Step 3: Final Answer:
Macrophages are the primary Ag processing (Antigen-Presenting) cells among the options.