Step 1: Understanding the Concept:
The thymus is a primary lymphoid organ located in the upper part of the chest, behind the sternum.
It is most active during childhood and begins to shrink (atrophy) after puberty.
Its primary function is to serve as the "school" or maturation site for T-lymphocytes (T-cells).
While all lymphocytes are produced in the bone marrow, those destined to become T-cells must migrate to the thymus to undergo differentiation and maturation into functional immune cells.
Step 2: Detailed Explanation:
1. Role of T-lymphocytes: Mature T-cells are the primary mediators of Cell-Mediated Immunity (CMI). This system is responsible for fighting intracellular pathogens (like viruses and some bacteria), fungi, and cancer cells. They are also responsible for the rejection of foreign tissue grafts.
2. Types of T-cells: These include Helper T-cells (\( T_H \)), which coordinate the immune response, and Cytotoxic T-cells (\( T_C \)), which directly kill infected cells.
3. Consequences of Thymectomy: If the thymus is removed during early childhood (before it has finished maturing the body's pool of T-cells), the site for T-cell development is lost. This leads to a severe deficiency of functional T-lymphocytes in the blood and secondary lymphoid organs.
4. Impact on Immunity: Without T-cells, Cell-Mediated Immunity is severely impaired. Furthermore, because Helper T-cells are required to activate B-lymphocytes for most antibody productions, humoral (antibody-mediated) immunity is also weakened, though CMI is the primary and most direct casualty.
Therefore, option (C) correctly identifies the primary physiological deficit.
Step 3: Final Answer:
Thymectomy in early life results in impaired cell-mediated immunity due to the lack of mature, functional T-lymphocytes.