Psychoneuroimmunology studies the effects of stress on the immune system.Identify the correct statements describing its working:

(A) The Leucocytes within the immune system identify and destroy antigens such as viruses.
(B) Stress does not affect natural killer cell cytotoxicity.
(C) Stress leads to the production of antibodies.
(D) There are several kinds of Leucocytes including the T cells, B cells, and natural killer cells.
(E) D-cells produce antibodies.

Choose the correct answer from the options given below:

The correct answer is the option containing (A), (C) (D) only.

Step-by-step Explanation:
Psychoneuroimmunology (PNI) is the study of how psychological processes, the brain and nervous system, and the immune system interact and influence each other. Let us evaluate each statement to understand why this option is correct:

1. Statement (A) is correct: Leucocytes, or white blood cells, are the primary cellular components of the immune system. Their main function is to identify, target, and destroy invading foreign particles or antigens, including viruses and bacteria.
2. Statement (D) is correct: Leucocytes are classified into different types based on their structure and function. Lymphocytes are a major category of leucocytes, which include T cells (essential for cell-mediated immunity), B cells (responsible for humoral immunity), and natural killer (NK) cells (which destroy infected or cancerous cells).

3. Statement (C) is correct: Stress triggers the release of stress hormones (like cortisol and catecholamines) through the activation of the hypothalamic-pituitary-adrenal (HPA) axis and the sympathetic nervous system. These hormones bind to receptors on immune cells, leading to changes in the immune response, which includes modulating the production of antibodies.
4. Statement (B) is incorrect: Research in psychoneuroimmunology shows that stress significantly suppresses the activity and cytotoxicity of natural killer (NK) cells rather than having no effect.
5. Statement (E) is incorrect: Antibodies are synthesized and secreted by activated B-lymphocytes (plasma cells), not D-cells (which are somatostatin-producing cells found in the stomach and pancreas).

Thus, statements (A), (C), and (D) are the only correct statements describing the working of psychoneuroimmunology and the immune system.