Assertion: Stress can affect natural killer cell cytotoxicity, which is of major importance in the defence against various infections and cancer.

Reason: T cells are attacked by the Human Immuno Deficiency Virus (HIV) causing Acquired Immuno Deficiency Syndrome (AIDS)

Assertion is true, but the Reason is false.

The immune system relies on the action of white blood cells, also known as leukocytes, to identify and eliminate foreign substances called antigens, such as viruses, bacteria, and other pathogens. White blood cells play a crucial role in the body's defense mechanisms by producing antibodies and directly destroying invaders. Within the immune system, there are different types of white blood cells, including T cells, B cells, and natural killer (NK) cells. T cells are responsible for directly attacking and destroying intruders, while T-helper cells enhance the immune response. T-helper cells are specifically targeted by the Human Immunodeficiency Virus (HIV), which leads to Acquired Immunodeficiency Syndrome (AIDS). B cells, on the other hand, produce antibodies that can recognize and neutralize antigens. NK cells have the unique ability to combat both viruses and tumors, making them an essential component of the immune system's defense mechanisms.

Stress has the potential to impact the functioning of natural killer (NK) cells, which play a crucial role in the body's immune response against infections and cancer. Research has shown that individuals experiencing high levels of stress, such as students facing important examinations, bereaved individuals, and those suffering from severe depression, tend to exhibit reduced levels of NK cell cytotoxicity.