Match the following types of white blood cells with their respective functions:

A. T cells

B. B cells

C. Natural killer cells

D. T-helper cells

i. Destroys invaders

ii. Produces antibodies

iii. Fights against viruses and tumors

iv. Increases immunological activity

A-i, B-ii, C-iii, D-iv

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.