The first line of defense involves which structure (s) ?

A - T-cells,

B - skin,

C - blood,

D - B-cells

The correct answer is option B, that is, skin.

Explanation:

The innate immune system is considered as the first line of defense. This immune system is formed of defenses against the infections, which can be stimulated instantaneously after the attack of a pathogen. The innate immune system is basically formed of barriers, which works to keep bacteria, viruses, parasites, and other foreign agents away from the body or restrict their tendency to disperse and move all over the body.

The innate immune system comprises physical barriers like the gastrointestinal tract, skin, the nasopharynx, the respiratory tract, and body hair. It also comprises defense mechanisms like mucous, secretions, tears, saliva, sweat, and gastric acid. Apart from this innate immune system also comprises certain general immune responses like complement, inflammation, and non-specific cellular responses.

Your answer is B - skin.