The suffix "-penia" in medical terminology is used to signify a deficiency. This means that the amount is abnormally low. The prefix "leuko-" can also be found in the word leukocytes, which is another word for white blood cells. As a result, leukocytopenia means abnormally low white blood cell levels.

Erythropenia is a condition in which erythrocyte counts (red blood cells) are low.

Innate immunity is a generalized defense system against invading pathogens and foreign materials. In other words, these defenses are already found in the body and do not need to see a pathogen before becoming present. Plasma cells arise from B-lymphocytes, and must interact with an antigen from a pathogen in order to proliferate in the body.

Skin, stomach acid, and granulocytes (such as neutrophils) are constant presences in the body that help defend against pathogens.

Increased nutrient availability would increase bacterial cell growth, while all the other answers decrease ability of bacteria to grow in culture.

The immune system consists of two components, the innate (non-specific) and the adaptive (specific) arms. These components work together to prevent infection, clear established infections, and to protect against disease or foreign bodies. The innate (non-specific) system consists of barriers, the complement cascade, and other specialized cells. Barriers include saliva, tears, skin, mucous linings, stomach acid, and "good" gut bacteria (this outcompetes bad bacteria).