During assessment of a client diagnosed with severe anemia, the nurse notes pallor of the skin and mucous membranes. Which explanation is the best rationale for this finding?

Choice A reason: Decreased dietary intake of proteins and vegetables is not the best explanation because it is a factor that affects the nutritional status, not the immune system. Nutritional status is important for maintaining the health and function of the body, but it does not directly cause an increased risk of infection. Proteins and vegetables are sources of essential nutrients, such as amino acids, vitamins, minerals, and antioxidants, that support the growth and repair of the tissues and the prevention of oxidative stress.

Choice B reason: Decreased T cell function and antibody response is the best explanation because it is a factor that affects the immune system, which is the body's defense mechanism against foreign invaders, such as bacteria, viruses, and fungi. The immune system consists of two main components: the innate immunity and the adaptive immunity. The innate immunity is the first line of defense that provides a general and rapid response to any potential threat. The adaptive immunity is the second line of defense that provides a specific and long-lasting response to a particular antigen. T cells and antibodies are part of the adaptive immunity, which recognizes and remembers the antigens that have previously infected the body and eliminates them more efficiently. However, as people age, the T cell function and the antibody response decline, making the older adults more susceptible to infections, especially those that are new or unfamiliar to the body.

Choice C reason: Atrophy of the bone marrow and spleen is not the best explanation because it is a factor that affects the production and storage of immune cells, not the function and response. The bone marrow is the soft tissue inside the bones that produces the blood cells, including the white blood cells, which are the main components of the immune system. The spleen is an organ that filters the blood and removes the old or damaged blood cells, as well as stores some of the white blood cells and platelets. As people age, the bone marrow and the spleen shrink and lose some of their ability to produce and store the immune cells, which can reduce the number and diversity of the immune cells available to fight infections. However, this does not necessarily affect the function and response of the immune cells that are already circulating in the blood.

Choice D reason: Impaired absorption of vitamin B12 is not the best explanation because it is a factor that affects the nervous system and the blood cells, not the immune system. Vitamin B12 is a water-soluble vitamin that is essential for the synthesis of DNA, the maintenance of the myelin sheath, and the formation of red blood cells. As people age, the absorption of vitamin B12 decreases due to the reduced secretion of stomach acid and intrinsic factor, which are needed to break down and bind to the vitamin B12 in the food. This can lead to vitamin B12 deficiency, which can cause symptoms such as fatigue, weakness, numbness, tingling, memory loss, and anemia. Anemia is a condition where the blood has a low level of hemoglobin, which is the protein that carries oxygen in the red blood cells. Anemia can affect the oxygen delivery to the tissues, but it does not directly cause an increased risk of infection.

Choice A reason: Infected macrophages and lymphocytes surround the Mycobacterium tuberculosis bacteria and form a tuberculous granuloma is the best explanation for the primary immune response to tuberculosis infection. A granuloma is a collection of immune cells that wall off the bacteria and prevent their spread. It is a protective mechanism that limits the infection and preserves the lung function.

Choice B reason: Tumor necrosis factor is released by T lymphocytes and lyses the Mycobacterium tuberculosis bacteria in the alveoli is not a correct explanation for the primary immune response to tuberculosis infection. Tumor necrosis factor is a cytokine that activates macrophages and induces inflammation, but it does not directly kill the bacteria. It may also have harmful effects by causing tissue damage and weight loss.

Choice C reason: Natural killer cells and neutrophils form a thick purulent debris, which becomes a caseous necrosis is not a correct explanation for the primary immune response to tuberculosis infection. Natural killer cells and neutrophils are part of the innate immune system, which is not very effective against intracellular bacteria like Mycobacterium tuberculosis. Caseous necrosis is a type of tissue death that results from the liquefaction of the granuloma. It is a sign of progressive disease, not primary infection.

Choice D reason: The inflammatory response of cytokines activates the complement system and causes permanent lung tissue damage is not a correct explanation for the primary immune response to tuberculosis infection. The inflammatory response of cytokines and the complement system are part of the innate immune system, which is not very effective against intracellular bacteria like Mycobacterium tuberculosis. Permanent lung tissue damage is a complication of chronic or reactivated tuberculosis, not primary infection.