What statement describes a systemic infection?

Rationale:

A. Anorexia, or loss of appetite, is a systemic response. It results from cytokine release and metabolic changes triggered by the immune system during infection. While it signals that the body is reacting to an infection, it does not indicate localized tissue involvement.

B. Exudate is a fluid containing proteins, immune cells, and cellular debris that collects at the site of infection. It can appear as serous fluid, purulent pus, or sanguineous drainage, depending on the pathogen and tissue affected. Exudate is a hallmark of localized inflammation and serves to isolate the infection and facilitate immune cell activity.

C. Fever is a systemic manifestation caused by pyrogens—substances released by immune cells or pathogens—that act on the hypothalamus to raise body temperature. Fever reflects the body’s overall immune response, not a localized tissue effect.

D. Pain occurs due to inflammation and tissue damage at the infection site. Chemical mediators such as prostaglandins, bradykinin, and histamine stimulate nociceptors, causing discomfort. Pain alerts the body to tissue injury and can help limit movement or pressure on the affected area, preventing further damage.

E. Weakness or fatigue is also a systemic effect, resulting from energy diversion to immune activity, metabolic shifts, and cytokine release. It reflects the overall stress on the body rather than a localized immune response.

Rationale:

A. Proteins that bind to antigens are antibodies (immunoglobulins). Mast cells are cells, not proteins, and their primary role is not to directly bind to antigens.

B. Direct destruction of pathogens or abnormal cells is the role of phagocytes, cytotoxic T cells, and natural killer cells. Mast cells do not directly kill pathogens, but instead orchestrate the immune response by releasing chemical signals that recruit other immune cells.

C. The primary function of mast cells is to release preformed chemical mediators stored in granules, including histamine, heparin, prostaglandins, and cytokines. Histamine causes vasodilation and increased capillary permeability, allowing immune cells to move into tissues. Cytokines recruit additional immune cells, such as neutrophils and eosinophils, to the site of infection or injury. Prostaglandins and leukotrienes contribute to inflammation, pain, and bronchoconstriction. Mast cells are central to allergic reactions, such as urticaria (hives), asthma, and anaphylaxis, because the rapid release of mediators can cause tissue swelling, redness, itching, and airway constriction. They also help in defense against parasitic infections.

D. Antibodies are immunoglobulin proteins, not cells. Mast cells release chemical signals rather than directly attacking tissues. While mast cells can contribute to tissue damage during allergic or autoimmune reactions, they themselves are not antibodies.