Which of the following best describes the components of the immune system?

• A. Adaptive immunity, innate immunity including surface barriers and leukocytes, humoral immunity, inflammation mediators, and the complement system.
• B. The immune system consists only of adaptive immunity.
• C. Adaptive immunity, innate immunity including surface barriers and leukocytes, humoral immunity (IgA, IgD, IgE, IgG, IgM, T and B cells), inflammation mediators (histamine, bradykinin, serotonin, leukotrienes, prostaglandins), and the complement system.
• D. The endocrine system plays a central role in immunity.

Answer: (C)

Understanding the immune system means recognizing two main arms: innate and adaptive. The innate part provides immediate defense and includes surface barriers such as skin and mucous membranes, plus leukocytes like neutrophils and macrophages that respond to invaders. It also involves a set of inflammatory mediators—substances like histamine, bradykinin, serotonin, leukotrienes, and prostaglandins—that orchestrate increased blood flow, vascular permeability, and recruitment of immune cells. The complement system is part of this innate response, helping to opsonize pathogens and form membrane attack complexes.

The adaptive arm provides a targeted, learned response and is divided into humoral immunity, driven by antibodies produced by B cells, and cellular immunity, driven by T cells. The humoral side includes classes of immunoglobulins (IgA, IgD, IgE, IgG, IgM) that neutralize pathogens and mark them for destruction.

Putting these together, the description that includes adaptive immunity, innate immunity with surface barriers and leukocytes, the antibody classes, the inflammatory mediators, and the complement system captures the full range of immune components. The endocrine system is not the central framework for describing immune components.