The ability of an individual to resist infection by means of normally present body functions is called

The ability of an individual to resist infection by means of normally present body functions is called

• A. Innate immunity
• B. Humoral immunity
• C. Adaptive immunity
• D. Cross-immunity

Answer: (A)

Innate immunity is the body’s immediate, non-specific defense that is present from birth. It includes physical barriers like skin and mucous membranes, chemical defenses, and immune cells such as phagocytes and natural killer cells, plus the complement system. These defenses operate without prior exposure or learning, providing resistance to infections through normally present body functions. That’s why it fits best: the description highlights resistance that comes from existing, non-specific defenses rather than antibodies or memory-based responses. Humoral immunity refers to antibodies produced by B cells and is part of the adaptive, specific response. Adaptive immunity is the targeted, memory-forming system that strengthens with exposure. Cross-immunity describes partial protection against a related pathogen due to immunity to another, not the general, always-present defenses.

Innate immunity is the body’s immediate, non-specific defense that is present from birth. It includes physical barriers like skin and mucous membranes, chemical defenses, and immune cells such as phagocytes and natural killer cells, plus the complement system. These defenses operate without prior exposure or learning, providing resistance to infections through normally present body functions.

That’s why it fits best: the description highlights resistance that comes from existing, non-specific defenses rather than antibodies or memory-based responses. Humoral immunity refers to antibodies produced by B cells and is part of the adaptive, specific response. Adaptive immunity is the targeted, memory-forming system that strengthens with exposure. Cross-immunity describes partial protection against a related pathogen due to immunity to another, not the general, always-present defenses.