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Mammals have both kinds of defense mechanisms, and these mechanisms are the focus of this chapter. In mammals, the innate and adaptive mechanisms operate together as a coordinated defense system. Table 41.1 gives an overview of these defenses during the course of an infection. Innate immunity is the body’s first line of defense because the adaptive defenses often require days or even weeks to become effective.
| Response time | System | Mechanisms |
|---|---|---|
| Early (0- |
Innate, nonspecific (first line) | Barrier (skin and lining of organs) |
| Dryness, low pH | ||
| Mucus | ||
| Lysozyme, defensins | ||
| Middle (> 4- |
Innate, nonspecific (second line) | Inflammation |
| Phagocytosis | ||
| Natural killer cells | ||
| Complement system | ||
| Interferons | ||
| Late (> 96 hr) | Adaptive, specific | Humoral immunity (antibodies from B cells) |
| Cellular immunity (T cells) |