There are two broad categories of immunity involved in host defense – natural or innate and acquired. While natural immunity is more generalized, acquired immunity is more specific and adaptive. There are various levels of host defense that protect human body from invading attacks.
These are
Physical barriers
- Natural (Innate) immunity: Skin, mucous membranes
- Acquired Immunity: Mucosal immune system
Circulating factors
- Natural immunity: Complement, C reactive protein
- Acquired Immunity: Antibody
Cells
Natural immunity: Macrophages, neutrophils, Natural killer cells
Acquired Immunity: Lymphocytes
Cytokines
Natural immunity: Monokines (IL-1, TNF, IL-12, interferons)
Acquired Immunity: Lymphokines (interleukins)
