White blood cells (purple and gold circles) attack and destroy a chain of streptococci (red, disrupted chain at center). Streptococci are bacteria that can cause strep throat. White blood cells play an important role in the body's defense against agents of disease.
SECTION 1 Nonspecific Defenses
SECTION 2 Specific Defenses: The Immune System
SECTION 3 HIV and AIDS
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