Personal immunity versus social immunity

Personal immunity versus social immunity

Many organisms defend their fitness against attack from parasites and pathogens by mounting an immune response. Most physiological immune responses are internal and targeted at organisms that have invaded the body. For example, invertebrates show innate responses to parasites by producing antimicrobial peptides and lysozymes that either inhibit the growth of microorganisms or kill them. Similarly, their blood cells phagocytose single-celled parasites, whereas larger invaders are encapsulated in a layer of blood cells that are melanized, sealing off the invader from the host’s body (Rolff and Reynolds 2009). Vertebrates additionally have an adaptive immune response comprising lymphocytes that respond to antigens on the surface of the parasite, and these provide a targeted response with immunological memory (Janeway et al. 2001). In addition to this typical internal response, some defenses are deployed externally to overcome microorganisms in the environment.