Figure 2.1. The response to an initial infection occurs in three phases.

Figure 2.1The response to an initial infection occurs in three phases

The effector mechanisms that remove the infectious agent (for example, phagocytes and complement) are similar or identical in each phase, but the first two phases rely on recognition of pathogens by germline-encoded receptors of the innate immune system, whereas adaptive immunity uses variable antigen-specific receptors that are produced as a result of gene rearrangements. Adaptive immunity occurs late, because the rare B and T cells specific for the invading pathogen must undergo clonal expansion before they differentiate into effector cells that can clear the infection.

From: Chapter 2, Innate Immunity

Cover of Immunobiology
Immunobiology: The Immune System in Health and Disease. 5th edition.
Janeway CA Jr, Travers P, Walport M, et al.
New York: Garland Science; 2001.
Copyright © 2001, Garland Science.

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