The Innate and Adaptive Immune Systems Collaborate, Increasing the Efficiency of Immune Responsiveness

It is important to appreciate that adaptive and innate immunity do not operate independently – they function as a highly interactive and cooperative system, producing a combined response more effective than either branch could produce by itself. Certain immune components play important roles in both types of immunity.

An example of cooperation is seen in the encounter between macrophages and microbes. Interactions between receptors on macrophages and microbial components generate soluble proteins that stimulate and direct adaptive immune responses, facilitating the participation of the adaptive immune system in the elimination of the pathogen. Stimulated macrophages also secrete cytokines that can direct adaptive immune responses against particular intracellular pathogens.

Just as important, the adaptive immune system produces signals and components that stimulate and increase the effectiveness of innate responses. Some T cells, when they encounter appropriately presented antigen, synthesize and secrete cytokines that increase the ability of macrophages to kill the microbes they have ingested. Also, antibodies produced against an invader bind to the pathogen, marking it as a target for attack by complement and serving as a potent activator of the attack.

A major difference between adaptive and innate immunity is the rapidity of the innate immune response, which utilizes a pre-existing but limited repertoire of responding components. Adaptive immunity compensates for its slower onset by its ability to recognize a much wider repertoire of foreign substances, and also by its ability to improve during a response, whereas innate immunity remains constant. It may also be noted that secondary adaptive responses are considerably faster than primary responses. Principle characteristics of the innate and adaptive immune systems are compared in Table 1.With overlapping roles, the two systems together form a highly effective barrier to infection.

Table 1

Comparison of adaptive and innate immunity