Cells, Tissues, and Mediators

The activation, maturation, differentiation, and mobilization of immune cells are controlled by cytokines (e.g., interleukins, interferons, and chemokines), which are soluble mediators produced by immune cells and/or by cells outside the immune system (e.g., epithelial cells and cells of the nervous system). Other soluble (humoral) mediators produced by immune cells include antibodies (immunoglobulins) and complement proteins (plasma proteins produced by monocytes and macrophages as well as hepatocytes). Mediators are important in the implementation and regulation of immune responses. 

Immune responses are divided into innate responses directed nonspecifically against foreign substances and acquired responses directed against specific antigens (see Table 32.2 for important definitions). Innate immunity is generally viewed as the 

Molecules (proteins or carbohydrates) that evoke specific immune responses usually foreign to the host. 

Soluble proteins known as immunoglobulins these molecules circulate freely and react specifically with invoking antigen subclasses IgM, IgG, IgE, IgD, and IgA. 

Series of nonimmunoglobulin plasma proteins sequentially activated by antigen-antibody complexes. They damage target cell membranes and are active in host defense. 

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