ABSTRACT
This chapter considers some features of the efferent limb of the immune response. It also considers immunoglobulins and antibodies from the structural and biological viewpoints. The activation of the effector systems may depend on a conformational change in the antibody molecule which occurs on combination of the antibody with its antigen. The antigen-antibody complex may not only activate effector systems but may also feed back into the regulatory mechanisms determining qualitative and quantitative aspects of the immune response as it progresses. The formation of a precipitate is dependent on the relative concentrations of antigen and antibody, and precipitates will not form in great antigen excess or antibody excess. Most of what is known about humoral immunity depends upon a few relatively simple assay systems which are designed to detect the presence of antibody activity, in some cases to dissect it qualitatively and to give some degree of quantitation.
