Immunoglobulin Peptide with Complement Fixing Activity

Abstract

INDIVIDUAL immunoglobulin molecules often possess several biological activities in addition to reactivity with appropriate antigen. Such activities include complement fixation, skin sensitization, attachment to macrophages and the tissue fixation required for placental passage^1,2. Some members of this protein group lack one or more of these capacities: human IgG γ4 myeloma molecules and human IgD are unable to fix complement, for example^3,4. Hill et al.⁵ suggested, on the basis of their observation of repeating amino-acid sequences in immunoglobulins, that these molecules might have arisen by a series of gene duplications, and Edelman et a1.⁶ have recently proposed that certain repeating regions of immunoglobulin polypeptide chains might have been selected for participation in biological effector functions such as complement fixation (domain hypothesis). According to this concept it should be possible to associate a complement fixation function with a specific submolecular domain in certain immunoglobulin molecules.