Complement attaches to immunoglobulin at -

Antigen is attached to Fab region Complement and ADCC(antibody dependent cellular cytotoxicity) attachment are through Fc region. The constant region of the heavy chain has many biological functions. It is responsible for activation of the complement, binding to cell surface receptors, placental transfer, and many other biological activities. The amino-terminal half of the light or heavy chain, consisting amino acids, is known as variable or V regions (VL in light chains and VH in heavy chains).These antigen-binding sites are responsible for specific binding of antibodies with antigens. The high specificity of antibodies is primarily due to the presence of these hypervariable regions.