Abstract
Lymphoid cells are unable to lyse antibody-coated target cells in the presence of normal immunoglobulin G (IgG), presumably because their surface receptors of IgG are blocked. However, when target cells are sensitized with antibodies and complement, IgG receptors are unblocked and cytotoxicity occurs even in the presence of normal IgG. Thus, IgG receptors may function in vivo despite the relatively high concentations of IgG in serum and interstitial fluid.