ABSTRACT
A small percentage of the Western population carries antibodies in the peripheral blood, which are able to kill human tumors such as neuroblastoma or melanoma. Several observations indicate that these antibodies, preferentially of IgM isotype, belong to the class of naturally occurring antibodies. Here, we describe two screening methods for the detection and quantification of such antibodies in human blood samples: a cellular ELISA technique and a flow cytometric assay, based on intercalation of fluorescent propidium iodide into the DNA of dying or dead cells.
Subject(s)
Antibodies/blood , Antibodies/immunology , Cytotoxicity, Immunologic , Neoplasms/blood , Neoplasms/immunology , Cell Line, Tumor , Flow Cytometry/methods , HumansABSTRACT
A small percentage of healthy donors identified in the Western population carry antibodies in their peripheral blood which convey cytotoxic activity against certain human melanoma and neuroblastoma cell lines. We measured the cytotoxic activity of sera and plasmas from healthy donors on the human neuroblastoma cell line Kelly and various melanoma cell lines. Antibodies of IgM isotype, presumably belonging to the class of naturally occurring antibodies, exerted cytotoxic activity in a complement-dependent fashion. Apart from complement-dependent tumor cell lysis, we observed C3 opsonization in all tumor cell lines upon treatment with cytotoxic plasmas. Cell lines tested primarily expressed membrane complement regulatory proteins (mCRP) CD46, CD55 and CD59 to various extents. Blocking of mCRPs by monoclonal antibodies enhanced cell lysis and opsonization, though some melanoma cells remained resistant to complement attack. Epitopes recognized by cytotoxic antibodies were represented by gangliosides such as GD2 and GD3, as evidenced by cellular sialidase pretreatment and enhanced expression of distinct gangliosides. It remains to be clarified why only a small fraction of healthy persons carry these antitumor cytotoxic antibodies.
