SUMMARY

Analysis of the neutralization of human interferon-or by the monoclonal antibody NK2 showed, by three different methods, that the avidity constant was about 101 ° M- 1. A small decrease in the avidity constant (and in the antibody titre) with increasing interferon concentrations was observed, suggesting that the antibody-interferon complex had a little biological activity. The antibody neutralizes the interferon by preventing the binding of interferon to susceptible cells. It does not react with human-% mouse-or, monkey, bovine or rabbit interferons. Secher & Burke (1980) first reported the isolation of a monoclonal antibody to human interferon-or (IFN-c0. In contrast to other monoclonal antibodies which have been isolated more recently (Montagnier et al., 1980; Staehelin et al., 1981), Secher & Burke selected their antibody, called NK2, by screening for neutralization of the antiviral effect of human IFN-ct, while other investigators have usually used radiolabelling methods. Recently, Novick et al. (1983) have used a new screening procedure based on immune precipitation with a second antibody and recovery of interferon activity from the immune precipitate. The NK2 antibody is thus, because of the selection procedure used, a neutralizing antibody, and since it was screened against he mixtur