An analysis of neutralization reaction of interferon by antibody: a proposal on the expression of neutralization titer.

Methods of determining and expressing the neutralization titer of anti-interferon antibody were discussed based on considerations of the mass-action law and on experimental data of neutralization of L cell interferon by various antisera. The antibodies in all the sera so far examined were inferred to have low affinities (low association constants compared to the reciprocal of molar concentrations of free interferon), regardless of whether the serum had a low (a few hundred) or high (over 10(5) titer. Then the equilibrium equation can be approximated by a simple formula which relates the antibody concentration to the ratio of total to free interferon concentrations; the absolute amount of interferon neutralized (the difference between total and free interferons) is not involved in computing the titer, and therefore the problem of variations in interferon sensitivity in different assays is eliminated. It is proposed that the neutralization titer be defined, not as the antibody dilution that neutralizes a certain quantity of interferon (such as 10 international units, as often found in the literature), but as the dilution that reduces the interferon titer by a certain factor (taken to be 10 in this paper). A simple formula for calculating the titer from experimental data is given.