Rabbit antisera prepared against interferon produced in human fibroblast cell cultures stimulated with poly(I) -poly(C) neutralized the activity of interferon preparations produced in various human fibroblast cultures stimulated either with poly(I) poly(C) or with viruses. However, these antisera showed no detectable neutralizing activity against interferon produced in cultures of human leukocytes. On the other hand, most rabbit antisera against the human leukocyte interferon were active in neutralizing both homologous interferon and fibroblast interferons. A preparation of antiserum against leukocyte interferon, active against both leukocyte and fibroblast interferons, was shown by affinity chromatography to have two distinct antibody populations, one of which was specific for the fibroblast interferon. We conclude that the heterologous neutralizing activity of sera from rabbits immunized with leukocyte interferon is likely to be due to the presence of two antigenic species of interferon. The major antigenic species of leukocyte interferon preparations (designated "Le") is distinct from human fibroblast interferon. The minor species of leukocyte interferon ("F") is either identical with, or closely related to, interferon produced in human fibroblast cultures.
streptococci, and with sera of human subjects. 2. Evidence was obtained that complementfixing antigenic material in such preparations was not identical with the complement-fixing fractions obtained from streptococcal cells, and complement fixation was probably not due to any of a number of the extracellular enzyme-antigens which can be found in streptococcal culture supernates. -_. --I _ _ ---1. Paul, J. R., and other contributors, The epidemiology of rheumatic fever and some of its public health aspects, ed. 2 , New York, Metropolitan Life Tnsurnnce Company, 1043. STREPTOCOCCAL ANTIGENS 39
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