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To develop resources for large-scale production of human fibroblast interferon, we isolated, cryopreserved, and characterized 15 new strains of human diploid foreskin fibroblasts. Their life spans in vitro ranged from 52 to 72 population doublings. We based the selection of cell strains for mass interferon production on the number of population doublings during which consistently high yields of interferon were obtained after "superinduction" in roller bottles; our data show that aging in vitro leads to significant decline in amounts of interferon produced. In contrast, susceptibility to interferon remains largely unaffected by in vitro senescence. Karyotypic analysis indicated that the best interferon-producing strain, MLD (over 60,000 reference units/ml), has a translocation between chromosomes 5 and 15.

The effect of rifampicin on the immune response to sheep red blood cells and the lipopolysaccharide antigen of Escherichia coli in mice and to cholera vaccine in human volunteers was studied. No evidence of an immunosuppressive effect of the drug was found in humans given doses not exceeding those clinically recommended. Primary response was depressed in mice when a large dose of rifampicin was given ip soon after the administration of the antigen. The phagocytic activity of the peritoneal macrophages from mice given rifampicin ip was profoundly curtailed. The correlation between depression of the immune response and reduction of phagocytic activity strongly suggests that the main target of the drug is the phagocytosing cell.