“…Sera were obtained for this study from several hundred patients prior to and at several time intervals following injection therapy with alum-precipitated pyridine extracted ragweed pollen (7). Hemagglutinin antibody titers to the whole ragweed extract were determined by standard tanned cell hemagglutinin techniques using sheep erythrocytes coated with an optimum concentration of whole, defatted ragweed pollen extract (3)(4)(5). In addition, sera were also tested for 'classic' blocking antibody titexs axxd for skin sensitizing (reaginic) antibody (2-4).…”