Nurse shark C1 (C1n) was incompatible with rabbit IgG or IgM but could be hemolytically measured with sheep erythrocytes sensitized with natural nurse shark antibody (EAn). C1n was precipitated from nurse serum by dilution with 4.0 M urea to µ = 0.04 at pH 7.3 and 0°C. The precipitate was washed twice in µ = 0.15 Veronal-buffered saline (VBS++) and then dissolved in µ = 0.25 VBS++. The resulting C1n preparation had high specific activity but was still contaminated with nurse IgM. When optimally sensitized EAn were reacted for 20 min at 30°C with 90 effective molecules of C1n per cell in isotonic dextrose gelatin Veronal buffer (DGVB++) (µ = 0.12, pH 6.9), maximum reactivity of the resulting new intermediate cell (EAnC1n) was obtained. These cells could be specifically lysed with guinea pig serum devoid of C1 or whole guinea pig serum dilutions, since EAn did not react with guinea pig C1. C1n transfer from EAnC1n or the corresponding stroma to EAn was mainly dependent on the ionic strength. Antibody transfer could also be demonstrated, but antibody and C1n did not transfer as a unit. Mixed intermediate complexes: EAnC1n4gp, EAnC4gp could be formed.

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