Objective; To investigate the ability to remove different plasma proteins by double-filtration plasmapheresis (DFPP) using various primary separator and secondary separator combinations; based on it, to propose a novel DFPP therapy, and test its ability to eliminate MPO-ANCA from circulation of patients with vasculitides. Methodology;Fifteen patients with serum MPO-ANCA positive diagnosed as vaseulitides were enrolled and received 44 sessions DFPP. Three kinds of plasma filters were used to serve as primary and secondary filter, one plasma separator MPS07 and two plasma fraction separators EC50W, EC20W. There were three combinations; MPS07/EC50W, MPS07/ EC20W, and EC50W/EC20W combination; in each combination, the former was used as primary filter, and the latter was used as secondary filter. Double volume of plasma was processed, and 30 ~40g human albumin was supplemented during each session. One received 3 sessions DFPP using MPS07/EC50W, 9 received 27 sessions DFPP using MPS07/EC20W, and the other 5 patients received 14 sessions DFPP using EC50W/EC20W. During DFPP, waste plasma was discarded in intermittent way.When the pressure pre-secondary filter reached the threshold value to discard plasma, 800ml normalsaline was flushing the secondary filter to force filtration of plasma proteins accumulated in filter, before waste plasma was discarded. Sieving coefficients (SC) of albumin, IgA, IgG and IgM were measured for 3 filters, as well as reduction percentage of plasma proteins concentrations, MPO-ANCA titer by single session DFPP. Results: MPS07 filter was well permeable for all above-mentioned plasma proteins ( SC > 0. 6 ) ; while EC50W filter was well permeable for albumin and IgG, less permeable for IgA, and little permeable for IgM ( SC 0. 06) ; EC20W filter was permeable for only small proportion of albumin and IgG, much less for IgA, and impermeable for IgM ( SC 0. 03 ). Single session of DFPP had no effect on serum albumin level, but had diverse effects on other proteins concentration depending on filters combinations and proteins'type. During DFPP using MPS07/EC50W, decline of IgM, IgA, and IgG was (89. 7 ±5. 4)%, (61.7 ± 14.8)%, and(30. 5 ±9.0)% respectively. During DFPP using MPS07/EC20W, decline of IgM, IgA, and IgG was (94. 2 ±3. 1)% , (96. 2 ±2. 3)% , and (64. 7 ±21. 0)% respectively. During DFPP using EC50W/EC20W, decline of IgM, IgA, and IgG was (2. 80 ± 12. 9)% , (90. 9 ±4. 4)% , and (43. 5 ± 13. 8)% , respectively. Reduction percentage of MPO-ANCA titer by single session DFPP using EC50W/EC20W was (34. 6 ± 14. 3) %. Forced filtration of plasma in secondary filter by normal saline flushing before waste plasma discarding could raise the ratio of IgG/albumin concentration in waste plasma by 24. 2% . Conclusion: According to sieving coefficients of three kinds of filters for different plasma proteins, DFPP using EC50W/EC20W filters is better for removal of pathogens like IgG. With more selective removal of IgG, less loss of other larger useful molecules, it is effective to reduce serum ANCA titer.%目的：选择性血浆分离器行双重血浆置换(DFPP)，观察其对髓过氧化物酶型抗中性粒细胞胞质抗体(MPO-ANCA)清除。方法：15例临床诊断血管炎且血清MPO-ANCA阳性患者共接受44例次DFPP治疗。DFPP分三种方式，即MPS07/EC50W组合(血浆分离器MPS07作一级滤器，血浆成分分离器EC50W作二级滤器)；MPS07/EC20W组合(MPS07及EC20W分别作一、二级滤器)；EC50W/EC20W组合(EC50W及EC20W分别作一、二级滤器)。治疗剂量为处理2倍血浆容量，每次治疗补充人体白蛋白30～40g。其中1例患者采用MPS07/EC50W组合治疗3次，9例患者采用MPS07/EC20W组合治疗27次，余5例患者采用EC50W/EC20W组合治疗14次。DFPP采用间断弃浆方式，在弃浆前再使用生理盐水800 ml使二级滤器中蛋白再滤过后再弃浆。测定三种滤器对血浆白蛋白、IgA、IgG及IgM的筛选系数(SC)，及单次治疗前后血浆这些蛋白下降百分率，MPO-ANCA下降百分率,及清除指数。结果：MPS07血浆分离器能滤过血浆中多数蛋白，SC＞0.6；EC50W滤器能滤过血浆白蛋白及IgG，滤过IgA略差，IgM则不能滤过(SC 0.06)，EC20W滤器只能部分滤过白蛋白及IgG，滤过IgA更少，IgM不能滤过(SC 0.03)。三种方式DFPP单次治疗对血浆白蛋白影响不明显，MPS07/EC50W组合对血浆IgM清除最明显，IgA其次，IgG相对较差；MPS07/EC20W组合对三种免疫球蛋白清除都较好，尤以IgM及IgA更好；EC50W/EC20W组合对IgA及IgG清除较好，而对IgM无影响。采用EC50W/EC20W组合治疗单次IgG下降率达(43.5±13.8)％，MPO-ANCA滴度下降率(34.6±14.3)％，IgG清除指数0.47±0.15，MPO-ANCA清除指数0.34±0.09，白蛋白清除指数0.29±0.08。弃浆前采用生理盐水冲滤器可使废液中IgG/白蛋白比例提高24.2％。结论：对于清除以IgG为主的治疗，应选择EC50W/EC20W滤器组合方式以提高IgG清除的选择性，避免其他大分子物质丢失，有效降低血清MPO-ANCA滴度。
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