A blood treatment system for treating acute inflammatory diseases mediated by mediators, comprising at least one first device and at least one second device, - wherein the at least one first device has a first blood-side flow path for conducting blood, and the at least one second device has a second blood-side flow path for conducting blood, and wherein the at least one first device and the at least one second device are connected serially, one after the other, such that the first blood-side flow path is fluidically connected to the second blood-side flow path, - wherein the at least one first device is a membrane filter for removing toxic mediators from blood, and the at least one second device is suitable for removing granulocytes and monocytes from blood; and - wherein the membrane filter has a housing, a filter interior formed in the housing, and a semi-permeable membrane arranged in the filter interior, said membrane subdividing the filter interior into a retentate space and a permeate space, - wherein the housing has a blood inlet device and a blood outlet device which are fluidically connected to the retentate space, and the blood inlet device, the retentate space, and the blood outlet device form the first blood-side flow path for conducting blood through the first device, and - wherein the housing furthermore has a permeate outlet for discharging the permeate flowing through the semi-permeable membrane from the permeate space, - wherein the semi-permeable membrane has an ultrafiltration rate in water UFRwater ranging from 500 to 2000 mL/(h m 2 mmHg), and the membrane filter has a separating characteristic such that the filter coefficient for albumin, SK Alb, ranges from 0.05 to 0.3, and the filter coefficient for immunoglobulin G (IgG), SK IgG, ranges from 0.001 to 0.1. - wherein the at least one first device has a first blood-side flow path for conducting blood, and the at least one second device has a second blood-side flow path for conducting blood, and wherein the at least one first device and the at least one second device are connected serially, one after the other, such that the first blood-side flow path is fluidically connected to the second blood-side flow path, - wherein the at least one first device is a membrane filter for removing toxic mediators from blood, and the at least one second device is suitable for removing granulocytes and monocytes from blood; and - wherein the membrane filter has a housing, a filter interior formed in the housing, and a semi-permeable membrane arranged in the filter interior, said membrane subdividing the filter interior into a retentate space and a permeate space, - wherein the housing has a blood inlet device and a blood outlet device which are fluidically connected to the retentate space, and the blood inlet device, the retentate space, and the blood outlet device form the first blood-side flow path for conducting blood through the first device, and - wherein the housing furthermore has a permeate outlet for discharging the permeate flowing through the semi-permeable membrane from the permeate space, - wherein the semi-permeable membrane has an ultrafiltration rate in water UFRwater ranging from 500 to 2000 mL/(h m 2 mmHg), and the membrane filter has a separating characteristic such that the filter coefficient for albumin, SK Alb, ranges from 0.05 to 0.3, and the filter coefficient for immunoglobulin G (IgG), SK IgG, ranges from 0.001 to 0.1.