Rescue of properdin gene knockout by NEO deletion. (A) Schematic diagram showing expected recombinant properdin gene locus after FLPe-mediated NEO deletion. (B) PCR genotyping of 7 mice derived from properdin^−/− × FLPe-transgenic mouse crossing. Using LoxP or FLPe-specific primers, 2 mice (numbers 1 and 5) were identified as having recombinant properdin gene and 4 mice (numbers 1-4) were FLPe transgenic. As expected, the FLPe-negative, LoxP-positive mouse (number 5) contained NEO, whereas the FLPe-positive, LoxP-positive mouse (number 1) did not contain NEO. (C) Immunodiffusion analysis of plasma properdin showing that no properdin was present in mouse 5 (properdin^−/−), whereas properdin was detected in mouse 1 (knockout rescued). Antihuman properdin antibodies were placed in the center well, and plasma samples for mice 1, 2, 5, and 6 (B) were placed in the peripheral wells.