Figure 2. hSAP mutants Y173A, Q174A, and Y173F/Q174L/T176V have reduced bioactivity compared with native hSAP.

PBMCs were cultured for 5 days in the presence of hSAP or an equal volume of SFM/buffer. Results are normalized to the number of fibrocytes in SFM, and the results are expressed as the mean percentage ± sem; n = 12 for native; n = 5 for S171A; n = 4 for Y173A and 173/174/176; and n = 3 for Q174A. (A) hSAP S171A did not have significantly reduced bioactivity compared with native hSAP as a result of the significant variance between assays (two assays showed reduced bioactivity; three assays showed a response similar to that of native SAP). (B–D) hSAP Y173A, Q174A, and Y173F/Q174L/T176V at 7.4 nM have significantly reduced bioactivity compared with native hSAP, as determined by t test; *P < 0.05; ***P < 0.001. (E) IC₅₀ values were obtained by fitting a sigmoidal dose response curve to the data. No significant differences were observed in the IC₅₀s between the mutants and native SAP (one-way ANOVA, Dunnett's test). If mutant S171A is excluded from the ANOVA analysis, mutants Y173A and Q174A have significantly increased IC₅₀ values compared with native hSAP, suggesting reduced hSAP bioactivity (P<0.01; one-way ANOVA, Dunnett's test).