GENERATION OF COMPLEMENT ACTIVATION PEPTIDES DURING STORAGE OF PLATELET CONCENTRATES (PC)
Platelets are routinely stored for transfusion at room temperature in autologous, citrated plasma. We have demonstrated previously that these conditions do not completely block activation of plasma enzyme systems, as indicated by generation of thrombin activity (Vox Sanguinis, JL1:192,1986). Here, we demonstrate the conversion of large amounts of complement factor C3 during storage of citrated PC by using radioimmunoassay quantitation of the activation peptide C3a des-Arg (Upjohn Diagnostics). Supernatant samples from stored PC and from citrated platelet-poor plasma (PPP) stored under the same conditions showed a rapid linear increase in C3a levels over time with no significant difference (paired t-test, p<0.5) between PC and PPP (see table). The values at Day 10 represent conversion of approximately 11% of the native C3. Possible effects on stored platelets of C3 conversion in the surrounding plasma include:activation of platelets by C3a des-Arg (M.Polley and R. Nachman; J.Exp.Med. 158:603, 1983) and deposition of C3b on the cell surface as "innocent bystanders" (A. Salama and C. Mueller-Eckhardt; Transfusion 25:528,1985).In contrast, <10 ng/mL C5a was found in all samples tested, representing less than 0.2%conversion of C5a.Nephelometricassay of native C5 levels in PC samples showed a slight but significant difference by a paired t-test (p=0.04) between fresh PC (mean=117 ug/mL±12.0, n=6)and P stored for 10 days(nean=108 ug/mL±9.7). Nochange in C5 levels was observed in stored PPP (106 ug/mL to 107 ug/mL). Radiolabelled monoclonal antibodies to C3 fragments showed less than 600 molecules bound per platelet. This study demonstrates for the first time the extent of complement activation in stored platelet concentrates.