Cyanate as an inactivator of complement proteins
Schultz, D.R.; Arnold, P.I.
Journal of Immunology 115(6): 1558-1565
1975
ISSN/ISBN: 0022-1767 PMID: 1184967 Document Number: 85136
Sodium cyanate [NaNCO] added to normal human serum or serum from patients with sickle-cell disease resulted in the functional inactivation of C3 [the 3rd complement component], C5, C6, C7 and the C3b [b fragment of C3] inactivator, but not C8 and C9. Final concentrations as low as 0.5 mM in serum caused inactivation of 12-64% of the C3 after 8 h at 37.degree. C. The activity of the inactivated C3, C5 and C3b inactivator was not restored by dialysis. Most of the functional activity of C3 in NaNCO-treated sera was destroyed by very small quantities of 14C-labeled NaNCO that was bound to the protein. C3 inactivation by NaNCO occurred in heated sera (50.degree. C, 30 min) and sera treated with EDTA, probably indicating that 1 mechanism for inactivation was by a direct carbamylation reaction. C3 and C5 showed 2 anodal-migrating forms in 2 dimensional antigen-antibody crossed electrophoresis in some sera treated with low concentrations of NaNCO. Measurements of circular dichroism of highly purified carbamylated C3 showed no detectable changes in structure even though most of the functional activity was destroyed. Purified, inactive C3 that was carbamylated with 14C-labeled NaNCO was capable of binding to EAC142 [sheep erythrocyte, rabbit antibody, C1 through C2], but the resulting EAC1423 was weakly positive for immune adherence and negative for agglutination with anti-C3 antiserum. Unlabeled, cell-bound C3b on EAC142 was not susceptible to NaNCO action as shown by no loss in immune adherence and positive agglutination with anti-C3 antiserum. The C3b inactivator was more susceptible to NaNCO than C3 in a short time period; both were inactivated after 8 h. Since cyanate is currently being evaluated as a treatment for sickle-cell disease, the inactivation of C3 by the drug is an important consideration for such patients who are already deficient in C3 dependent heat-labile opsonins that aid in host defense.