No difference have been observed in the properties of amyloid P-component (AP) and its serum counterpart (SAP) which might account for the deposition of the former in amyloidosis. Purified by nonselective techniques, preparations of AP and SAP were shown to have similar molecular weights and peptide composition, identical morphology in the electron microscope (EM) and to be antigenically indistinguishable. Both proteins were soluble in EDTA but readily precipitated in the presence of calcium ions, forming characteristic two-dimensional arrays in the EM. In serum however, SAP was not aggregated and sedimented at 9.5S in Ca2+ as did the purified protein in EDTA. Precipitation of purified SAP by calcium could be prevented by pretreatment with acid hydrolysates of agarose or SP Sephadex, matrices for which SAP has a calcium-dependent affinity. It is proposed that SAP circulates in combination with a low molecular weight natural ligand which prevents its aggregation. While the identity of natural ligand for SAP is as yet unknown, it is likely to resemble the glycosidic subunits in agarose.
Normal red blood cells (RBC) from fresh EDTA and CPD blood and from stored CPD blood were examined for the presence of bound subcomponents of C3 and C4. By serologic agglutination tests, only C3d was detectable on the cells. Incubation in compatible fresh normal serum (FNS) at 37 degrees C appeared to increase the amount of 3Cd on the RBC. C3b was serologically detectable only on stored CPD cells and only after incubation in compatible FNS. No. C4 components were detected on the cell surfaces in agglutination tests. Using an indirect labeling technique, small, but significant, amounts of C3d and C4d were found on all three types of untreated cells. C3b was present on stored CPD cells only. The indirect labeling technique showed a significant increase in C3d and C4d on all cells following incubation i- compatible FNS, whereas bound C3b was significantly increased only with stored CPD cells. There was no increase in bound C4b following serum incubation. The average number of C3d molecules per cell on normal EDTA cells was 557 and average Ko was 3.6 x 10(7) l/mol.
The presence of small amounts of C3d on freshly obtained normal red blood cells (RBC) was demonstrated by a radio-labelled antiglobulin technique; this increased 1.5-fold after incubation in fresh normal serum. No significant further increase in bound C3d was demonstrated for cDE/cDE, CDe/CDe, -D-/-D- RBC maximally sensitized with any of three potent anti-D antibodies. When anti-c, anti-D and anti-E antibodies were used in combination to sensitize cDE/cDE RBC, bound C3d increased by approximately 22%; however, a similar increase occurred with cde/cde RBC and was therefore considered non-Rh specific. Umbilical cord RBC from four infants severely affected by anti-D haemolytic disease of the newborn did not exhibit more bound C3d than cord RBC from normal controls. One serum containing IgM anti-M bound a small amount of complement in vitro; two IgG anti-M sera did not.
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