Lv. Kozlov et al., Isotyping of component C4 of human complement using differences in the functional activity of isotypes C4A and C4B, BIOORG KHIM, 26(7), 2000, pp. 539-547
The difference in the functional activity of the isotypes A and B of compon
ent C4 of human complement was used to determine their ratio and to detect
the inherited deficiency of the isotypes. ELISA methods were developed for
the quantitative assay of component C4 (conventional sandwich method) and i
ts functional activity. When determining the functional activity, the class
ic pathway of the complement and therefore of component C4 was activated by
activators sorbed on ELISA microplates (immunoglobulin IgG3 or Liposacchar
ide of the Shigella sonnei cell walls, which activates the complement by bi
nding component C1). The nascent fragment C4b is covalently bound to the ta
rget activator; C4Ab binds better to the target protein (immunoglobulin), a
nd C4Bb to the target carbohydrate (liposaccharide). Therefore, when immuno
globulin is a target activator, isotype C4A is bound and determined; and wh
en the complement is activated by liposaccharide, isotype C4B is determined
. The ratio of the activities determined by the two methods indicates a def
iciency in the individual isotypes of component C4 or its absence. The rabb
it polyclonal monospecific antibodies against the human component C4 and th
e conjugates of these antibodies with horseradish peroxidase were used in t
he methods described.