See also: Basis of EndoCAb ELISA (studies on normal individuals)
The EndoCAb ELISA was used to determine EndoCAb values for 1022 healthy adults (volunteer blood donors). A blend of four high IgG-EndoCAb sera were used as the standard (control): plates were developed with gamma, mu or alpha heavy-chain specific conjugates to determine IgG, IgM or IgA values. The results were determined initially as a percentage of the control: the medians of each range was determined and values were converted to median-units (MU) by setting the median value as 100 (%). Thus normalised, the normal ranges of each Ig class were similar with the 10th percentile at 35MU and the 90th percentile at 250MU (approximately). It should be noted that the GMU, MMU and AMU are relative, and are not equivalent in absolute quantitative terms.
For IgG-EndoCAb-hyperimmune plasma the cut-off is set at 400 GMU/ml. 43 individuals (4.2%) were above cut-off. This plasma has been used to prepare EndoCAb-hyperimmune intravenous gammaglobulin (IVIG) or fresh-frozen plasma (FFP) for clinical use.
The EndoCAb ELISA was designed initially, after extensive studies of different plasma to a wide range of LPS in ELISA, as a valid immunoassay for detection, selection and quantitation of plasma with high titres of LPS-cross-reactive IgG so that such plasma could be used for preparation of EndoCAb-hyperimmune intravenous gammaglobulin for clinical use. The following figure shows the reactions of IgG prepared from individual donors' plasma to a range of individual LPS, in ELISA. The different IgG preparations were all used at the same total IgG concentration.
The hyperimmune EndoCAb plasma gave IgG with extensive high titer cross reactivity on a wide range of LPS. In most cases this cross reactivity can be completely absorbed out on a single rough-LPS (Ra or Rc) bacterial strain, indicating that the reactions observed are mostly cross-reactive, not polyspecific (Scott, Barclay, Smith et al. (1990)).
EndoCAb hyperimmune intravenous gammaglobulin was prepared from a pool of naturally-immune high EndoCAb titer blood donor plasma, obtained by plasmapheresis.
Normal values of EndoCAb for infants and children have been determined. The early contribution of maternal IgG can be seen in infant's' early IgG EndoCAb. There is a decline following birth to a minimum at around 90 days. This is the time when cot death or SIDS is at a maximum (see Oppenheim et al: References). Both IgM and IgG EndoCAb climb from 90 days towards low to median adult values by one year.
Values of IgG EndoCAb stabilise around the adult median by around 5 years. Values for IgM EndoCAb overshoot the adult median and climb well above the adult range at the start of the teens, returning towards normal in the later teens. The findings of high IgM EndoCAb in some studies of meningococcal septicaemia (unpublished) needs to be interpreted against this finding that IgM EndoCAb tends to be high in teenagers.
See Barclay, 1995: References