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. 2007 Nov;5(4):227-40.
doi: 10.2450/2007.0047-07.

Factors affecting the antigen-antibody reaction

Roberto Reverberi  1 , Lorenzo Reverberi
Affiliations

Factors affecting the antigen-antibody reaction

Roberto Reverberi et al. Blood Transfus. 2007 Nov.
No abstract available

Keywords: antibody; antibody affinity; antigen; antigen-antibody reaction; equilibrium constant.

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Figures

Figure 1
Figure 1
Effect of increasing the equilibrium constant on three representative red cell antibodies. The y-axis on the left shows the number of IgG per red cell. The y-axis on the right is the agglutination strength corresponding to the number of IgG/cell (the correlation is based on a study by Merry et al. and must be intended as a gross approximation; it is shown for illustrative purposes only). Anti-D, -c, and – K are supposed to have an equilibrium constant of 2′108, 4.4′107, and 1.5′1010, respectively (typical values, see Table III) and a concentration below the minimum detectable in the antiglobulin test. If the equilibrium constant is increased 10 to 1,000 times, anti-D and anti-c are greatly enhanced but anti-K is not. The reason is that, in the initial conditions, anti-D and anti-c only have 17 and 13%, respectively, of the antibody molecules bound to the red cells, while anti-K already has 79%. Therefore, in the latter case, increasing the equilibrium constant 1,000-fold results in a mere 20% increment in antibody uptake, too small to be appreciated in the antiglobulin test.
Figure 2
Figure 2
Effect of the dilution of the reaction system on antibody uptake. Y-axes are the same as in figure 1. Antibodies are also the same, but they are supposed to have an initial concentration corresponding to a ‘++’ in the antiglobulin test. If a suitable medium is added, which dilutes the system without changing temperature, pH, or ionic strength, anti-D and anti-c are markedly affected and the antibody uptake may be insufficient to be detected. A high affinity antibody, such as anti-K, is much less affected.
Figure 3
Figure 3
Effect of an increased serum/cell ratio on antibody uptake. Y-axes and antibodies are the same as in previous figures. In the initial conditions, antibodies are supposed to have a concentration equal to half of the amount necessary to give a ‘+’ in the antiglobulin test. A serum/cell ratio of 40 corresponds to two volumes of serum/plasma for one volume of 5% red cells. Higher ratios are obtained by adding more serum/plasma. Anti-K is greatly enhanced. In contrast, the uptake of low affinity antibodies (anti-D and anti-c) is only modestly increased.
Figure 4
Figure 4
Effect of antigen zygosity on the number of antibodies per cell. Y-axes and antibodies are the same as in previous the figures. Dark and light bars represent homozygous and heterozygous red cells, respectively. Calculations are based on the following estimates for the number of antigen sites per cell: homozygous cells: D: 27,000, c: 78,000, K: 5,000; heterozygous cells: D: 12,000, c: 40,000, K: 3,000. The antibodies (anti-D, -c, -K) are supposed to have such a concentration as to give a ‘++’ in the antiglobulin test with homozygous cells. In the case of low affinity antibodies (anti-D and antic), the use of heterozygous instead of homozygous cells causes a marked decrease in the number of IgG/cell. The high affinity antibody (anti-K) is much less affected.
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References

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