The Opsonins of Normal and Immune Sera
Authors: Ecker E. E. , Pillemer L. , Kuehn A. O. 
Published: January 2023

Summary and Conclusions
No relationship exists between the hemolytic complementary and opsonic powers of the guinea-pig, human, monkey (rhesus), dog, cat and sheep sera toward staphylococci.
Normal sheep and bovine sera show the highest opsonic values.
The normal opsonins of guinea-pig, human, monkey, sheep, dog, cat and rabbit sera are for the most part thermolabile.
The CO2-soluble fraction of the guinea-pig serum which contains the endpiece and its associated fourth component of complement carries also the antistaphylococcic opsonic agent of this serum.
In the human serum the CO2-soluble fraction also contains the greater portion of the normal human serum antistaphylococcic opsonin.
In the serum of the rhesus monkey the antistaphylococcic opsonins appear to be distributed between the CO2-soluble and CO2-insoluble fractions, the major portion being in the CO2-soluble fraction.
Sheep-serum antistaphylococcic opsonins are readily destroyed by heat as well as by the relatively mild agents employed in the fractionation of the guinea-pig serum. One-third of the sheep-sera examined showed exceedingly high opsonic values.
A separation of the dog-serum proteins by CO2 demonstrates that the anti-staphylococcic opsonic factor or factors are not carried independently by either the CO2-precipitate or by the CO2-soluble fractions. A combination of these two fractions yields a full opsonic value.
The antistaphylococcic opsonins of cat-serum appear to be distributed between the CO2-soluble and the CO2-insoluble fractions, the major portion occurring in the CO2-soluble fraction. The treatment of rabbit-serum with zymin greatly enhances its antistaphylococcic opsonic value. Ammonia does not destroy this opsonic activity. CO2, however, markedly destroys the antistaphylococcic opsonin of this serum.
The treatment of staphylococci with concentrated human serum (1:1) and subsequently with an antistaphylococcic serum also in a 1:1 dilution leads to a reduction in the number of cocci ingested by human leucocytes. A similar result is obtained when the cocci are first heated with the immune serum. In the latter case, however, and at the optimal concentration of the immune serum, the addition of the inactivated human serum definitely increases the number of cocci ingested.
In general, rhesus monkey-serum gives the same results. At optimal dilutions of the monkey-serum and the antiserum an actual enhancement of phagocytosis is observed.
Phagocytosis of staphylococci treated with concentrated sheep-serum and later with a highly diluted antistaphylococcic serum is markedly enhanced. This is, however, not the case when the cocci are first treated with the immune serum prior to the addition of the diluted normal serum.
Dilution of the sheep-serum or inactivation of this serum leads to a great reduction in the opsonic effects of the combined sera.
The treatment of staphylococci with a 1:40 normal dog-serum and 1:64 anti-staphylococcic serum results in an enhancement of phagocytosis. Inactivated dog-serum does not show this synergistic effect.
Cat-serum shows a distinct enhancement of phagocytosis in the proper concentrations of cat-serum and the immune serum. Even inactivated cat-serum in the presence of optimal amounts of the immune serum, shows this enhancing action.
Rabbit-serum also shows a less marked enhancing effect when the cocci are first treated with the optimal concentration of the antiserum followed by a very dilute normal rabbit-serum. Inactivated rabbit-serum does not enhance phagocytosis in the presence of the antistaphylococcic serum.
The differences encountered in the human, monkey- and cat-sera as compared with the sera of the other species investigated are probably due to the fact that these sera contain along with the thermolabile opsonin also a thermostable opsonin. It is therefore difficult to differentiate the effects of these two opsonins.