Presence of Type Specific Pneumococco-opsonins in Sera of Animals Naturally Resistant to Pneumococcus Infection.

In a previous communication, Robertson and Sia 1 found that the sera of animals, such as cat, dog, sheep and pig, that are naturally resistant to pneumococcus infection, contained normal opsonins for the pneumococcus, whereas the sera of susceptible animals did not possess such opsonic power for pneumococci virulent for the species. In the course of that study it soon became evident that the serum from a resistant animal, under proper conditions, could be shown to opsonize pneumococci belonging to any of the various serological groups. The question whether the sera of naturally resisant animals contain a common pneumococco-opsonin for all pneumococci, or separate opsonins for each type of the organism immediately arose. The results of Bull and McKee 2 in demonstrating the existence of separate protective substances in normal chicken serum for each type of pneumococcus, together with the author's findings, reported in a previous paper, 3 on the specific effect of pneumococcus soluble substance on the growth of pneumococci in normal serum-leucocyte mixtures, suggest that the sera of resistant animals may contain separate pneumococco-opsonins, specific for each type of pneumococcus. The present report deals with a study which has in view the elucidation of this point.

In this work, sera from two species of naturally resistant animals were used, namely, cat and pig. The method consisted of absorbing the sera by one of the three fixed types of pneumococcus and then testing the opsonic content of the absorbed sera for all the three types. The percentage of polyrnorphonuclear leucocytes taking part in phagocytosis was recorded and compared with that of control sera which were similarly treated except that no pneumococci were added.

The results thus obtained were very striking. It was found that the absorbed serum lost all of its opsonins for the particular type of pneumococcus employed in the absorption, while those for the other two fixed types were very little affected.