Abstract
A study was made of the changes in humoral immunity occurring during the early phases of experimental pneumococcus infection in the dog and cat, employing the methods devised by Robertson and Sia 1 for demonstrating the presence of anti-pneumococcus properties in the serum of animals naturally resistant to this microorganism. It was found that with a generalized and overwhelming infection accompanied by early blood invasion, there was a prompt and rapid decrease in the concentration of natural humoral immune bodies which frequently disappeared entirely by the time of death. This same early diminution of humoral immune substances, opsonins, agglutinins, and pneumococcidal promoting bodies was observed to occur in animals recovering from a moderately severe generalized infection with the difference that the concentration of immune bodies began to rise coincident with the onset of recovery. The decrease in concentration of humoral immune substances during a severe generalized infection appeared to be due to the combination of “S” substance with the normal immune bodies.
When the pneumococcus infection was more localized as in the case of true lobar pneumonia, a quite different sequence of events was observed to occur. Several animals in which extensive lobar pneumonia was produced showed well marked concentration of humoral immune bodies in the blood throughout the course of a fatally terminating infection.
These findings would suggest that after the inception of pneumococcus infection in the dog and cat the chief function of natural anti-pneumococcus substances in the blood is to limit or prevent blood invasion. In the presence of localized pneumococcus infection, the persistence of these circulating antibodies appears to have little effect either in preventing the spread of the process or determining the outcome of the disease.
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