Pneumococcal septicaemia and anti-pneumococcal immunity

Abstract

The object of the investigation recorded herein has been to enquire into the mechanism by which pneumococci are removed from the blood stream of the rabbit after intravenous injection and to see how far this process is modified by immunization.

It has seemed most convenient to divide the text into two parts. In the first will be described at length the experiments that have been made, reference to the literature being made only where necessary to elucidate the point discussed: in the second part these experimental results are discussed and compared with those reported by other workers.

SUMMARY: 1. Virulent pneumococci inoculated into a normal rabbit undergo rapid removal for a short period but subsequently increase in numbers.

2. Aviralent pneumococci are removed more rapidly and do not reappear in the blood.

3. Immunization enhances the capacity of the animal to remove virulent organisms and prevents their reappearance.

4. This improvement can be detected to a slight extent five hours after injection of killed culture, but becomes marked three days thereafter. It has been observed to last as long as ten months after immunisation.

5. The outstanding effect of immunisation with Type I. pneumococci is the enhancement of activity of the body fluids favouring phagocytosis but the existence of a slight residual purely cellular immunity cannot be altogether excluded.

6.. Agglutinins, opsonins, precipitins, complement fixing antibodies do not appear to be essential as such to this improvement.

7. The blood of a normal rabbit-is bactericidal to avirulent pneumococci or inhibits their growth. It has no such action upon virulent pneumococci.

8. Blood of an immunized rabbit is destructive to virulent pneumococci or delays their growth. The property of delaying the commencement of growth appears earlier and lasts far longer than any other antibody activity tested.

9. The destructive action of the blood is of a:much lower order than of the animal as a whole.

10. The leucocytes may be considerably reduced without interfering with the capacity of the animal to dispose of organisms introduced into the blood.

11. "Blocking" of the ret:ículo-endothelial system has proved similarly ineffective.

12. This is thought to be due to the complexity of the clearing mechanism involving as it does a variety of phenomena of adhesion and phagocytosis by mutually complementary systems of cells.

13. Virulent pneumococci injected in the phase of latency behave in vivo as in vitro. The increase occurring some time after injection is due to their passing into the phase of active growth.

14. Virulent pneumococci introduced in the active phase of growth do not undergo the preliminary rapid removal.