Effect of a Heat-Resistant Enzyme Upon the Antigenicity of Pneumococci

Abstract

Rabbits immunized by the intr a cutaneous injection of heat-killed encapsulated pneumococci fail to develop the type-specific carbohydrate antibodies which result from the intravenous injection of the same antigen. 1 An attempt was made to follow the fate of pneumococci injected into the skin, in the hope of determining the cause of this lack of type-specific antigenic response.

Heat-killed cells of pneumococcus Type I were injected at several sites into the skin of a rabbit. The injected areas were excised at different intervals of time and films made from the tissue fragments were stained by the Gram technic. There was, of course, a pronounced polymorphonuclear infiltration at the site of injection. The pneumococci were seen to undergo a process of extracellular digestion which began within 24 hours after injection and was completed in 4 to 5 days; many bacteria became Gram negative before being engulfed by the leucocytes. These observations suggested that leucocytes produce ferments capable of attacking heat-killed pneumococci.

To demonstrate the existence of these enzymes, a polymorphonuclear exudate was obtained by injecting aleuronate into the pleural cavity of a rabbit. The washed cells extracted with N/10 HQ yielded a soluble principle which has the property of rendering pneumococci Gram negative. Active extracts, with similar properties, were obtained from the organs—especially the liver, pancreas, spleen, and lungs—of several animal species. The same enzyme was also prepared from the pleural exudate from a tuberculous patient, who developed empyema following secondary infection with H. influenza.

The active enzyme present in these extracts is heat-resistant, especially at slightly acid reactions. Its rate of activity upon pneumococci increases with temperature up to 75°C.; the range of pH activity lies between pH 5.5 and pH 9.5. The enzyme appears to be a protein which is rapidly destroyed by pepsin but is completely resistant to trypsin and chymotrypsin.