On the Heat Stability of the Diphtheria Toxin

The property of heat sensitiveness is considered as a characteristic of bacterial exotoxins. In a previous paper (2), however, we have pointed out that a part of the scarlatinal toxin could stand boiling for thirty minutes. It seems rather curious that the scarlatinal toxin is an exception to this general rule. In order to analyse this general rule—heat sensitiveness of exotoxins—we examined carefully the heat stability of the diphtheria toxin as a typical exotoxin and found that a part of the diphtheria toxin also could stand boiling for thirty minutes.

Five portions of diphtheria toxin No. 166 (pH 8.5; m.l.d. = 1/300 cc.) heated to varying temperatures (60°, 70°, 80°, 90°, and 100°C.) for thirty minutes were tested for their m.r.d. on two guinea pigs and it was found that the ratio of m.r.d. of the heated toxins and that of unheated control was 50 (60°C.), 500 (70°C.), 2,000 (80°C.), 10,000 (90°C.) and 10,000 (100°C.) respectively.

Studies on the “Toxins” of Hemolytic Streptococci

The specific toxin has been almost completely precipitated by the addition of 2 volumes of alcohol both from culture filtrate and from the broth culture itself, and easily obtained in a form of solution by simple saline extraction of this precipitate. The specific toxin is not easily dialyzable. No precipitation occurred when 2 volumes of alcohol were added to one volume of dialyzed culture filtrate, but abundant precipitate of the specific toxin was observed when in addition to alcohol a small amount of saturated salt solution was added to the dialyzed filtrate. A small portion of the specific toxin may be precipitated by acid from a culture filtrate, dialyzed filtrate and crude specific toxin (solution of alcoholic precipitate). When the alcoholic precipitate of specific toxin was dissolved in a small amount of saline solution, an insoluble part remained. The suspension and the washings from this insoluble part caused positive skin reactions on white pigs, while the washings from an acid precipitate of the culture filtrate or crude specific toxin gave no skin reaction on the same animals even in a higher concentration. Accordingly, the acid precipitate seems to contain the specific toxin not merely by adsorption, but perhaps in a form of chemical combination, probably, with nucleoprotein.

Studies on the “Toxins” of Hemolytic Streptococci

The so-called nucleoproteins obtained from the bacterial sediments of a 0.5 per cent glucose broth culture of Streptococcus scarlatinæ by Woolridge's method, even in a highly diluted solution, gave a positive skin reaction in human beings which is indistinguishable from that caused by the ordinary Dick toxin. This substance is non-toxic for man and for the usual laboratory animals, it does not cause a skin reaction in white pigs, and its action is relatively heat-stable, but easily destroyable by tryptic digestion. When a culture filtrate of Streptococcus scarlatinæ (Dick toxin) is adjusted to pH about 4.0 with the addition of hydrochloric or acetic acid, a small precipitate occurs. This precipitate seems to be nucleoprotein in nature, as (a) it was precipitated by an antinucleoprotein serum which was prepared by the immunization of rabbit with nucleoprotein described above, (b) it did not cause a positive skin reaction in white pigs, (c) 86.2 per cent of 44 school boys tested, reacted in a similar manner to the intracutaneous injection of both the nucleoprotein solution and the solution of this acid precipitate from a culture filtrate, while 74.9 per cent of them reacted inversely to these solutions and to the specific toxin. A specific toxin was obtained from a culture filtrate of Streptococcus scarlatinæ in a relatively pure form by the repetition of alcohol- and acid-precipitation. This toxin may cause a positive skin reaction in both human beings and white pigs, as the culture filtrate itself. Skin reactions of human beings to this toxin and to the ordinary Dick toxin were in accordance with each other in the majority of cases examined (1241 individuals). The action of this toxin was practically destroyed by heating at 80°C. for thirty minutes and was neutralized by scarlatinal antitoxin. It is toxic for man and rabbit. Immunity may be obtained by injection of this purified toxin into susceptible human beings, and in the course of this immunization, the scarlatinoid syndrome was observed in some boys. This substance may, therefore, be considered to be the essential scarlatinal toxinexotoxin of Streptococcus scarlatinæ. The skin reaction to the so-called Dick toxin seems to be due to the presence of these two components, exotoxin and bacterial protein. The skin reaction to the bacterial protein seems to indicate an allergic state to this protein and that to the exotoxin is an indication of susceptibility to the specific exotoxin of Streptococcus scarlatinæ. For the susceptibility test to scarlet fever purified exotoxin free from bacterial proteins should be used. With respect to the response to the specific toxin and the nucleoprotein solution human beings may be grouped into four classes: The persons belonging to the first group are not only not immune or highly susceptible to the specific toxin, but also they are not allergic to the bacterial proteins of streptococcus; and those of the second group are allergic to the same proteins, but still susceptible to the specific toxin. The third group consists of persons who are immune to the specific toxin, but still allergic to the proteins; and persons of the fourth group are those who are not only immune to the specific toxin, but also not allergic to the bacterial proteins. In the first place, the specific toxin purified by us is heatlabile and seems not to act as an allergen; secondly, it may be neutralized by its antitoxin which may be produced by the immunization of horses or human beings with scarlatinal toxin or by suffering from scarlet fever, and also it may render positive reactors immune to this specific toxin by subcutaneous injections of it; and thirdly it may cause the scarlatinoid syndrome following an injection of a certain dose of it in highly susceptible human beings. For these three reasons the symptoms of scarlet fever may be interpreted as the intoxication caused by the exotoxin of Streptococcus scarlatinæ, but it can not be explained as an allergic phenomenon, as some authors believe. The white pig proved to be suitable as a test animal for the titration of scarlatinal toxin and antitoxin. For the same purpose a member of the first group of persons in our sense only may be suitable as a test object, if the ordinary Dick toxin be employed, but any person who is not sensitive to horse serum may be useful if purified exotoxin is available. If one uses the skin reactions in human beings as a criterion for the purification of scarlatinal toxin, it may happen that only the nucleoproteins are purified, while the specific toxin is lost. White pigs or persons of the first group in our sense must be used for this purpose. But, it must be borne in mind that even persons of the first group may give a positive skin reaction to a highly concentrated solution of nucleoproteins. Our crude, concentrated toxin prepared by precipitation with two volumes of alcohol from a culture filtrate may be conveniently used for the immunization and hyper-immunization of horses, as it can be concentrated more than ten times.

Variation in Susceptibility to Diphtheria Toxin Among Guinea Pigs and Rabbits and Accuracy of Various Methods of Toxinantitoxin Titration

The sensitiveness of the skin of guinea pigs and rabbits to a small amount of diphtheria toxin shows considerable variation locally and individually. The skin of the side-chest and flank gives a uniform and more marked reaction to the injection of a small amount of diphtheria toxin than the skin of the abdomen. Abnormally low skin sensitiveness to diphtheria toxin is an indication of antitoxin content in the blood serum. We propose to define the term “susceptibility” as follows: Susceptibility is expressed by the m.l.d. of one toxin determined with guinea pigs of average susceptibility divided by the m.r.d. of the same toxin on the guinea pig or rabbit tested. The introduction of this idea of susceptibility would yield more accurate experimental results in regard to the assay of toxin and antitoxin. Individual variation in susceptibility to diphtheria toxin among guinea pigs was considerable, and the susceptibility varied from 2000 to 75 in our tests with almost 300 guinea pigs. Normal susceptibility seems to be from 1000 to 500. The susceptibility to diphtheria toxin of rabbits varied from 3000 to 500 in our tests with 30 rabbits. Pregnancy and littering seem temporarily to reduce very much the skin sensitiveness to diphtheria toxin. The m.r.d. and the Lr/500 dose of a given toxin showed considerable variation according to the varying susceptibility of the guinea pig employed for titration. The Roemer method of toxin-antitoxin titration, therefore, must be conducted as follows: the m.r.d. or the Lr/500 dose of a given toxin is determined from the ratio of the m.r.d. or the Lr/500 dose of test toxin to that of a standard toxin tested on the same guinea pig, at the same time. Male guinea pigs over 400 grams weight are preferable as test animals for the intracutaneous method. By the Schick test we are enabled to discover the guinea pig of abnormal susceptibility which might cause irregularities in the result of the determination of m.l.d. of a diphtheria toxin. Individual variation of susceptibility among guinea pigs might have some influence on the determination of the “Immunity index.”

Schick Test as Applied to the Selection of Horses for the Production of Diphtheria Antitoxin

That horses possessing natural antitoxin in their blood produce antitoxin readily is well known by workers (Hitchens and Tingley, Hida, Glenny, Wadsworth, Sordelli, Ramon, etc.) in this field. Park and Zingher pointed out that persons yielding negative Schick tests respond to toxin-antitoxin injections with the production of antitoxin more readily than those who react in a positive manner.

In the selection of such naturally immune horses for the purpose of immunization a trial bleeding is usually taken and the serum is tested for natural antitoxin by Römer's cutaneous method or Ehrlich's subcutaneous method. Hitchens and Tingley injected 0.2 cc. diphtheria toxin, equaling 3 m.l.d.'s for 250 gram guinea pigs, into the conjunctiva of one eye of horses under examination for the purposes of immunization, and found that many yielded negative tests read at the end of forty-eight hours, indicating the presence of natural diphtheria-antitoxin in the blood of normal horses.

On the Natural Immunity to Scarlet Fever of the Japanese and Chinese Residing in South Manchuria

Southern Manchuria, where the Chinese, as the native race and the Japanese, as immigrants, live under the same environment affords an appropriate field to study racial differences of natural immunity.

Experienced physicians here believe that the morbidity in scarlet fever of the Japanese is far greater than that of the Chinese. According to the investigation of antiscarlatinal committee of the Kwantung Government the morbidity of the Japanese residents is 3.06 per cent while that of the Chinese is only 0.12 per cent. These figures were obtained by dividing the number of scarlet fever cases occurring between 1921 and 1925 and treated by hospital and civil physicians attached to the S. M. R. Company by the number of the population living during the same period within the area under the jurisdiction of the Local Affairs Department of the S. M. R. Company. While these figures generally seem to be correct, the fact that there are some scarlet fever cases among the Chinese failing to make returns, should be taken into consideration.