82
A. SARAGEA ET AL.
protection against all C. diphtheriae strains capable of causing toxaemic
diphtheria.
Toxin was obtained in-a crystalline form by Pope and Stevens in 1958.
The minimum lethal dose (MLD), which for the most active purified
preparations is less than 40 ng, was originally defined by Ehrlich as that
amount of toxin required to kill a 250g guinea pig on the fourth day,
following subcutaneous injection with three characteristic signs : gelatinous
and/or haemorrhagic oedema and local swelling at the site of inoculation,
adrenal congestion and haemorrhagic or clear exudate in the pleural and
peritoneal cavities. A few picograms injected into rabbit skin will produce
a visible reaction. As detailed above the toxin is very antigenic and is
neutralised by antitoxin.
Treatment with formalin converts toxin into an antigenic but non-toxic
product: toxoid (English), anatoxin (French). The specific intoxication
produced by the exotoxin in vivo can be specifically neutralised by antitoxin, and this reaction is important both for performing the Schick test in
man and as a rapid method of toxin-antitoxin titration in animals.
Large quantities of toxin are used for the preparation of toxoids as
prophylactics and as antigens, to obtain antitoxin in horses for passive
immunisation and for testing individual susceptibility to diphtheria by
means of the Schick test.
During the last decades highly immunogenic prophylactics have been
obtained by purification of diphtherial toxoid, and adsorption on aluminium
salts (aluminium phosphate or aluminium hydroxide). These prophylactics
today represent the principal means of controlling diphtheria. The toxoids
are standardised in Lf (Limes flocculans) according to Ramon’s (1923,1928)
flocculation method for in vitro titration. Lf is defined as that quantity of
toxin or toxoid that flocculates most rapidly when mixed with 1 AU
(antitoxic unit of the standard serum). It is common practice everywhere
to immunise infants with a combined vaccine containing either diphtheria
and tetanus toxoids, or diphtheria, tetanus toxoids and Bordetella pertussis
vaccine.
Routine methods of assay of toxinogeny in C. diphtheriae strains will be
treated in Section IX.
C. Schick test
1. General
Susceptibility to diphtheria may be checked by means of the Schick
test (1913), which determines the specific action of diphtheria toxin on the
skin. Intradermal injection of a small dose of toxin (1/50 MLD) in 0.2 ml
into the right forearm of non-immune individuals results in an erythematous
A. SARAGEA ET AL.
protection against all C. diphtheriae strains capable of causing toxaemic
diphtheria.
Toxin was obtained in-a crystalline form by Pope and Stevens in 1958.
The minimum lethal dose (MLD), which for the most active purified
preparations is less than 40 ng, was originally defined by Ehrlich as that
amount of toxin required to kill a 250g guinea pig on the fourth day,
following subcutaneous injection with three characteristic signs : gelatinous
and/or haemorrhagic oedema and local swelling at the site of inoculation,
adrenal congestion and haemorrhagic or clear exudate in the pleural and
peritoneal cavities. A few picograms injected into rabbit skin will produce
a visible reaction. As detailed above the toxin is very antigenic and is
neutralised by antitoxin.
Treatment with formalin converts toxin into an antigenic but non-toxic
product: toxoid (English), anatoxin (French). The specific intoxication
produced by the exotoxin in vivo can be specifically neutralised by antitoxin, and this reaction is important both for performing the Schick test in
man and as a rapid method of toxin-antitoxin titration in animals.
Large quantities of toxin are used for the preparation of toxoids as
prophylactics and as antigens, to obtain antitoxin in horses for passive
immunisation and for testing individual susceptibility to diphtheria by
means of the Schick test.
During the last decades highly immunogenic prophylactics have been
obtained by purification of diphtherial toxoid, and adsorption on aluminium
salts (aluminium phosphate or aluminium hydroxide). These prophylactics
today represent the principal means of controlling diphtheria. The toxoids
are standardised in Lf (Limes flocculans) according to Ramon’s (1923,1928)
flocculation method for in vitro titration. Lf is defined as that quantity of
toxin or toxoid that flocculates most rapidly when mixed with 1 AU
(antitoxic unit of the standard serum). It is common practice everywhere
to immunise infants with a combined vaccine containing either diphtheria
and tetanus toxoids, or diphtheria, tetanus toxoids and Bordetella pertussis
vaccine.
Routine methods of assay of toxinogeny in C. diphtheriae strains will be
treated in Section IX.
C. Schick test
1. General
Susceptibility to diphtheria may be checked by means of the Schick
test (1913), which determines the specific action of diphtheria toxin on the
skin. Intradermal injection of a small dose of toxin (1/50 MLD) in 0.2 ml
into the right forearm of non-immune individuals results in an erythematous