Interaction of diphtheria toxin with cell cultures from susceptibile and resistant animals

Challenges of Diphtheria Toxin Detection

Diphtheria toxin (DT) is the main virulence factor of Corynebacterium diphtheriae, C. ulcerans and C. pseudotuberculosis. Moreover, new Corynebacterium species with the potential to produce diphtheria toxin have also been described. Therefore, the detection of the toxin is the most important test in the microbiological diagnosis of diphtheria and other corynebacteria infections. Since the first demonstration in 1888 that DT is a major virulence factor of C. diphtheriae, responsible for the systemic manifestation of the disease, various methods for DT detection have been developed, but the diagnostic usefulness of most of them has not been confirmed on a sufficiently large group of samples. Despite substantial progress in the science and diagnostics of infectious diseases, the Elek test is still the basic recommended diagnostic test for DT detection. The challenge here is the poor availability of an antitoxin and declining experience even in reference laboratories due to the low prevalence of diphtheria in developed countries. However, recent and very promising assays have been developed with the potential for use as rapid point-of-care testing (POCT), such as ICS and LFIA for toxin detection, LAMP for tox gene detection, and biosensors for both.

Observations on constitutional resistance to infection

The attention of most immunologists is held by the elaborate nonspecific and antigen-specific mechanisms of reactive immunity. There is, however, a more fundamental level of immunity to infection that is shared by all forms of life: constitutional resistance to infection. In this article, the nature and importance of constitutional immunity is illustrated using examples from population, cell and molecular biology.

Comparison of diphtheria intoxication in human and nonhuman cell lines and their resistant variants

Differences in sensitivity to diphtheria toxin of several toxin-sensitive and toxin-resistant human and non-human cell lines were compared. A method is described whereby it is possible to compare the sensitivity of one cell line with another and obtain meaningful quantitative results. Based on the concentration of toxin required to produce 50% inhibition of protein synthesis after 24 h of exposure the ID50 (24) value toxin-resistant cells were found to be 105 to 106 times more resistant to toxin than toxin-sensitive cells. There was little variation in the ID50 (24) values for cells in each of the two groups. The toxin-resistant cells used in this study, naturally resistant as well as selected variants, possess elongation factor 2 which is susceptible to inactivation by toxin. It is suggested that they are capable of activation of toxin but either cannot bind toxin or are unable to transport toxin across the plasma membrane. Protein synthesis is inhibited when these resistant cells are exposed to high concentrations of toxin. Under these conditions it is likely that enough toxin is able to bypass the block in toxin-specific entry and reach the cytosol by a second, less efficient, nonspecific mechanism to catalyze the inactivation of elongation factor 2 and inhibit protein synthesis.

Response of cultured mammalian cells to diphtheria toxin. IV. Isolation of KB cells resistant to diphtheria toxin

KB cell strains which are resistant to the lethal effects of diphtheria toxin were isolated from the toxin-sensitive KB cell line. For one such strain, KB-R2, the concentration of diphtheria toxin required to cause a 50% reduction of incorporation of amino acids into protein was more than 2,000 times that required in the sensitive KB-S cell. The KB-R2 strain was cloned by a single-cell isolation method to yield uniform strains with an even greater resistance to toxin. Resistance is a stable, inheritable property, providing a good genetic marker, and appears to be related to some alteration in the cell membrane. Preliminary studies showed that these cell strains are resistant to poliovirus and vesicular stomatitis virus as well as to toxin.

Diphtheria toxin subunit active in vitro

Exposure of diphtheria toxin to dithiothreitol (and similar thiols) resulted in a subunit which was active in catalyzing the adenosine diphosphateribosylation of mammalian aminoacyl-transferase II in the presence of nicotinamide adenine dinucleotide. At the same time there was a marked increase in total ADP-ribosylation activity. A molecule which was apparently identical to the derived subunit in size and activity was detected in partially purified preparations of toxin.

The response of cultured mammalian cells to diphtheria toxin. I. Amino acid transport, accumulation, and incorporation in normal and intoxicated sensitive cells

The response to diphtheria toxin of two sensitive cell lines, KB and HeLa, was investigated. Inhibition of the incorporation of radioactively labeled amino acids into protein was the earliest detectable effect of diphtheria toxin. It was observed that, during the period of intoxication, the cell membrane was morphologically intact and retained its semi-permeable character, although it was rendered fragile and more easily disrupted by mechanical manipulations than the normal cell. The transport of amino acids continued even after intoxicated cells had ceased to synthesize protein, and the levels accumulated were equal to those of control cells. It was observed that cultural conditions, age, and handling of cells affected their response to toxin. In early log phase cells subjected to a minimum of handling before application of the toxin, the normally observed latent period preceding detectable effects was reduced to 15 min for KB cells and 30 min for HeLa cells, shorter times than previously reported. The data are consistent with the hypothesis that diphtheria toxin enters susceptible cells, possibly by pinocytosis, and there acts upon cytoplasmic sites of protein synthesis.