IMMUNOBIOLOGY OF DIPHTHERIA. RECENT APPROACHES FOR THE PREVENTION, DIAGNOSIS, AND TREATMENT OF DISEASE

Diphtheria outbreak in Jakarta and Tangerang, Indonesia: Epidemiological and clinical predictor factors for death

Background

In 2017, a diphtheria outbreak occurred in several provinces in Indonesia. The aim of this study was to identify predictors of mortality outcome of pediatric patients with clinical diphtheria.

Methods

A retrospective cohort study was conducted using patient medical records at five referral hospitals in the Province of Jakarta and one in Tangerang District, Banten Province during January 2017 to 31 August 2018. All children in the age group of 1–18 years old discharged with diagnosis of clinical diphtheria formed the study group. All anonymized patient data were evaluated for demographic issues, clinical features, immunization status, complication, laboratory profiles and outcome.

Results

A total of 283 patients with clinical diphtheria were included in the study group with case fatality rate of 3.5%. All mortal patients had the complication of myocarditis. Regression analyses revealed factors for predicting mortality. Incomplete primary diphtheria toxoid immunization, stridor, bull neck, leukocytosis ≥15 x10⁹ cells/L and thrombocytopenia ≤150 x10⁹ cells/L in each combination for 2 predictors modeling were correlated with death.

Conclusions

We report key predictors of mortality in pediatric patients with clinical diphtheria. The presence of these features when admitted to the hospital must be taken into account, because they can lead to fatal outcome.

EFFECT OF DIPHTHERIA TOXIN T-DOMAIN ON ENDOSOMAL pH

A key step in the mode of cytotoxic action of diphtheria toxin (DT) is the transfer of its catalytic domain (Cd) from endosomes into the cytosol. The main activity in this process is performed by the transport domain (Td), but the molecular mechanism of its action remains unknown. We have previously shown that Td can have some influence on the endosomal transport of DT The aim of this work was to study the effect of diphtheria toxin on the toxin compartmentalization in the intracellular transporting pathway and endosomal pH. We used recombinant fragments of DT which differed only by the presence of Td in their structure, fused with fluorescent proteins. It was shown that the toxin fragment with Td moved slower by the pathway early-late endosomes-lysosomes, and had a slightly different pattern of colocalization with endosomal markers than DT fragment without Td. In addition, endosomes containing DT fragments with Td had a constant pH of about 6.5 from the 10th to 50th minute of observation, for the same time endosomes containing DT fragments without Td demonstrated a decrease in pH from 6.3 to 5.5. These results indicate that Td inhibits acidification of endosomal medium. One of possible explanations for this may be the effect of the ion channel formed by the T-domain on the process of the endosomal acidification. This property of Td may not only inhibit maturation of endosomes but also inhibit activation of endosomal pH-dependent proteases, and this promotes successful transport of Cd into the cell cytosol.

Effect of the T-domain on intracellular transport of diphtheria toxin

Subunit B of diphtheria toxin (DT), which consists of two domains: R (receptor-binding) and T (transmembrane), plays an important role in toxin-receptor binding on the cell-targets and in transportation of catalytic subunit A to the cell cytosol. Recombinant analogues of the subunit B are promising representatives in the unique class of transporting proteins, able to deliver different types of biologically active molecules to cell cytosol. In the development of these protein constructs understanding of the role of each of the DT fragments in determination of transporting pathways of endocytosed complex toxin-receptor is urgently required. We have studied in this work the T-domain effect on intracellular transport of recombinant fragments of DT. We have compared intracellular transport of the R-domain and the subunit B, the last one consisted of both R-domain and T-domain. Recombinant fragments of DT used in this work were labeled with fluorescent proteins, which allowed applying colocalization technique for our study. Application of confocal microscopy technique revealed differences in transportation of recombinant derivates of DT in Vero cells: R-domain moved faster than subunit B to tubular compartments. Analysis of R-domain and subunit B transportation confirmed almost linear increase of their colocalization with the time regarding to Pearsons correlation coefficient (PCC). However, amount of colocalized with R-domain subunit B were not linearly increased with time according to Manders coefficient (M1), this could indicate the ability of subunit B to transport to such compartments that R-domain do not reach. Possible role of the T-domain in intracellular transportation and compartmentalization of the toxin may be associated with the ability of the T-domain to form a proton channels and its ability to interact with COPI complex.