[Immunological similarity of diphtheria toxin and EGF receptor].

Cardiomyopathy and neuropathy are the two commonly observed complications in diphtheria patients and in, some instances, individuals vaccinated against diphtheria. The nature of these complications remains not well understood. It was suggested that autoimmunity may play a role in the development of these afflictions. Based on functional similarities between diphtheria toxin (DT) and epidermal growth factor receptor (EGFR), which both can bind to the heparin-binding EGF-like growth factor (HB-EGF) precursors, we suggested that antibodies developed against DT can cross react with EGFR. Here, using serum from healthy donors (n = 10) and diphtheria patients (n = 15), we demonstrated that B-subunit of DT has the antigenic epitopes similar to those of EGFR. Diphtheria toxin as well as EGFR could be recognized by antibodies raised against EGFR and by serum antibodies from diphtheria patients. Moreover serum of diphtheria patients competitively inhibits binding of anti-EGFR antibodies to the receptor. The truncated diphtheria toxin without B-subunit could be detected by serum antibodies of diphtheria patients, but not by anti-EGFR antibodies. Collectively, these studies demonstrate cross-reactivity of antibodies raised against B-subunit of DT and extracellular domain of EGFR and suggest that clinically observed post-diphtheria complications may result from autoimmune inhibition of EGFR function and possible destruction of receptor-positive tissues.

[The intracellular degradation of 125I-EGF and the release of low-molecular degradation products under conditions of actin cytoskeleton disorganization]. / Vnutrikletochnaia degradatsiia 125I-EFR i vyvedenie nizkomolekuliarnykh produktov degradatsii v usloviiakh dezorganizatsii aktinovogo tsitoskeleta.

The influence of cytochalasin B (CB) on the epidermal growth factor (EGF) intracellular degradation and release of low-molecular products of degradation into the culture medium were investigated using two cell lines, A431 and 3T3. Investigated parameters were registered 3.0-4.5 h after the beginning of 125I-EGF endocytosis at 37 degrees C. With A431 cells it was shown that actin cytoskeleton disorganization significantly reduced the rate of 125I-EGF final degradation: a high amount of 125I-EGF, still retained cell-associated, and a reduced amount of low-molecular degradation products were released into the medium in experiments with CB addition. That is in agreement with our previous results (Barkan et al., 1988), revealing a long-term accumulation of EGF-rhodamine fluorescence in a juxtanuclear area of A431 cells after CB treatment. Nevertheless when similar experiments were performed on Swiss 3T3 cells, previously used as a model for demonstrating the inhibitory effect of CB on DNA synthesis stimulation by EGF (Barkan, Nikol'skii, 1986), we could not find such a distinct influence of CB on the process of degradation of internalised 125I-EGF.