Joint cultivation of human erythroblastoid cells and mouse fibroblasts triggers release of a wide spectrum of cytotoxic factors.

It has been demonstrated that joint cultivation of human K-562 cells and mouse L-929 cells results in triggering apoptosis in L-929 cells and possibly also in K-562 cells. Analysis of proteins recovered from the culture medium has revealed the presence of three cytotoxic factors including TNF-alpha. This is the first observation of a release of cytotoxic factors by non-lymphoid cells in response to a direct contact with cells of different origin.

Functional architecture of chromosomal DNA domains.

More than 20 years ago, it was found that chromosomal DNA in eukaryotic cell nuclei was organized into large loops by periodic attachment to the high salt-insoluble proteinous nuclear (chromosomal) matrix. The specificity of genomic DNA partitioning into loops has been studied intensively trying to find out whether loops may constitute quasiindependent structural-functional units of the genome. These studies have resulted in conflicting findings and, consequently, in conflicting conclusions.

Large-scale fragmentation of mammalian DNA in the course of apoptosis proceeds via excision of chromosomal DNA loops and their oligomers.

It has been shown recently that apoptotic degradation of genomic DNA in mammalian cells starts by excision of large DNA fragments ranging in size from 50 kilobases to more than 300 kilobases. Although it was suggested that the above fragments could represent chromosomal DNA loops, the supposition was not supported by direct experimental evidence. In present work, we have studied the specificity of nucleolar and euchromatic gene long-range fragmentation in mouse and human cells triggered to undergo apoptosis either by tumor necrosis factor or by serum deprivation.

The specificity of human lymphocyte nucleolar DNA long-range fragmentation by endogenous topoisomerase II and exogenous Bal 31 nuclease depends on cell proliferation status.

The specificity of nucleolar DNA organization into loops in normal and activated to proliferation human lymphocytes has been studied using two different procedures of DNA loop excision. In the activated lymphocytes the nucleolar genes were found to be organized into loops of the same size as the size of individual rDNA repeat. The loops could be excised from the genome by DNA cleavage at matrix attachment sites with either the endogenous topoisomerase II or an exogenous nuclease Bal 31.

Heterogeneity of hepatitis B virus surface antigen in sera of patients with acute hepatitis B infection in relative content of the antigenic determinants a and preS2.

Using five ELISA variants we have analyzed the ratios of the antigenic determinants 'a' (a-D), preS2 (preS2-D) and the polymerized human serum albumin binding domains (PHSA-BD) in the hepatitis B virus surface antigen (HBsAg) particles contained in sera of three patients with acute viral hepatitis B. Quantitative relations between the a-D, preS2-D and PHSA-BD were shown to differ in these sera. Population of the HBsAg particles in each of the sera appeared heterogeneous in respect to the PHSA-BD activity.