Stretches of short, simple DNA sequences are widespread in all eukaryote genomes studied so far. Simple sequences are thought to undergo frequent expansion and deletion due to intrinsic genomic mechanisms. Some of the simple sequences were used successfully to detect hypervariable loci in various genomes. Hybridization experiments using synthetic probes not only revealed the informative simple repeats suitable for DNA fingerprinting in a particular species, but also reflected the wide range of distribution of the simple sequences among eukaryotes. The organization of these simple repetitive sequences at the chromosomal loci was investigated using in situ hybridization with chemically synthesized, pure oligonucleotide probes. Both biotin- and digoxigenin-attached probes detected specific chromosomal sites that are enriched in the respective simple-repeat blocks. Depending on the organism and probe used, accumulation of simple DNA sequences at individual or multiple sites on the chromosomes of different vertebrates could be demonstrated. The simple repetitive DNA sequences are located in different chromosomal regions (e.g., heterochromatin on the sex chromosomes, nucleolus organizer regions, and R-band sites), which are constrained considerably during evolution.

Amphibians↗

PubMedDate not supplied

delta Antigen in hepatitis B: immunohistology of frozen and paraffin-embedded liver biopsies and relation to HBV infection.

The finding that the recently described hepatitis B (HB)-associated delta antigen (delta Ag) is preserved in pronase-treated, formalin-fixed paraffin sections allowed a combined prospective and retrospective immunohistological study of its occurrence in 571 liver biopsies. Among 116 frozen biopsies (69 HBAg seropositive, 47 HBAg seronegative) and 455 paraffin-embedded biopsies (296 HBAg seropositive, 159 HBAg-negative), delta Ag was found in 10 HBAg seropositive patients. With the exception of 1 patient with chronic persistent HB, all had chronic-active HB and none had acute HB; 5 patients were i.v. drug abusers. In follow-up biopsies, the delta Ag persisted with HBsAg for as long as 6 years. The expression of delta Ag showed similarities to the HBcAg system including nuclear localization, mixed nuclear cytoplasmic expression, and coexistence with anti-delta in blood. The findings are compatible with the hypothesis that delta Ag represents a transmissible, defective viral agent which requires HBV as a helper and may modulate, but not terminate, ongoing HBV infection.

Antigen-Antibody Complex↗

PubMedDate not supplied

Prevalence and significance of anti-HBc IgM (radioimmunoassay) in acute and chronic hepatitis B and in blood donors.

Anti-HBc IgM was determined by a modified radioimmunoassay (RIA) in 35 patients with acute hepatitis B, 35 patients with chronic hepatitis B (7 with chronic persistent, and 28 with chronic active hepatitis), 157 HBsAg positive blood donors, and in 143 HBsAg negative but anti-HBc positive donors. The results of the RIA test were compared with those obtained by an ELISA technique. In chronic hepatitis, anti-HBc IgM was correlated with the occurrence of HBeAg, anti-HBe, Dane particles in the serum, HBsAg, and HBcAg in liver tissue and with biochemical and histological degrees of hepatic inflammatory activity. In acute self-limited hepatitis B, anti-HBc IgM (RIA and ELISA) was initially positive in all 35 patients. Twelve months after the acute illness, 94% of the patients were negative for anti-HBc IgM in the RIA test with only one patient showing a persistence of up to 18 months, whereas in the ELISA test anti-HBc IgM persisted in 17% of the patients over 2 years. In chronic hepatitis, the occurrence of anti-HBc IgM (RIA) showed a strong relation with the inflammatory activity, the anti-HBc IgM positive patients revealing a significantly more severe liver disease than did anti-HBc IgM negative patients. Anti-HBc IgM (RIA), however, did not correlate with the occurrence of HBeAg and Dane particles in the serum and HBcAg in liver tissue of patients with chronic hepatitis. Of the 157 HBsAg positive blood donors, anti-HBc IgM (RIA) could be demonstrated in 10 (6%), but in none of the 143 HBsAg negative, but anti-HBc positive donors, as compared to 43 (27%) and 9 (6%), respectively, in the ELISA test. Comparing the two test methods, the RIA exhibits higher specificity than did the ELISA due to a better blocking of nonspecific reactions, but possibly somewhat lower sensitivity. In this form, however, the RIA test is a more useful tool in the diagnosis of the different forms of hepatitis B virus infection and in determining the severity of chronic hepatitis B.

Blood Donors↗