Interferon-gamma-induced expression of class I HLA antigens on K-562 cells grown in serum-free medium

K-562 cells lack MHC class II expression due to an alternatively spliced CIITA transcript with a truncated coding region

The focus of this study was to determine the functional capacity of class II transactivator (CIITA), a regulatory factor of major histocompatibility complex (MHC) class II genes, in K-562 cells. We show that CIITA mRNA is present in K-562 cells and the interferon-gamma (IFN-gamma)-inducible CIITA promoter-IV exhibits low levels of basal activity, which is greatly enhanced upon treatment with IFN-gamma. Further study revealed that the CIITA cDNA contains an insertion of genomic sequence, which introduces a stop codon. The truncated coding region of the CIITA transcript in K-562 cells provides a possible explanation for the absence of MHC class II molecules.

Infection of a human leukemia K-562 cell line with Semliki Forest virus

Infection of the human leukemia hematopoietic stem cell line, K-562, with Semliki Forest virus (SFV) can be characterized by three stages: (1) an early virus-proliferating stage lasting 1 to 4 days post-infection (pi) in which infectious virus is produced in high titers (10(3)pfu/cell) but in which there is minimal cytopathic effect. All cells appear viable by trypan blue dye exclusion, although they do not proliferate, and DNA and cell protein synthesis decrease to less than 3% of uninfected controls within 24 hours; (2) an intermediate stage extending from day 5 to about day 24-30 pi in which the amount of infectious virus declines to low levels. During this stage, viral protein synthesis decreases to undetectable levels, although viral gylcoproteins are readily demonstrated by immunofluorescence and by immunoblot; however, capsid protein appears to degrade within 21 days pi. Cell numbers remain constant but the viability of the non-proliferating cells determined by trypan blue exclusion could not be determined with confidence; (3) a final long-term stage in which viral glycoproteins, E1 and E2, are detectable by immunoblots and immunofluorescence for many months but the cells are metabolically inactive and do not synthesize viral proteins. These non-viable cells do not lyse for as long as 2 years.