Immunoprecipitation is a technique in which an antigen is isolated by binding to a specific antibody attached to a sedimentable matrix. It is also used to analyze protein fractions separated by other techniques such as gel filtration or density gradient sedimentation. The source of antigen for immunoprecipitation can be unlabeled cells or tissues, metabolically or intrinsically labeled cells, or in vitro-translated proteins. This unit describes a wide range of immunoprecipitation techniques, using either suspension or adherent cells lysed by various means. Usually, plasmas transfected cells or natural cells are ideal sample for immunoprecipitation.
K562 cell line is the first human immortalised myelogenous leukemia line to be established which is derived from a 53-year-old female CML patient in blast crisis. K562 cells are of the erythroleukemia type which are non-adherent and rounded, are positive for the bcr:abl fusion gene, and bear some proteomic resemblance to both undifferentiated granulocytes and erythrocytes.
In culture they exhibit much less clumping than many other suspension lines, probably due to the downregulation of surface adhesion molecules by bcr:abl. However, another study suggests that bcr:abl over-expression may virtually increase cell adherence to cell culture plastic. K562 cells can naturally develop characteristics similar to early-stage erythrocytes, granulocytes and monocytes and are easily killed by natural killer cells as they lack the MHC complex required to inhibit NK activity. They also lack any trace of Epstein-Barr virus and other herpesviruses. Over and above the Philadelphia chromosome they also exhibit a second reciprocal translocation between the long arm of chromosome 15 with chromosome 17.