- Paper Report
- Open Access
Release of autoantigens from apoptotic cells
- Carrock Sewell
© Current Science Ltd 1999
- Published: 18 November 1999
- systemic lupus erythematosus
Autoantibodies found in SLE sera are frequently directed towards antigens exposed during the "blebbing" phase of apoptosis. These blebs contain nucleosomes - DNA wound around a histone core, which have been cleaved by an endonuclease induced by caspases. To investigate the spectrum of autoantibodies to proteins induced by apoptosis in normal human serum and in sera from five patients with SLE.
Autoantibodies to 13, 21 and 33 kDa antigens were only seen in apoptotic lysates, and at much higher concentrations in SLE sera than in normal controls. These were identified as histone H4 (13 kDa band), H3, H2b and H2a (21 kDa), and H1a and H1b (33 kDa band). Blocking steps were used to confirm specificity. An immune complex precipitation step ensured that anti-DNA antibodies in DNA/histone complexes were not detected.
Apoptosis was induced in cell lines (Jurkat and U937) using a variety of techniques, and confirmed by both electron microscopy and annexin V/PI staining. Apoptosis-induced proteins were isolated by cell lysis in buffer solutions that preserved cytoplasmic but not nuclear antigens, ultracentrifuged and then electrophoresed. The proteins separated by electrophoresis were blotted onto nitrocellulose and probed with human sera.