NATURAL HIDDEN ANTIBODIES REACTING WITH DNA OR CARDIOLIPIN BIND TO THYMOCYTES AND EVOKE THEIR DEATH

Both free and hidden natural antibodies to DNA or cardiolipin were obt ained from immunoglobulins of a normal donor, The free antibodies reac ting,vith DNA or cardiolipin were isolated by means of affinity chroma tography, Antibodies occurring in an hidden state were disengaged from the depleted immunoglobulins by ion-exchange chromatography and were then affinity-isolated on DNA or cardiolipin sorbents, We used flow cy tometry to study the ability of free and hidden antibodies to bind to rat thymocytes, Simultaneously, plasma membrane integrity was tested b y propidium iodide (PI) exclusion, The hidden antibodies reacted with 65.2 +/- 10.9% of the thymocytes and caused a fast plasma membrane dis ruption, Cells (28.7 +/- 7.1%) were stained with PI after incubation w ith the hidden antibodies for 1 h, The free antibodies bound to a very small fraction of the thymocytes and did not evoke death as compared to control without antibodies, The possible reason for the observed ef fects is difference in reactivity of the free and hidden antibodies to phospholipids, While free antibodies reacted preferentially with phos photidylcholine, hidden antibodies reacted with cardiolipin, and phosp hotidylserine. (C) 1997 Federation of European Biochemical Societies.