Naturally occurring human IgG antibodies to intracellular and cytoskeletal components of human platelets

Abstract

SUMMARYImmunoblotting of platelets that have been subjected to SDS-PAGE has revealed thjit sera from normal individuals contain IgG which binds to many platelet components. This binding was seen with aulologous and heterologous platelets using serum of males and of nulliparous females who had not received blood transfusions. Although binding patterns of difTcrcnl sera were not identical, almost all sera caused IgG binding to platelet components of 87-90 kD, 140 kD (identified as vinculin) and 220-240 kD (tentatively identiiied as talin and actin-binding protein). Purified TgG showed the same binding pattern as whole seruni and F(ab')2 fragments retained iheir ability Lo bind lo many eomponents. The litre of IgG binding in serum was 1:50-1600 while thai of alloantibodies to the Pl'^' antigen was 1:3200. IgG bijiding components were not secreted when platelets were stimulated and were rarely associated wiih isolated membranes, bul were located either in platelet cyloplasm or cyloskcletons. IgG binding was decreased by absorbing sera with lysed platelets or isolated cytoskeletons. but only slightly with intact ptaleiels. Microaffinity purification oflgG which formed a major band on immunoblots showed that it was antibody with specificity for vinculin or its degradation products. These findings suggest that normiil sera contain naturally occurring IgG antibodies with specificity for intracellular platelet antigens ajid that in some cases their titre approaches thai of antibodies of pathological significance.

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