Immunoglobulins from normal sera bind platelet vinculin and talin and their
proteolytic fragments
DM Reid, CE Jones, CY Luo and NR Shulman
Clinical Hematology Branch, NIDDK, NIH, Bethesda, MD 20892.
Our previous finding that normal serum immunoglobulins bind to internal
platelet proteins on Western blots led us to further identify these
proteins and determine the possible significance of autoantibodies against
them. A 95-Kd protein reactive with immunoglobulins in most normal sera and
easily confused with gpIIIa was shown to be a fragment of vinculin
generated by calpain proteolysis. Identity was established by peptide
sequencing of the protein purified from platelets stored without specific
protease inhibitors. Normal immunoglobulins bound intact vinculin (117 Kd)
and metavinculin (152 Kd), and their 105-, 95- , and 80- to 85-Kd
proteolytic fragments. IgG in 89%, and IgA and IgM in 100% of normal sera
reacted in titers of 10 to 1,000 with purified vinculin. In addition, IgG
in 79%, and IgA and IgM in 93% of normal sera reacted in titers of 10 to
5,000 with talin (235 Kd), another cytoskeletal protein, and its 200-Kd
proteolytic fragment. IgGs in sera from animals of several different
phylogenetic classes also reacted with human vinculin and talin on Western
blots. Frequency of occurrence, titers, and classes of antivinculin and
antitalin autoantibodies in patients with thrombocytopenia did not differ
discernibly from those of normal individuals. These antibodies had no
effect on platelet aggregation or clot retraction, and no apparent
pathogenic significance, but their widespread presence and the variability
in extent of proteolysis of platelet preparations used for Western blots
can complicate interpretation of patterns obtained with sera from patients
with presumed immune-mediated thrombocytopenias.
Volume 81,
Issue 3,
pp. 745-751,
02/01/1993
Copyright © 1993 by The American Society of Hematology
