The biochemical structure of arterial microfibrils (MFS) is unknown. Presently, the
most probable hypothesis is that elastin associated MFS contain several antigenic
determinants with MW varying between 31 and 200 KD.
From our previous studies we know that MFS extracted by 6 M GuCl contain a major glycoprotein
with a 128 KD MV (GP128). GP 128 is essential for the reactivity of MFS towards blood
platelets but due tc the high insolubility of the extracted material it was not possible
to isolate and study this GP 128. We have used immunoblotting to determine if MFS
contain determinants recognized by antibodies against connective tissue glycoproteins
such as fibronectin, type VI collagen or anti-platelet thrombospondin (TSP). 'The
results showed that MFS do not contain fibronectin or type VI collagen but that anti-TSP
IgG reacted with GP 128. Furthermore, the Fab fragments from anti-TSP IgG inhibited
platelet aggregation induced by MFS but not by collagen or ADP . In a second step,to
raise antibodies against GP 128, we prepared blots from entire MFS, the nitrocellulose
band corresponding to GP 128 was cut, dissolved in DMSO, and wrs injected to rabbits.
Such obtained antibodies recognized only GP 128 in arterial MFS and also TSP in a
platelet lysate confirming that GP 128 and TSP have a common antigenic structure.
IgG from anti-GP 128 inhibit platelet aggregation induced by MFS but not by collagen
or ADP. Previously reported observations showed that tissue TSP and endothelial cells
derived GP 128 have a similar affinity for chromatography supports and have the same
effect on platelet-MFS interactions. All these results led us to propose that TSP,
GP 128, and MFS recognize a common determinant on platelet membrane. This assumption
would be strenghened if GP 128 indeed is derived from tissue TSP.
