Summary
Remnant like lipoprotein particles (RLP) of partially catabolised human plasma chylomicrons
(CM) and very low density lipoproteins (VLDL) were separated from CM and VLDL using
two monoclonal antibodies, anti apo B-100 (JI-H) and anti apo A-I (H-12) coupled to
Sepharose 4B gel to form an immunoaffinity column. Lipoproteins containing apo B-100
or apo E, including VLDL and LDL adsorb to (JI-H)-gel, while CM and HDL with apo A-I
adsorb to (H-12)-gel. The unbound fraction (RLP) is rich in apo B-48, apo E and apo
E rich apo B-100 which has not been recognized by JI-H. The RLP fraction with a total
triglyceride of 12.35 ± 6.22 mg/ml; total cholesterol, 0.32 ± 0.08 mg/ml and total
protein, 0.72 ± 0.12 mg/ml (mean ± S.E.M, n = 9) was added to blood from healthy persons
at 2.5-200 |xl/ml and agitated gently at 37° C for 40 s. Platelet aggregation was
assessed by measuring the loss of single platelets. At 2.5-10 μl, RLP induced platelet
aggegation increased with the dose of RLP, but decreased at 25-200
julL
Scanning electron microscopy revealed that within 20 s of agitation in the presence
of RLP, activated platelets had appeared on the red cell membrane and within 40 s
of agitation, platelet aggregates had formed on the red cells. The platelet responses
were unaffected by aspirin (10 or 20 μg/ml) but were inhibited by cilostazol, a phosphodiesterase
type III inhibitor (0.4 to 1.6 μg/ml). It is likely that the platelet effect of RLP
is a consequence of RLP dependent red cell-platelet interaction. This is the first
report of platelet aggregation induced by RLP without an added platelet agonist.
