An immunohistochemical study of human platelets using a rabbit antibody against H18-K24 of apolipoprotein CIII (HATKTAK).

H18-K24 of human apolipopotein CIII (Apo CIII) (HATKTAK) is an activator of the macromolecular activators of phagocytosis from platelets (MAPPs). Using a rabbit antibody against HATKTAK, we performed an immunohistochemical study of human platelets. Indirect ELISA showed that this antibody reacts with Apo CIII-derived peptides with a C-terminal of HATKTAK, but not with Apo CIII. Immunoelectron microscopy revealed that reaction of anti-HATKTAK antibody occurred in the pseudopods of activated platelets. In blood coagula produced from the peripheral blood and formalin-fixed after various incubation periods, reaction of this antibody with platelets appeared rapidly with a peak at 3 to 6 h of incubation, and then diminished gradually. Leukocytes in the blood coagula were stained strongly positive. In tissue sections, fresh thrombi and hemorrhages with slight fibrin formation revealed a positive response of platelets to anti-HATKTAK antibody, whereas older ones with leukocytic infiltration, fibrin formation and organization did not. In addition to platelets, endothelial cells and leukocytes were stained positive by anti-HATKTAK antibody. All of the positive reactions by anti-HATKTAK antibody disappeared or diminished by co-incubation with HATKTAK. In conclusion, the anti-HATKTAK antibody reveals platelets during the early phase of activation.

Effects of D-allose on the endocytic activity of dendritic cells and the subsequent stimulation of T cells.

We examined the effects of a rare sugar, D-allose, which is 6-carbon monosaccharide, on endocytosis and T cell stimulation by dendritic cells (DCs). The endocytosis of BCG-anti-BCG immune complexes by DCs markedly decreased in D-allose-containing medium. Co-culture with T cells (mixed leukocyte reaction, MLR) of DCs, which had been exposed to BCG in D-allose-supplemented medium, induced apoptosis of CD4(+) T cells in a manner dependent on D-allose concentration. After the MLR, DCs cultured in the medium with D-allose expressed less CD40 and more Fas ligands than those cultured without D-allose. It was suggested that the functions of DCs, internalization, processing and the subsequent antigen presentation to T cells, are down-regulated via the action of d-allose.

Platelet high-density lipoprotein activates transferrin-derived phagocytosis activators, MAPPs, following thrombin digestion.

Macromolecular activators of phagocytosis from platelets (MAPPs), transferrin-derived phagocytosis activators released from platelets, activate leukocytic phagocytosis via Fcγ receptors. It has been found that MAPPs can be prepared using stored platelets or their lysate. Using this artificial MAPP production system, it has been found that they can be produced from precursors (tetrameric and dimeric transferrins) following reaction with a low-molecular-weight (LMW) activator of MAPPs, which is liberated from a high-molecular-weight activator of MAPP (HMW activator) by reaction with thrombin. In this study, the HMW activator in platelet lysate was characterized by assaying phagocytosis of washed neutrophils. In an ultracentrifugation study of the platelet lysate, HMW activator activity was observed in the fraction corresponding to the density of high-density lipoprotein (HDL). The activity was observed in the apolipoproteins obtained from the HDL fraction. Among the apolipoproteins tested only apolipoprotein CIII showed the activity to produce MAPP in vitro. Affinity chromatography of the apolipoproteins from the HDL fraction of the platelet lysate using an anti-apolipoprotein CIII column revealed that the substance that binds with the antibody showed MAPP-forming activity. In a gel filtration study of thrombin-treated apolipoprotein CIII, a peak of LMW activator activity was observed for fractions with a molecular size smaller than that of apolipoprotein CIII. Finally, MAPP-forming activity of HDL obtained from the plasma was examined. MAPP was formed only when delipidized HDL was used. In conclusion, it is suggested that platelet HDL is the HMW activator and that this activation is achieved via apolipoprotein CIII after thrombin reaction in platelets.