Investigation of Alternative Mechanisms of Collagen - Induced Platelet Activation by Using Monoclonal Antibodies to Glycoprotein IIb-IIIa and Fibrinogen

Anti-HuPl-ml (reactive with IIIa) and anti-C2G7 (reactive with the carboxyl terminal of the a chain of fibrinogen) were used to investigate platelet aggregation, fibrinogen binding and thromboxane synthesis induced by low dose collagen (LDC) or high dose collagen (HDC) in normal or aspirin treated platelets.

Anti-HuPl-ml and anti-C2G7 inhibited LDC induced platelet aggregation almost completely whilst abolishing fibrinogen binding; thromboxane production although reduced, still occurred. Thus LDC activation was dependent on fibrinogen binding to Gp IIIa. Aggregation of platelets induced by HDC was inhibited with anti-C2G7 or anti-HuPl-ml by 15-35% in association with a modest reduction in thromboxane (TxB2) production (with anti-HuPl-ml) and total inhibition of fibrinogen binding. When anti-HuPl-ml was added to aspirin treated platelets, aggregation with HDC although substantially reduced was not totally abolished.

Collagen appears to activate platelets in a dose related manner in which there are at least three possible mechanisms via: (i) GpIIb-IIIa and associated fibrinogen binding; (ii) prostaglandin pathway; (iii) an alternate pathway responsible for ∼20%-30% of platelet aggregation.

Use of the mannan receptor to selectively target vaccine antigens for processing and antigen presentation through the MHC class I and class II pathways

Extensive studies have shown that synthetic and recombinant vaccines developed against hemoparasites have not been as effective as whole parasites or crude membrane fractions in eliciting protective immunity. A possible reason is that synthetic vaccines are not being presented in a form that induces the appropriate immune response. We have developed a bovine model system to evaluate the ability of adjuvant compounds to induce an immune response to peptide antigens dominated by a cytokine profile with a Type 1 (cell-mediated) or Type 2 (humoral) bias. In the initial testing of this system, we found that mRNA expression of certain cytokines (interleukin [IL]-1beta, IL-6, IL-12, IL-15, GM-CSF, iNOS, and tumor necrosis factor [TNF]-alpha) is enhanced when monocyte-derived macrophages are stimulated with peptide antigen conjugated with mannan under oxidizing conditions compared to peptide conjugated with reduced mannan. The data suggest this model will be useful in identifying adjuvant systems that selectively modulate the cytokine profile of antigen presenting cells at the time of antigen presentation and the consequent downstream maturation of naive T cells to effector cells with Type 1 or Type 2 cytokine bias.