However, murine fibrin clot is relatively resistant to lysis by murine plasminogen. Mouse and human fibrinogen are similar in formation of fibrin fibrils, crosslink modification by FXIIIa and interactions with platelet integrin α IIbβ 3 and leukocyte integrin α Mβ 2 in vivo. The mouse γ′ sequence is shorter than in human fibrinogen, but there are no data on its plasma levels nor its function. Approximately 15% of human fibrinogen consists of heterodimeric molecules with a γ′ chain which arises from alternative mRNA processing. The murine fibrinogen α-C domain contains three consecutive arginine-glycine-aspartic acid (RGD) sequences which are absent in human fibrinogen. Mouse fibrinogen chains are ∼70–90% identical to human chains (Homolo/Gene data bank of Entrez). It is a dimer with duplicate sets of Aα, Bβ and γ chains, products of three separate genes ( Fga, Fgb, Fgg Table 1) (the gene symbols used in this review are those recommended by the International Committee on Standardized Genetic Nomenclature for Mice, revised January 2006 accessed 20 February 2007). Fibrinogen Structure and functionįibrinogen is the substrate of thrombin in the coagulation cascade. Normal mouse PTs, which are also strain dependent, range from 9 to 12 s.
Laboratories should establish their own normal value for the PT, using the appropriate pooled mouse plasma or a defined human plasma. Therefore, human TF preparations are commonly used in mouse studies. The clotting time of the combination of crude mouse thromboplastin with mouse plasma is similar to that of human thromboplastin with mouse plasma. The prothrombin time (PT) assesses the TF pathway of coagulation by measurement of the time to coagulation of plasma, incubated with thromboplastin (TF plus phospholipids), followed by the addition of calcium. A normal mouse APTT value is 20–30 s, although higher values are also reported. It is advisable to prepare a pool of citrated control plasma, although a human reference standard may be substituted. Each laboratory should determine its own normal APTT value, using plasma from the mouse strain(s) studied, because the APTT is strain dependent (see also ). The main limitation is the small amount of plasma available. In the activated partial thromboplastin time (APTT), citrate-anticoagulated plasma is incubated with a contact activator, such as kaolin, in the presence of phospholipids without tissue factor (TF), calcium is added and the time to coagulation is recorded.ĪPTT kits for human plasma are adequate for the assay of mouse plasma. General screening tests give an overall assessment of the coagulation system and they form the basis of other coagulation assays.