Factor VIII Related Activities In Various Species

VIII coagulant antigen (VIII:CAg) and VIII related antigen (VIIIR:Ag) have been studied in various species using citrated plasma obtained from animals at the London Zoological Society Gardens.

VIII:CAg was measured by a one-site fluid phase immunoradiometric assay using an antibody to factor VIII arising in a patient with haemophilia. Fab' fragments were prepared and labelled with ¹²⁵I . A pool of 20 normal human plasmas was used as the standard. Three dilutions of each citrated animal plasma were tested in this assay. Bound antibody was separated from free by precipitation at 38% saturated ammonium sulphate (SAS).

VIIIR:Ag was measured by a similar one-site fluid phase immunoradiometric assay utilising a rabbit antihuman VI11R:Ag antibody (Behring). IgG purified from this antibody was labelled with ¹²⁵I and free antibody was separated at 25% SAS.

All the animals tested who had cross-reacting material present showed parallel dose response curves in the VIII:CAg assay - All species of monkeys had VIII:CAg levels within the normal human range (50-200 u/dl).Other mammals had detectable but lower levels - 8-47 u/dl with the exception of Guinea pig which had 111 u/dl. No detectable VIII:CAg was present in wild boar, red deer, goat, guanaco, onager or chicken plasma.

VIIIR:Ag activity was present in all animals tested except ferret and chicken, although in all cases the assay curves were non-parallel to the human standard plasma. The slopes of these curves were calculated and compared to the human plasma slope. As with VIII:CAg the closest values are seen in monkeys and apes.

Chicken plasma has no VIII:CAg or VIIIR:Ag and this or another avian plasma may be suitable for use as a carrier in immunoradiometric assays of human coagulation factors.