platelet alpha-granules seem to be the source of this serum factor because 1 ) the activity is lacking in plasma , in serum prepared in the absence of platelets , and in serum prepared from a patient lacking platelet alpha-granules and 2 ) isolated mouse or human platelets release an immunostimulatory factor with very similar properties upon incubation with thrombin .
C0032105
plasma
C0229671
serum