Aggregation of buffy-coat leucocytes. A simple, sensitive assay for cell-mediated immunity.

The addition of Tuberculin PPD to whole blood resulted in aggregation of the leucocytes. The degree of aggregation was assessed macroscopically and by two microscopic methods. The dose of PPD required to produce aggregation varied greatly between different subjects and an inverse correlation was noted between the dose of PPD needed and the Mantoux reaction.