In vitro determination of effects of dialyzable leukocyte extracts containing transfer factor activity.

The studies for determining the effects of dialyzable leukocyte extracts (transfer factor) as reflected in recovery of E-rosetting capacity in trypsinised lymphocytes (recovery-assay) suggested the following: 1. Dialyzable leukocyte extracts contain an inhibitor with a molecular weight of about 5000 (fraction I). 2. This inhibitor considerably affects the immunologic activity of both whole preparations and their different fractions during the in vitro activity assay. 3. The inhibitor fraction that fails to respond to the "recovery-assay" (less than 5%) responds very actively to the test after inactivation (45 min/57 degrees C). 4. Therefore, activation assays performed on the total preparation after inactivation involve a considerable error. 5. Immunological activity is concentrated in fractions III and IV. Only fraction III activity can be reduced considerably by inactivation. Fraction II activity is induced by incomplete separation from fraction III. Fraction IV cannot be inactivated. 6. In the case of transfer factor preparations (without inhibitor fractions) activity increases almost in direct proportion to the concentration up to about 30 micrograms. 7. Since the "recovery-assay" also responds to substances with no immunologic activity, its use can be justified in the case of fraction III. The activity is then the difference between the native and the inactivated forms. 8. A corresponding review of methods (such as LTT, migration inhibition test, skin test, etc.) currently used for activity assays seems advisable.