Lymphocyte chalone from calf thymus: problems of large scale extraction and assay

Large scale extraction and assay of the lymphocyte chalone (LC), the natural lymphocyte proliferation inhibitor, require optimized, reproducible and standardizable methods. To this end we compared the effects on LC yield of storing thymus at different temperatures after collection from calves: Both quick freezing on solid CO2 and slow freezing at -50 degrees C led to a 30% loss of LC yield relative to that from unfrozen tissue kept at O degrees C. Moreover we found that the apparent decrease or total loss of LC activity upon storage of a purified LC fraction may result from an occasional lack of LC-responsiveness of human blood lymphocytes depending on the donor's physiological state, in spite of normal PHA reactivity. This suggested the use of LC-responsive, cryopreserved lymphocytes, the advantages of which are documented and discussed in detail.